Probing Changes in the Local Structure of Active Bimetallic Mn/Ru Oxides during Oxygen Evolution
探究氧演化过程中活性双金属锰/钌氧化物局部结构的变化
- Michelle P. Browne* 米歇尔-布朗*Michelle P. Browne*Email: michelle.browne@helmholtz-berlin.deSchool of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin D02 PN40, IrelandHelmholtz Young Investigator Group Electrocatalysis: Synthesis to Devices, Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, GermanyMore by Michelle P. Browne
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- Carlota Domínguez 卡洛塔-多明格斯Carlota DomínguezSchool of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin D02 PN40, IrelandMore by Carlota Domínguez
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- Can Kaplan 卡普兰Can KaplanHelmholtz Young Investigator Group Electrocatalysis: Synthesis to Devices, Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, GermanyMore by Can Kaplan
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- Michael E. G. Lyons 迈克尔-里昂Michael E. G. LyonsSchool of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin D02 PN40, IrelandMore by Michael E. G. Lyons
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- Emiliano Fonda 埃米利亚诺-方达Emiliano FondaSAMBA Beamline, SOLEIL Synchrotron, L′Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette, FranceMore by Emiliano Fonda
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- Paula E. Colavita*Paula E. Colavita*Email: colavitp@tcd.ieSchool of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin D02 PN40, IrelandMore by Paula E. Colavita
Abstract 摘要
Identifying the active site of catalysts for the oxygen evolution reaction (OER) is critical for the design of electrode materials that will outperform the current, expensive state-of-the-art catalyst, RuO2. Previous work shows that mixed Mn/Ru oxides show comparable performances in the OER, while reducing reliance on this expensive and scarce Pt-group metal. Herein, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) are performed on mixed Mn/Ru oxide materials for the OER to understand structural and chemical changes at both metal sites during oxygen evolution. The results show that the Mn-content affects both the oxidation state and local coordination environment of Ru sites. Operando XAS experiments suggest that the presence of MnOx might be essential to achieve high activity likely by facilitating changes in the O-coordination sphere of Ru centers.
确定氧进化反应(OER)催化剂的活性位点,对于设计性能优于目前昂贵的最先进催化剂 RuO 2 的电极材料至关重要。.以前的研究表明,Mn/Ru 混合氧化物在氧进化反应中的性能相当,同时减少了对昂贵而稀缺的铂族金属的依赖。在此,我们对用于 OER 的混合 Mn/Ru 氧化物材料进行了 X 射线光电子能谱分析和 X 射线吸收光谱分析,以了解氧演化过程中两种金属位点的结构和化学变化。结果表明,锰含量会影响 Ru 位点的氧化态和局部配位环境。Operando XAS 实验表明,MnO x 的存在可能是实现高活性的关键,因为它可以促进 Ru 中心 O 配位层的变化。
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Attribution (BY): Credit must be given to the creator.
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You are free to share (copy and redistribute) this article in any medium or format and to adapt (remix, transform, and build upon) the material for any purpose, even commercially within the parameters below:
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电解水分裂是利用可再生资源生产清洁氢气的一种极具吸引力的工艺。氢气可作为能源载体储存起来,或在燃料电池中按需发电,这正是未来氢经济概念的基础。(1,2) 遗憾的是,电解水分裂仍处于研发阶段,因为目前使用的催化剂昂贵且稀缺,因此无法大规模生产出具有成本竞争力的绿色氢气。(3) 在整个电解水分离过程中,人们感兴趣的反应是发生在阴极的反应,即氢进化反应(HER),因为这是产生 H 2 的电极。(4,5)然而,水分离过程的瓶颈是发生在阳极的反应,即氧进化反应(OER),其产物为 O 2 。(6-10) 氧进化反应的最佳电催化剂是 IrO {{2} 和 RuO 2 。}这两种催化剂都属于铂族金属(PGM),价格昂贵且稀缺。(11,12)因此,要大规模利用水分离技术,就必须开发出与上述 PGM 具有类似活性,但成本更低且地球资源更丰富的新型电催化剂。(13)因此,开发和设计新型、可持续和活性材料作为 OER 催化剂是实现电解水分离的重要一步。
近年来,有关 Mn/Ru 基混合氧化物催化剂在 OER 中的高活性的报道层出不穷。(14-17) 例如,Pascuzzi 等人报告了在 RuO 2 -TiO 2 中添加不同数量的 Mn 对 OER 的影响。-TiO 2与纯 RuO 2 -TiO 2 相比对 OER 的影响。-TiO 2 对 OER 的影响。.在 Pascuzzi 等人的研究中,Mn 含量为 44% 的催化剂是最佳的 OER 催化剂,据报道,这是因为与纯 RuO 2 -TiO {{5} 相比,该催化剂的电化学表面更高。-TiO 2 面积更高,这是由于锰插入了 Ru 晶格。(14) 此外,Lin 等人通过第一原理计算发现,Ru/MnO 2 OER 催化剂的优异性能是由于锰在 Ru 晶格中的插入减少了催化剂的表面积。OER 催化剂的优异性能归功于能量势垒降低机制,该机制只涉及 *O 和 *OH 物种作为中间产物。(18)
此外,我们以前还报道过一系列基于 Mn/Ru 混合氧化物的高活性 OER 催化剂,这些氧化物是在 350 °C 退火温度下对前驱盐进行热分解而制成的。(15) 尽管氧化物催化剂基体中的 Ru 含量明显低于纯 RuO 2 ,但这些催化剂仍显示出卓越的 OER 活性。.原位 XRD 和 FTIR 测量显示,这些高性能材料中的锰中心具有混合 Mn 2+ /Mn 3+ 氧化反应。/Mn 3+ 氧化态,而 Ru 在合成材料中处于 +4 氧化态。然而,尽管这些变化对于了解这些锰/钌混合氧化物中的活性位点以及未来设计和优化替代性可持续混合氧化物电催化剂非常重要,但在 OER 期间或之后金属中心的氧化态和局部结构并未得到研究。
在过去十年中,原位和操作中 X 射线吸收光谱 (XAS) 已被成功用作一种工具,用于研究作为 OER 催化剂的各种金属氧化物(包括纯氧化锰和 Ru 氧化物)的活性位点。(19-24) XAS 特别有用,因为它对金属中心的局部结构非常敏感,包括嵌入无定形或无序相中的金属中心。例如,Jaramillo 及其合作者广泛采用 XAS 表征 MnO x 催化剂,以研究影响其 OER 活性的各种参数,如应用电位、孔隙率和支撑物的作用。(19,20,25) Lian 等人也用 XAS 表征了不同退火温度下多孔溶热制备的 MnO x 材料。 (21) 作者得出结论:退火温度在决定制备的 MnO x 催化剂的局部结构和锰氧化态方面起着重要作用,而这又与 OER 的活性趋势有关。此外,XAS 还被广泛用于确定纯 RuO {{3} 和基于 Fe、Ni、Co、Zn 和 Ir 的混合 RuO {{3} 异价取代材料的结构-活性关系。这些研究揭示了基于 RuO 2 的材料的活性位点是两个楔形基团。-(22,26,27) 与纯 RuO 2 相比,异价取代导致的 RuO 2 局部结构变化改变了混合材料的 OER 性能。.
值得注意的是,据我们所知,尽管混合锰/钌氧化物材料是制造低成本 OER 电催化剂的绝佳候选材料,但目前还没有对 OER 活性混合氧化物材料的局部结构进行原位/操作研究。在本研究中,我们旨在填补这一空白,并通过 XAS 实验对热制备的混合和纯 Mn/Ru 氧化物的局部化学和结构进行原位和运算表征,以确定氧化还原前后氧化物的变化。这将有助于对活性的起源有一个新的认识,并为新型混合氧化物低成本催化剂制定设计原则。
2. Experimental Methods 2.实验方法
2.1. Electrode Fabrication
2.1.电极制造
使用 Temescal FC-2000 电子束蒸发系统在清洁的硅晶片上沉积了 50 纳米金层上 150 纳米厚的钛层,制备了纯 Mn/Ru 混合氧化物电催化剂。之所以选择钛作为导电支持物,是因为在所研究的电位窗口内,钛不会显示出 OER 活性。(15) 通过溶解 (CH 3 COO) 2 Mn-4H 2 Mn-4H 2 Mn-4H 2 Mn-4H 2 Mn-4H 2Mn-4H 2O 和 RuCl 3 -xH 2 O 在丁醇中以不同比例混合;溶液分别在 10 mL 锥形烧瓶中配制,然后在热板上蒸发,直到溶剂残留量降至最低,从而形成用于配制工作电极的前体浆料。在钛/硅基底上涂上一层相关的金属浆料,覆盖面积为 1 cm 2 。然后在 90 °C 的烘箱中干燥 10 分钟,此过程重复一次。生成的电极在 350 °C 的温度下空气中退火 9 小时,以确保前驱体材料的分解。根据轮廓仪的估算,这样得到的钛支撑氧化膜电极厚度为 0.24 ± 0.6 μm。样品以 Mn/Ru 混合前驱体浆中 Mn 的摩尔含量百分比表示;例如,Mn 100 表示由 100% Mn 前驱体制备并在 350 °C 空气中处理的样品。
2.2. Characterization Methods
2.2.表征方法
报告中的 X 射线光电子能谱 (XPS) 测量是使用 VG Scientific ESCALab MKII 系统,利用 Al Kα X 射线源(1486.7 eV)进行的。调查扫描和高分辨率扫描的通过能量分别设置为 200 和 20 eV。结合能被校准为与硅/钛晶片支架上被动层相关的 TiO 2 峰值(458.5 eV)。(28) 在扣除雪莉背景并使用混合高斯-洛伦兹(30%)线形后,使用商业软件(CasaXPS)进行拟合。使用 Monte Carlo 误差分析对泊松调整光谱进行了面积不确定性估算。
在法国 SOLEIL 同步加速器的 SAMBA 光束线进行了 X 射线吸收近边结构 (XANES) 和扩展 X 射线吸收精细结构 (EXAFS) 测量。(29) MnO、Mn 3 的参考样品O 4 、α-锰 2 O 3 , β-MnO 2 , 和 RuO 2 。和 RuO 2 (Sigma)。(Sigma) 的石墨粉和 5 wt % 的相关 Mn 或 Ru 化合物制备成颗粒。参考样品以透射模式进行探测,而通过热分解制备的工作电极则以荧光模式在 45° 下进行探测,除非另有说明。在 Mn 和 Ru K 边收集光谱,并以 Mn(6540.0 eV)和 Ru(22117.0 eV)金属箔为基准进行能量校准。
氧化物电催化剂的原位 XAS 光谱最初是从制备好的样品的锰 K 边缘获得的。以 1 M NaOH 为电解液、铂丝为对电极、Hg/HgO 为参比电极的三电极电池中进行了原位外电化学实验。循环伏安法以 40 mV/s 的扫描速率进行。在 10 mA cm –2 的电流密度下进行了计时电位测定。.随后在锰 K 边再次对样品进行了原位表征。对于锰 K 边区的 EXAFS 分析,通过去除边缘上方的背景,并使用标准程序进行拟合,处理数据以获得振荡的 χ(k) 函数。简而言之,使用振幅为 dk = 1 的汉宁光栅化窗口,将 3 至 10.5 Ǻ 区域的电子伏特 (eV) 能量转换为 k 空间。然后对数据进行 k {{1}-对数据进行加权和傅里叶变换,以生成 Mn 周围的伪径向分布函数。
Ru K 边的原位和操作实验是使用定制的双电极池(图 S1)进行的,该池配备了铂对电极,可在 1 M NaOH 中进行 OER 活动时通过 Si/Ti 基底探测氧化物。数据分析使用 Athena 和 Artemis 软件包进行。根据 XANES 确定的边缘位置为归一化边缘吸光度一半时的能量。使用 FEFF v.8.4 和自洽电位计算散射路径。(31) EXAFS 数据按照 Newville 等人(29,30)的方法提取。傅立叶变换(FT)在 k = 3 和 11 Å –1 之间进行,使用振幅为 dk = 1 的汉宁光栅化窗口。EXAFS 信号按 k {{1} 加权,并按照 Newville 所描述的程序在 r 空间中进行拟合。(30)
3. Results and Discussion
3.结果与讨论
为了研究纯 Mn/Ru 氧化物材料和混合 Mn/Ru 氧化物材料在 OER 条件下的结构特性,本研究中的材料是在管式炉中以 350 °C 的温度对前驱盐材料进行热退火制备的。材料的制备方法与我们之前的论文类似;不过,由于本研究中原位/操作研究的性质,我们使用了平面硅/钛支架,而不是封装在玻璃中的金属丝。(15)
图 1a 显示了硅/钛衬底上的纯氧化锰/氧化钌和混合氧化锰/氧化钌材料在 1 M NaOH 溶液中的典型循环伏安图 (CV) 曲线。从 CV 曲线可以看出,Mn 100 材料是 OER 活性最低的材料,而在本研究测试的所有材料(Mn 100、Mn 90、Mn 50、Mn 10 和 Mn 0)中,Mn 50 材料的 OER 电流密度最高。此外,根据各自的电容贡献归一化后的 CV 曲线图(见图 S2)显示,相对于热制备的 RuO 2 材料,Mn 50 和 Mn 10 材料的活性相当或更高。.这表明,混合氧化物的 OER 电流密度的提高可能不仅仅是由于电化学比表面积的差异,而是由于内在活性的变化。
图 1b 还显示了在 OER 区域(电流密度为 10 mA cm –2 时)进行的计时电位测量,以评估纯 Mn/Ru 混合氧化物在更稳态条件下的 OER 活性,即与 CV 曲线相比,电容电流的影响较小;所有计时电位测量均按测量值显示,未进行欧姆降校正。对于计时电位测量,锰/钌材料的趋势与 CV 曲线的 OER 活动一致。应用欧姆滴校正后得到的曲线图也显示在 "辅助信息 "中,并表明混合氧化物的 OER 过电位都优于或与热制备的 RuO 2 的过电位相当,如图 15 所示。,(15) 如图 S3 所示。更值得注意的是,与 Mn 100 材料相比,所有 Mn/Ru 混合材料的 OER 催化剂性能都明显更好。
图 1 中的 OER 结果非常有趣,因为最先进的材料(RuO 2 )在稀释了 50%的廉价材料(氧化锰)后,显示出比 RuO 2 本身更好的 OER 活性。因此,用 Mn 50 而不是 RuO 2 催化 OER 可以降低与该反应相关的成本。此外,Mn/Ru 混合氧化物材料的结构设计也特别令人感兴趣,因为与最先进的催化剂相比,所获得的信息可用于合成更好、更便宜的 OER 催化剂。
为了了解纯 Mn/Ru 混合氧化物表面和主体金属中心的结构和氧化态,我们进行了 XPS 和 XAS 测量。图 2a 显示了在锰前驱体比例不断增加的情况下合成的材料的测量扫描图;在不含锰(锰 0)的情况下合成的材料的测量扫描图见佐证资料图 S4。所有扫描结果都显示了与电极基底产生的 Ti 2p(约 458 eV)(28,31)相关的峰值。约 285 eV 的 C 1s 峰来自残碳,而约 532 eV 的 O 1s 峰来自氧化物。532 eV 的 O 1s 峰来自氧化物的形成。含锰材料显示出 635-660 eV 范围内的 Mn 2p 双重峰 (32-35),而 Mn 0 和 Mn/Ru 混合氧化物则显示出 Ru 3d(约 282 eV)和 Ru 3p(约 464 eV)峰 (36),分别与 C 1s 和 Ti 2p 峰部分重叠。
图 2b 显示了锰/钌氧化物的锰 2p 双特的高分辨率光谱。光谱显示了混价锰氧化物特有的宽双特峰。(32,34) 所有氧化物的 2p 3/2 最大值的结合能都保持在 640.7-642.2 eV 的范围内。该值表明,锰 2p 光谱的主要贡献来自氧化态在 II-IV 范围内的锰中心。对 Mn 2p 双重谱进行了拟合,结果见图 2c-f;表 1 对拟合结果进行了总结。使用与 MnO 2 中 Mn(IV)相关的三个主要贡献(642.0-642.6)获得了最佳拟合结果。(642.0-642.6 eV)、锰 2 中的锰(III)O 3 (32) 图中所示的 2p 1/2 峰的拟合受到了限制,以满足相对于 2p 3/2 的 2:4 面积比和 11.5 eV 的能量分割。(33,35) 在 644.5-646 eV 处的第四个峰与 Mn(II)的卫星峰相对应,也需要对所有光谱进行满意的拟合,(32,33) 进一步证明材料中存在 Mn(II)中心。拟合结果表明,所有材料都显示出混合氧化态;然而,由于峰宽且能移相对较小,从 Mn 2p 拟合中明确确定平均氧化态具有挑战性(32)。
MnO2 氧化锰 {{0} | Mn2O3 锰 2 O 3 | MnO | satellite 卫星 | |||||
---|---|---|---|---|---|---|---|---|
eV | % area 面积百分比 | eV | % area 面积百分比 | eV | % area 面积百分比 | eV | % area 面积百分比 | |
Mn 100 锰 100 | 642.6 | 55 (1)% | 641.9 | 16 (2)% | 640.8 | 26 (2)% | 645.5 | 2.6 (1.0)% |
Mn 90 锰 90 | 642.6 | 53 (1)% | 641.9 | 28 (4)% | 640.8 | 16 (3)% | 644.6 | 3 (2)% |
Mn 50 锰 50 | 642.0 | 41 (1)% | 641.3 | 21 (1)% | 640.2 | 36 (1)% | 644.5 | 2.4 (0.4)% |
Mn 10 锰 10 | 642.0 | 37 (10)% | 641.3 | 19 (9)% | 640.2 | 40 (8)% | 645.6 | 4 (3)% |
Fit uncertainties are shown in parentheses.
a 括号内为拟合不确定度。
3.1. XAS Characterization at the Mn K-Edge
3.1.锰 K 边缘的 XAS 表征
XAS 用于研究 OER 活性前后锰中心周围的局部结构。图 3a 显示了制备的锰/钌混合氧化物材料在锰 K 边的归一化 XANES 光谱;图 3b 显示了参考氧化物 MnO、Mn 3 O 4 的 XANES 光谱。O 4Mn 2 O 3 O 3 和 MnO 2 的 XANES 边沿位置见表 S1。
图 3b 显示了根据已知参考氧化物氧化态的线性插值估算出的氧化态。(21,37) 混合锰/钌氧化物的边缘位置表明,锰的氧化态随着混合氧化物催化剂中锰含量的增加而降低。在大约在混合催化剂中,最初会出现 6552 和 6555 eV 处的可见肩;通常在氧化态较低的锰氧化物(如氧化锰)中会观察到这种肩 (20,37,38),这与图 2 中 Mn 2p 光谱中卫星的存在是一致的。
如图 2b 所示,Mn/Ru 混合氧化物的初始氧化态为 2.8 至 3.6,依次为 Mn 90、Mn 100、Mn 50 和 Mn 10。在纯锰催化剂(Mn 100)中观察到的锰价与在锰 2 和锰 3 中观察到的锰价 3.0 非常接近。O 3 和 Mn 3 O 4 中观察到的 3.0 的锰价非常接近。O 4表明 Mn 3+ 的贡献率高于 Mn 2+ 。.Mn 90 的 XANES 光谱与 Mn 3 O 4 的 XANES 光谱非常相似。O 4 参考。活性最高的 OER 催化剂(Mn 10 和 Mn 50)的边缘位置表明氧化态>3.0 但<4.0,它们的 XANES 光谱与 MnO 2 相似,表明可能会形成双氧化态。它们的 XANES 光谱显示与 MnO 2 相似,表明可能形成了桦烷石,MnO 3+ 中有 20-40% 的 Mn 3+ 中心,平均氧化态为 MnO 2 。19)有文献明确指出,氧化态高于 3.0 但低于 4.0 是锰基材料催化 OER 的最佳氧化态。(39)因此,在性能最佳的混合催化剂中观察到的锰氧化态与之前的研究结果一致。(39,40)
在电静电条件下,观察到 OER 后边缘位置明显上移(图 3c),同时约 6552 和 6555 eV 处的肩部贡献被普遍抑制。6552 和 6555 eV。这表明氧化还原反应后氧化物的局部结构发生了重大变化,低氧化态的锰中心比例下降。如图 3d 和表 2 所示,Mn 50 的平均氧化态变化尤其明显,与 Mn 10 几乎没有区别。值得注意的是,最佳 OER 材料 Mn 50 在 OER 之后的氧化态为 3.7,这是之前报告的性能最佳的锰氧化物的最佳范围。(39)
material 材料 | before OER 开放教育之前 | after OER 开放式教育之后 | Δ oxidation state (after–before) Δ 氧化状态(后-前) | ||
---|---|---|---|---|---|
edge position (eV) 边缘位置 (eV) | Mn oxidation state 锰的氧化态 | edge position (eV) 边缘位置 (eV) | Mn oxidation state 锰的氧化态 | ||
Mn 100 锰 100 | 6551.2 | 3.1 | 6551.7 | 3.2 | 0.1 |
Mn 90 锰 90 | 6549.9 | 2.8 | 6551.0 | 3.1 | 0.3 |
Mn 50 锰 50 | 6552.3 | 3.4 | 6554.0 | 3.7 | 0.3 |
Mn 10 锰 10 | 6553.8 | 3.6 | 6554.2 | 3.7 | 0.1 |
Mn 10-100 样品的 EXAFS 光谱(图 S7)进一步揭示了这些材料的结构以及在 OER 电位区进行电静电实验后局部结构的变化。图 4a 显示了傅立叶变换滤波 k 1 -weighted EXAFS 光谱。-加权的 EXAFS 图谱(|FT(k 1 χ(k)|),而图 4b 则显示了在钛涂层硅晶片上制备的 Mn/Ru 混合氧化物在实空间中的 |FT(k 1 χ(k)|的实际空间。Mn 100 在不同径向距离上显示出峰值,这些峰值可能与 MnO 2 和 Mn 3 的壳相对应。O 4 .上方 1.3 Å 处的散射最大值与 MnO 2 的主峰一致;然而,在 MnO 2 或 Mn 3 O 4 中可以发现 2.3 Å 和 3 Å 处的特征。O 4 参考文献中都可以找到 2.3 Å 和 3 Å 的特征,这些特征归因于第一个 Mn-O-Mn 配位层。(41,42)第一配位层的最佳拟合(图 S8,表 S2)得出的 Mn-O 间距为 1.89 Å,这表明存在 Mn 4+ 中心。(43)然而,第一层外壳的表观配位数也很低,远低于 6,这表明氧化态、位点占有(层、层间、边缘)和/或配体类型(-O、-OH、H 2 O)具有多重性,这与之前有关纳米晶植物锰酸盐的报道如出一辙。(42,44-46)因此,合适的结果与锰 100 的无序性和平均氧化态为 3.2 相一致,因为在这种材料中,锰 3+ 或可能的锰 2+ 位点的高比例会使锰-O 路径的 R 值达到或超过 2 Å。(42,43,46)
锰/钌混合氧化物的光谱在约 1.3 Å 处显示出与第一个 Mn-O 配位层相关的宽峰。1.3 Å 处的宽峰与第一个 Mn-O 配位层有关。(41) 在所有混合氧化物中出现的 2.3 Å 处的峰可归因于 MnO 2 或 Mn 3 O 4 。O4;然而,在 Mn 50 和 Mn 10 中突出显示的 3.1 Å 处的特征则清楚地表明了 Mn 3 O 4 的存在。O 4-型氧化物。最后,MnO 参考光谱中 2.7 Å 处最突出的峰归因于 Mn-O-Mn 配位层 (41),但在所有混合氧化物光谱中似乎都不存在。第一配位层的最佳拟合(图 S8,表 S2)表明,1.3 Å 处的峰值来自 Mn 4+ 中心特有的相对较短的 Mn-O 距离(1.85-1.89 Å)。值得注意的是,在锰 90 的情况中,配位数较低,与锰 100 一样接近 3,这与 XANES 的结果一致,即氧化态较低,因此较长 Mn-O 间距的比例较高。相反,锰 10 和锰 50 的配位数接近 4,为 1.89 Å,这与它们较高的估计氧化态一致。(43) 总之,氧化锰电催化剂显示出与混合氧化态一致的无序结构;与纯锰 100 材料相比,最活跃的锰 50 和锰 10 材料显示出无序的局部结构和混合价,其中锰 4+ 中心的贡献更大。
利用 EXAFS 分析研究了 OER 活性对氧化物中锰环境的影响,结果如图 5 所示;表 S3 和图 S8 中报告了 EXAFS 光谱和第一配位层的最佳拟合。图 5a-d 显示了|FT(k 1 χ(k)|在实际空间中的对比,分别是锰 100、锰 90、锰 50 和锰 10 样品在 OER 电致静电实验前后的对比。结果表明,所有混合氧化物都发生了重大变化,尤其是与第一配位层相对应的峰值。就锰 90 而言,|FT(k 1 χ(k 1 |shχ(k)| 的第一个峰的平均位置移动了约 0.2 Å。Mn 50 的 |FT(k 1 χ(k)|振幅大幅增加(图 5c),因此 OER 后的配位层与 MnO 2 参考材料的配位层非常相似(图 4b)。最短 Mn-O 距离的配位数的变化也说明了这一点(表 S2 和 S3),该配位数增加到接近 6 的值,而其 R 值保持不变,这表明在 OER 之后,Mn 50 的 Mn 4+ 中心比例增加。这与图 3d 中观察到的估计平均氧化态的增加是一致的,并支持这样的结论,即 OER 活动会导致混合氧化物材料中 Mn 的局部结构发生变化,特别是平均氧化态的增加。
3.2. XAS Characterization at the Ru K-Edge
3.2.Ru K 边缘的 XAS 表征
对热制备的纯氧化钌(Mn 0)、锰/氧化钌混合材料和 RuO 2 参考材料的 Ru K 边沿进行了进一步的 XAS 测量,以深入了解这些材料的 OER 活性。图 6a 显示了 Mn 0-90 在开路电位 (OCP) 下浸入 NaOH 电解质溶液时获得的 XANES 图谱;图中还显示了市售 RuO 2 的 XANES 图谱,以供比较。由于 Ru 核心空穴的宽度相对较大,因此 Ru 边缘位置出现了约 1.5 eV 的偏差(表 S4)。(47) 边缘位置约为 22129 eV:低于塔拉斯康研究所测定的 Ru 5+ 和 Ru 6+ 分别约为 22 132 和 22 134 eV 的值。和 Ru 6+ 的边缘位置分别低于 Tarascon 和合作者测定的约 22,132 和 22,134 eV 的值 (48),并且接近我们为 RuO 2 参考测量的边缘位置,因此表明所有混合氧化物的氧化态可能都是 +4。
为了了解 OER 过程中的氧化态,通过施加 1、10 和 20 mA cm {{0} 的电流对 Mn 0 催化剂进行了操作性 XANES 测量(图 6b)。(图 6b)。在 OER 区域,随着电流的增加,边缘位置没有发生明显的移动,光谱曲线也没有发生变化。同样,如图 6c、d 所示,在 10 mA cm {{1} 电流输出下的 OER 活动中,也没有检测到 Mn 10 或 Mn 50 的边缘位置发生变化。这些结果表明,在 OER 期间,Mn 0 或混合氧化物中的大多数探针 Ru 中心的氧化态没有发生重大变化。
对 Ru K 边进行了原位 EXAFS 分析,以进一步检查纯氧化物和混合 Mn/Ru 氧化物的局部结构是否发生了变化,这些变化可能与 OER 性能有关(图 S9)。通过与参考 RuO 2 进行比较,研究了 Mn 0 (Ru 100) 样品的结构(图 7)。(图 7);与金红石一样,Mn 0 催化剂的局部结构似乎涉及 RuO 6 在第一层外壳中的配位,但与结晶 RuO 2 的结构不同,这是因为与 Ru-Ru 距离相关的较长 R 值(约 3.2 Å)处的峰存在偏差。八面体配位也得到了第一壳拟合的支持(图 S10,表 S5),拟合得到的平均 Ru-O 1 间距为 1.96 Å,与文献数据十分吻合。(49) 当施加 10 mA cm {{4} 和 20 mA cm {{4} 的 OER 电流时,可以观察到 Ru-O 1 间距的有限变化。(49) 在施加 10 mA cm {{4} 和 20 mA cm {{4} 的 OER 电流时,可以观察到第一配位层的傅立叶变换发生了有限的变化;最佳拟合结果表明,Ru 中心与配体的平均 RuO 6 配位距离约为 1.96 Å。在 O 2 演化过程中,Ru 中心与配体的平均配位保持在约 1.96 Å。Ru-Ru 的贡献接近于参考 RuO 2 材料的位置和高度。
将 Mn 0 的 EXAFS Ru 边缘曲线与 Mn 10 和 Mn 50 混合锰/钌氧化物的 Ru 边缘曲线进行了比较;图 8a 显示了浸泡在 1.0 M NaOH 中的样品的比较结果。锰 10 的结构显示了锰 0 样品中 RuO 2 结构的主要特征,第一配位层与 Ru-O 相对应,3.2-3.6 Å 处的贡献来自 Ru-Ru 间距。在 Mn 50 的情况下,主要配位层仍然可以从光谱中看出,但相对于 Mn 0 结构,其有序度的变化非常明显。第一配位层的拟合结果表明,锰 10 和锰 50 都保持了八面体配位;然而,与锰 0 样品相比,这些混合氧化物中的平均 Ru-O 距离略大(图 S10,表 S5),这可能是由于局部无序造成的。这部分是由于在我们之前的工作(15)中通过 XRD 在 Mn 50 样品中检测到了金属 Ru (50),这与 XANES 光谱的线性组合拟合分析一致(图 S11 和表 S6)。锰 90 样品的 EXAFS 信号较弱(数据未显示),这是因为该样品的 Ru 含量最低,因此无法对其结构进行详细分析。
在 10 mA cm {{0} 电流下的 OER 期间记录了混合锰/钌催化剂的 EXAFS 光谱(图 8),锰 50 在 20 mA cm {{1} 电流下也记录了 EXAFS 光谱(图 S9)。(图 8)和 20 mA cm {{1} 下 Mn 50 的 EXAFS 光谱(图 S9)。就锰 10 而言(图 8b),其变化与锰 0 样品观察到的变化相当,即在 OER 期间,1.9、3.2 和 3.6 Å 处的峰的径向距离没有发生变化,而峰强度的变化则表明第一 O 配位层和 Ru-Ru 壳发生了有限的重组。对于高活性的 Mn 50 样品(图 8c),与在 NaOH 中的样品相比,在 O 2 演化过程中的 EXAFS 信号有明显的不同,这表明 Ru 中心周围发生了显著的结构重排。在 10 mA cm {{3} 的 OER 期间,Ru 金属峰非常明显。}根据 RuO {{4} 和 Ru 金属箔参考的线性组合拟合(图 S11 和表 S5),可以计算出在 OER 期间 Mn 50 样品中仍然存在金属 Ru。值得注意的是,局部结构的最大变化出现在 Mn 50 样品中,即 Mn 含量最大、可成功进行操作表征的样品。这可能是由于大部分 Ru 边沿信号来自高活性 Ru 中心,对于这些 Ru 中心,局部重排变得更加明显,较少被金红石型 RuO 2 相(如 Mn 0)的存在所掩盖。值得注意的是,第一层外壳的最佳拟合结果表明,平均 Ru-O 配位数增加,这在电流密度增加时变得更加明显(图 S10,表 S5)。尽管与第一邻域数相关的不确定性很大,但总体趋势表明,高活性的 Mn/Ru 50:50 氧化物具有显著的配位灵活性,并且在氧演化过程中形成了高配位的 Ru 物种。鉴于第一 Ru-O 间距的变化有限,这可能涉及氧化态的增加。
N>6的自适应配体球被认为是设计高翻转均相氧化还原催化剂的关键;(51)因此,我们的观察结果表明,在这些混合氧化物电催化剂的反应条件下,O配体球也会发生扩展,这一点很耐人寻味。正如之前有机金属文献中强调的那样,配体球的扩展可能伴随着大于 +4 的氧化态的稳定;(51)然而,鉴于在 Ru 边 XANES 中观察到的变化有限,很难确认这是否确实发生在 Mn 50 的 OER 过程中。
与之前的文献研究一致,本研究中的 CV 和时变测量结果表明,Mn/Ru 混合氧化物显示出巨大的潜力,可以取代较昂贵的 RuO {{0} 催化剂用于 OER。特别是价格较低的 Mn 50 和 Mn 10 显示出良好的 OER 活性,与纯 RuO 2 催化剂相比具有竞争力。
为了了解这些氧化物的性能优于纯 RuO 2 催化剂的原因,我们采用了原位和原位 XAS 方法来确定混合氧化物中两种金属中心的氧化态和配位壳与金属成分的函数关系。对 Mn K-edge 的 XANES 分析表明,随着 Mn/Ru 混合氧化物中 Mn 含量的增加,制备材料中 Mn 的平均氧化态降低,即 Mn 10 的氧化态最高,而 Ru K-edge 位置表明存在氧化态为 +4 的 Ru 中心。从 EXAFS 测量结果来看,第一个 Mn-O 配体球表明在所有混合氧化物中都存在 Mn 4+ 中心,但其比例随着 Ru 含量的降低而降低。重要的是,在 Mn 50 中观察到了高度的结构紊乱;事实上,在 OER 之后,这种氧化物中的 Mn 局部结构发生了显著变化,这表明相对于原始样品,Mn 4+ 中心的浓度有所增加。
还在操作条件下对 Ru 中心进行了研究,以监测氧演化过程中局部结构的变化。对 Ru 边缘进行的操作性 EXAFS 分析表明,在高电流的氧演化过程中,Mn 50 的局部结构尤其会发生变化。最佳拟合结果表明,通过配体球的扩展,第一配位层发生了扰动。我们推测这可能会使 Ru 稳定在较高的氧化态;然而,XANES 图谱并没有显示出可能与之相伴的显著变化。
根据我们的研究结果,我们可以推测 MnO x 相在二元或 Mn/Ru 混合氧化物中赋予高 OER 活性的作用。根据 EXAFS/XANES 结果,在 OER 过程中,Ru 和 Mn 中心的结构似乎发生了重大变化。MnO x 相的作用可能有两个方面:首先,我们注意到与 RuO x 的混合会影响 Mn 中心的平均氧化态,因此这种调谐效应可能是 Mn 10 或 Mn 50 等材料活性增强的部分原因。其次,混合氧化物中 Ru 中心周围的局部结构似乎是高度无序的,对于性能最好的混合氧化物来说,在氧演化过程中会发生变化,MnO x 的含量可能会使活性 Ru 位点周围的配位更加灵活。
这项研究为如何调整混合氧化物电催化剂中的 MnO x 含量以实现 OER 提供了重要见解。特别是,与纯 RuO 2 相比,Mn 50 和 Mn 10 材料的成本更低,OER 性能更好,因此这些催化剂在水分离应用中具有吸引力和成本竞争力。
Data Availability 数据可用性
The data related to the findings of this work are available from the corresponding authors, subject to reasonable request.
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Supporting Information 辅助信息
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Additional chronoamperometry, cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction, EXAFS spectra, best fits and parameters for the first coordination shell, and fit results of the XANES spectrum of Mn 50 (PDF)
附加的计时器、循环伏安法、X 射线光电子能谱、X 射线衍射、EXAFS 光谱、第一配位层的最佳拟合和参数,以及 Mn 50 的 XANES 光谱的拟合结果 ( PDF)
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M.P.B. would like to acknowledge the Helmholtz Association’s Initiative and Networking Fund (Helmholtz Young Investigator Group VH-NG-1719). This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 748968 (EDGE-FREEMAB). The results of this publication reflect only the authors’ view and the Commission is not responsible for any use that may be made of the information it contains. This publication has also emanated from research conducted with the financial support of Science Foundation Ireland under Grants No. 13/CDA/2213 and SFI/10/IN.1/I2969. The authors acknowledge SOLEIL for provision of synchrotron radiation facilities through Grant No. 20150740. The authors are grateful to Dr. H. Nolan for assistance with thickness determinations. For the purpose of Open Access, the authors have applied a CC BY public copyright license to any Author Accepted Manuscript version arising from this submission.
This article references 51 other publications.
- 1Zeng, K.; Zhang, D. Recent progress in alkaline water electrolysis for hydrogen production and applications. Prog. Energy Combust. Sci. 2010, 36, 307– 326, DOI: 10.1016/j.pecs.2009.11.002Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXis1OqtLw%253D&md5=fb3b70cabefcb81fd4fc2ab3a228a3fbRecent progress in alkaline water electrolysis for hydrogen production and applicationsZeng, Kai; Zhang, DongkeProgress in Energy and Combustion Science (2010), 36 (3), 307-326CODEN: PECSDO; ISSN:0360-1285. (Elsevier Ltd.)A review. Alk. water electrolysis is one of the easiest methods for hydrogen prodn., offering the advantage of simplicity. The challenges for widespread use of water electrolysis are to reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. This literature review examines the current state of knowledge and technol. of hydrogen prodn. by water electrolysis and identifies areas where R&D effort is needed in order to improve this technol. Following an overview of the fundamentals of alk. water electrolysis, an elec. circuit analogy of resistances in the electrolysis system is introduced. The resistances are classified into three categories, namely the elec. resistances, the reaction resistances and the transport resistances. This is followed by a thorough anal. of each of the resistances, by means of thermodn. and kinetics, to provide a scientific guidance to minimising the resistance in order to achieve a greater efficiency of alk. water electrolysis. The thermodn. anal. defines various electrolysis efficiencies based on theor. energy input and cell voltage, resp. These efficiencies are then employed to compare different electrolysis cell designs and to identify the means to overcome the key resistances for efficiency improvement. The kinetic anal. reveals the dependence of reaction resistances on the alk. concn., ion transfer, and reaction sites on the electrode surface, the latter is detd. by the electrode materials. A quant. relationship between the cell voltage components and c.d. is established, which links all the resistances and manifests the importance of reaction resistances and bubble resistances. The important effect of gas bubbles formed on the electrode surface and the need to minimise the ion transport resistance are highlighted. The historical development and continuous improvement in the alk. water electrolysis technol. are examd. and different water electrolysis technologies are systematically compared using a set of the practical parameters derived from the thermodn. and kinetic analyses. In addn. to the efficiency improvements, the needs for redn. in equipment and maintenance costs, and improvement in reliability and durability are also established. The future research needs are also discussed from the aspects of electrode materials, electrolyte additives and bubble management, serving as a comprehensive guide for continuous development of the water electrolysis technol.
- 2Rao, R. R.; Kolb, M. J.; Halck, N. B.; Pedersen, A. F.; Mehta, A.; You, H.; Stoerzinger, K. A.; Feng, Z.; Hansen, H. A.; Zhou, H.; Giordano, L.; Rossmeisl, J.; Vegge, T.; Chorkendorff, I.; Stephens, I. E. L.; Shao-Horn, Y. Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution. Energy Environ. Sci. 2017, 10, 2626– 2637, DOI: 10.1039/C7EE02307CGoogle Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVegt7bP&md5=61b7de504c9911da215e21cb94bb9505Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolutionRao, Reshma R.; Kolb, Manuel J.; Halck, Niels Bendtsen; Pedersen, Anders Filsoee; Mehta, Apurva; You, Hoydoo; Stoerzinger, Kelsey A.; Feng, Zhenxing; Hansen, Heine A.; Zhou, Hua; Giordano, Livia; Rossmeisl, Jan; Vegge, Tejs; Chorkendorff, Ib; Stephens, Ifan E. L.; Shao-Horn, YangEnergy & Environmental Science (2017), 10 (12), 2626-2637CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)While the surface at. structure of RuO2 has been well studied in ultra high vacuum, much less is known about the interaction between water and RuO2 in aq. soln. In this work, in situ surface X-ray scattering measurements combined with d. functional theory (DFT) were used to det. the surface structural changes on single-crystal RuO2(110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogen electrode (RHE) could be attributed to surface transitions assocd. with the successive deprotonation of -H2O on the coordinatively unsatd. Ru sites (CUS) and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant to the oxygen evolution reaction (OER), an -OO species on the Ru CUS sites was detected, which was stabilized by a neighboring -OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with their energetics from DFT led to a new OER pathway, where the deprotonation of the -OH group used to stabilize -OO was found to be rate-limiting.
- 3Demirbas, A. Future hydrogen economy and policy. Energy Sources, Part B 2017, 12, 172– 181, DOI: 10.1080/15567249.2014.950394Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjs1Gis70%253D&md5=e90e9a2c5704207ac49bfe52e504b75cFuture hydrogen economy and policyDemirbas, AyhanEnergy Sources, Part B: Economics, Planning and Policy (2017), 12 (2), 172-181CODEN: ESPBAC; ISSN:1556-7249. (Taylor & Francis, Inc.)A review. Hydrogen is not a primary fuel. It must be produced from water with either fossil or renewable energy sources. Thermochem. conversion processes, such as pyrolysis, gasification, and steam gasification, are available for converting the biomass to a more useful energy. Hydrogen can be generated from carbon-neutral biomasses or carbon-free energy sources such as elec., solar, and wind energy. In this way, the use of hydrogen could eventually eliminate harmful gas emissions from the energy sector. Vehicles and stationary power generation fuelled by hydrogen are zero-emission devices at the point of use, with consequential local air-quality benefits. Hydrogen is clean and a high-energy content of fuel. Hydrogen is a peaceful energy carrier for all countries. Raw material resources of fossil fuels geog. did not distribute homogenously in the world. However, the most important source of hydrogen is water, which is almost not dependent on geog. This advantage in the development of the hydrogen economy is the most important driving force. The hydrogen economy is a vision for a future in which hydrogen replaces fossil fuels. A major dilemma now faced by the developing countries is how to invest in hydrogen research and development for the transition to hydrogen economy. The increase in the consumer sectors that energy provides is necessary for both economic and social development in the developing countries. Policy-makers will need to pay more attention to the implications for the transition to hydrogen economy.
- 4Benck, J. D.; Hellstern, T. R.; Kibsgaard, J.; Chakthranont, P.; Jaramillo, T. F. Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide Nanomaterials. ACS Catal. 2014, 4, 3957– 3971, DOI: 10.1021/cs500923cGoogle Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslahsLzJ&md5=369e7a83d320ba0b9be9f79a8db74875Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide NanomaterialsBenck, Jesse D.; Hellstern, Thomas R.; Kibsgaard, Jakob; Chakthranont, Pongkarn; Jaramillo, Thomas F.ACS Catalysis (2014), 4 (11), 3957-3971CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review. We discuss recent developments in nanostructured molybdenum sulfide catalysts for the electrochem. hydrogen evolution reaction. To develop a framework for performing consistent and meaningful comparisons between catalysts, we review std. exptl. methodologies for measuring catalyst performance and define two metrics used in this perspective for comparing catalyst activity: the turnover frequency, an intrinsic activity metric, and the total electrode activity, a device-oriented activity metric. We discuss general strategies for synthesizing catalysts with improved activity, namely, increasing the no. of elec. accessible active sites or increasing the turnover frequency of each site. Then we consider a no. of state-of-the-art molybdenum sulfide catalysts, including cryst. MoS2, amorphous MoSx, and mol. cluster materials, to highlight these strategies in practice. Comparing these catalysts reveals that most of the molybdenum sulfide catalysts have similar active site turnover frequencies, so the total electrode activity is primarily detd. by the no. of accessible active sites per geometric electrode area. Emerging strategies to overcome current catalyst limitations and potential applications for molybdenum sulfide catalysts including photoelectrochem. water splitting devices and electrolyzers are also considered.
- 5Shi, X.; Fields, M.; Park, J.; McEnaney, J. M.; Yan, H.; Zhang, Y.; Tsai, C.; Jaramillo, T. F.; Sinclair, R.; Nørskov, J. K.; Zheng, X. Rapid flame doping of Co to WS2 for efficient hydrogen evolution. Energy Environ. Sci. 2018, 11, 2270– 2277, DOI: 10.1039/C8EE01111GGoogle Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVKqsLvJ&md5=4ba0f849e4ea85776316aae4f24c78ddRapid flame doping of Co to WS2 for efficient hydrogen evolutionShi, Xinjian; Fields, Meredith; Park, Joonsuk; McEnaney, Joshua M.; Yan, Hongping; Zhang, Yirui; Tsai, Charlie; Jaramillo, Thomas F.; Sinclair, Robert; Noerskov, Jens K.; Zheng, XiaolinEnergy & Environmental Science (2018), 11 (8), 2270-2277CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Transition metal sulfides have been widely studied as electrocatalysts for the hydrogen evolution reaction (HER). Though elemental doping is an effective way to enhance sulfide activity for the HER, most studies have only focused on the effect of doping sulfide edge sites. Few studies have investigated the effect of doping the basal plane or the effect of doping concn. on basal plane activity. Probing the dopant concn. dependence of HER activity is challenging due to exptl. difficulties in controlling dopant incorporation. Here, we overcome this challenge by first synthesizing doped transition metal oxides and then sulfurizing the oxides to sulfides, yielding core/shell Co-doped WS2/W18O49 nanotubes with a tunable amt. of Co. Our combined d. functional theory (DFT) calcns. and expts. demonstrate that the HER activity of basal plane WS2 changes non-monotonically with the concn. of Co due to local changes in the binding energy of H and the formation energy of S-vacancies. At an optimal Co doping concn., the overpotential to reach -10 mA cm-2 is reduced by 210 mV, and the Tafel slope is reduced from 122 to 49 mV per decade (mV dec-1) compared to undoped WS2 nanotubes.
- 6Lyons, M. E. G.; Doyle, R. L.; Browne, M. P.; Godwin, I. J.; Rovetta, A. A. S. Recent developments in electrochemical water oxidation. Curr. Opin. Electrochem. 2017, 1, 40– 45, DOI: 10.1016/j.coelec.2016.12.005Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVGgsL%252FO&md5=81acaad77943c99dd7e37ca020914cbeRecent developments in electrochemical water oxidationLyons, Michael E. G.; Doyle, Richard L.; Browne, Michelle P.; Godwin, Ian J.; Rovetta, Aurelie A. S.Current Opinion in Electrochemistry (2017), 1 (1), 40-45CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)A review Recent developments in electrochem. water oxidn. in aq. alk. soln. at earth abundant transition metal oxyhydroxide thin film electrodes are outlined and candidate high activity materials identified. The mol. mechanism of oxygen evolution at these oxide surfaces is discussed.
- 7Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J.-P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Oxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability. Catal. Today 2016, 262, 170– 180, DOI: 10.1016/j.cattod.2015.08.014Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVCnu7%252FE&md5=4bf7a1f1ee5806594ba98f8c86990ebeOxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stabilityCherevko, Serhiy; Geiger, Simon; Kasian, Olga; Kulyk, Nadiia; Grote, Jan-Philipp; Savan, Alan; Shrestha, Buddha Ratna; Merzlikin, Sergiy; Breitbach, Benjamin; Ludwig, Alfred; Mayrhofer, Karl J. J.Catalysis Today (2016), 262 (), 170-180CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Metallic iridium and ruthenium as well as their oxides are among the most active oxygen evolution (OER) electrocatalysts in acidic media, and are also of interest for the catalysis of the hydrogen evolution (HER). The stability of these materials under different operating conditions is, however, still not fully understood. In the current work, activity and stability of well-defined Ru, RuO2, Ir, and IrO2 thin film electrodes are evaluated in acidic and alk. electrolytes using an electrochem. scanning flow cell (SFC) connected to an inductively coupled plasma mass spectrometer (ICP-MS). Identical exptl. protocols are intentionally employed for all electrodes and electrolytes, to obtain unambiguous and comparable information on intrinsic activity and stability of the electrodes. It is found that independent of the electrolyte, OER activity decreases as Ru > Ir ≈ RuO2 > IrO2, while dissoln. increases as IrO2 « RuO2 < Ir « Ru. Moreover, dissoln. of these metals in both solns. is 2-3 orders of magnitude higher compared to their resp. oxides, and dissoln. is generally more intense in alk. solns. Similarly to the OER, metallic electrodes are more active catalysts for HER. They, however, suffer from dissoln. during native oxide redn., while IrO2 and RuO2 do not exhibit significant dissoln. The obtained results on activity and stability of the electrodes are discussed in light of their potential applications, i.e. water electrolyzers or fuel cells.
- 8Sayeed, M. A.; Herd, T.; O’Mullane, A. P. Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reaction. J. Mater. Chem. A 2016, 4, 991– 999, DOI: 10.1039/C5TA09125JGoogle Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFCksrzF&md5=359981ff1f1ea951c643f7d66003ea67Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reactionSayeed, Md Abu; Herd, Tenille; O'Mullane, Anthony P.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (3), 991-999CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)The oxides of Co have recently been shown to be highly effective electrocatalysts for the O evolution reaction (OER) under alk. conditions. In general species such as Co3O4 and CoOOH were studied that often require an elevated temp. step during their synthesis to create cryst. materials. The authors study the rapid and direct electrochem. formation of amorphous nanostructured Co(OH)2 on Au electrodes under room temp. conditions which is a highly active precursor for the OER. During the OER some conversion to cryst. Co3O4 occurs at the surface, but the bulk of the material remains amorphous. The underlying Au electrode is crucial to the materials enhanced performance and provides higher c.d. than can be achieved using C, Pd or Cu support electrodes. This catalyst exhibits excellent activity with a c.d. of 10 mA cm-2 at an overpotential of 360 mV with a high turnover frequency of 2.1 s-1 in 1 M NaOH. A Tafel slope of 56 mV dec-1 at low overpotentials and a slope of 122 mV dec-1 at high overpotentials is consistent with the dual barrier model for the electrocatalytic evolution of O. Significantly, the catalyst maintains excellent activity for up to 24 h of continuous operation and this approach offers a facile way to create a highly effective and stable material.
- 9Pei, Y.; Yang, Y.; Zhang, F.; Dong, P.; Baines, R.; Ge, Y.; Chu, H.; Ajayan, P. M.; Shen, J.; Ye, M. Controlled Electrodeposition Synthesis of Co–Ni–P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water Splitting. ACS Appl. Mater. Interfaces 2017, 9, 31887– 31896, DOI: 10.1021/acsami.7b09282Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtl2lsLfO&md5=021895e827a87dcce863c4d5463297d3Controlled Electrodeposition Synthesis of Co-Ni-P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water SplittingPei, Yu; Yang, Yang; Zhang, Fangfang; Dong, Pei; Baines, Robert; Ge, Yuancai; Chu, Hang; Ajayan, Pulickel M.; Shen, Jianfeng; Ye, MingxinACS Applied Materials & Interfaces (2017), 9 (37), 31887-31896CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Synthesis of highly efficient and robust catalysts with earth-abundant resources for overall water splitting is essential for large-scale energy conversion processes. Herein, a series of highly active and inexpensive Co-Ni-P films were fabricated by a one-step const. c.d. electrodeposition method. These films were demonstrated to be efficient bifunctional catalysts for both H2 and O2 evolution reactions (HER and OER), while deposition time was deemed to be the crucial factor governing electrochem. performance. At the optimal deposition time, the obtained Co-Ni-P-2 catalyst performed remarkably for both HER and OER in alk. media. In particular, it requires -103 mV overpotential for HER and 340 mV for OER to achieve the c.d. of 10 mA cm-2, with corresponding Tafel slopes of 33 and 67 mV dec-1. Moreover, it outperforms the Pt/C//RuO2 catalyst and only needs -160 mV (430 mV) overpotential for HER (OER) to achieve 200 mA cm-2 c.d. Co-Ni-P electrodes were also conducted for the proof-of-concept exercise, which were proved to be flexible, stable, and efficient, further opening a new avenue for rapid synthesis of efficient, flexible catalysts for renewable energy resources.
- 10Escudero-Escribano, M.; Pedersen, A. F.; Paoli, E. A.; Frydendal, R.; Friebel, D.; Malacrida, P.; Rossmeisl, J.; Stephens, I. E. L.; Chorkendorff, I. Importance of Surface IrOx in Stabilizing RuO2 for Oxygen Evolution. J. Phys. Chem. B 2018, 122, 947– 955, DOI: 10.1021/acs.jpcb.7b07047Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1yhtr3I&md5=94ceca236e222c41ee1f08e8c9f73a22Importance of Surface IrOx in Stabilizing RuO2 for Oxygen EvolutionEscudero-Escribano, Maria; Pedersen, Anders F.; Paoli, Elisa A.; Frydendal, Rasmus; Friebel, Daniel; Malacrida, Paolo; Rossmeisl, Jan; Stephens, Ifan E. L.; Chorkendorff, IbJournal of Physical Chemistry B (2018), 122 (2), 947-955CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)The high precious metal loading and high overpotential of the oxygen evolution reaction (OER) prevents the widespread use of polymer electrolyte membrane (PEM) water electrolyzers. Herein the authors explore the OER activity and stability in acidic electrolyte of a combined IrOx/RuO2 system consisting of RuO2 thin films with submonolayer (1, 2, and 4 Å) amts. of IrOx deposited on top. Operando extended x-ray absorption fine structure (EXAFS) on the Ir L-3 edge revealed a rutile type IrO2 structure with some Ir sites occupied by Ru, IrOx being at the surface of the RuO2 thin film. The authors monitor corrosion on IrOx/RuO2 thin films by combining electrochem. quartz crystal microbalance (EQCM) with inductively coupled mass spectrometry (ICP-MS). The authors elucidate the importance of submonolayer surface IrOx in minimizing Ru dissoln. The authors can tune the surface properties of active OER catalysts, such as RuO2, aiming to achieve higher electrocatalytic stability in PEM electrolyzers.
- 11Browne, M. P.; O’Rourke, C.; Mills, A. A mechanical, high surface area and solvent-free ‘powder-to-electrode’ fabrication method for screening OER catalysts. Electrochem. Commun. 2017, 85, 1– 5, DOI: 10.1016/j.elecom.2017.10.011Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs12rsbvJ&md5=3e98b9f2cf64f9ca09f0f58885faa045A mechanical, high surface area and solvent-free 'powder-to-electrode' fabrication method for screening OER catalystsBrowne, M. P.; O'Rourke, C.; Mills, A.Electrochemistry Communications (2017), 85 (), 1-5CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)The screening of new OER materials routinely involves fabricating electrodes from powders using methods which are often time consuming and may involve using solvents and/or conductive materials that can alter the OER activity of the powder. Herein, a new mech., solvent-free method for fabricating electrodes for OER is described in which a electroactive material under test, mixed with a small amt. of PTFE powder (ca. 10 wt%), is pressed onto Pt powder to create a permanent, robust electrode that can be used in a rotating disc electrode set-up. This new method of fabricating electrodes is compared to the well-known dropcast on Glassy Carbon (GC) method, using com. available materials: RuO2, Co3O4 and NiO. The results show that the mech. route produces much better OER performances, in terms of overpotential and stability, for the com. metal oxide on the pressed disks when compared to the dropcast GC method. Finally, it is shown that this mech., high surface area, solvent-free electrode fabrication technique can also be achieved using silver, rather than platinum, as the conducting, support material.
- 12Stoerzinger, K. A.; Qiao, L.; Biegalski, M. D.; Shao-Horn, Y. Orientation-Dependent Oxygen Evolution Activities of Rutile IrO2 and RuO2. J. Phys. Chem. Lett. 2014, 5, 1636– 1641, DOI: 10.1021/jz500610uGoogle Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXms1Wiu7o%253D&md5=d40da2689df2faa48ad9dea72b21e7d6Orientation-Dependent Oxygen Evolution Activities of Rutile IrO2 and RuO2Stoerzinger, Kelsey A.; Qiao, Liang; Biegalski, Michael D.; Yang, Shao-HornJournal of Physical Chemistry Letters (2014), 5 (10), 1636-1641CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The activities of the O evolution reaction (OER) on IrO2 and RuO2 catalysts are among the highest known to date. However, the intrinsic OER activities of surfaces with defined crystallog. orientations are not well-established exptl. Here the authors report that the (100) surface of IrO2 and RuO2 is more active in alk. environments (pH 13) than the most thermodynamically stable (110) surface. The OER activity was correlated with the d. of coordinatively undersatd. metal sites of each crystallog. facet. The surface-orientation-dependent activities can guide the design of nanoscale catalysts with increased activity for electrolyzers, metal-air batteries, and photoelectrochem. H2O splitting applications.
- 13Gao, X.; Zhang, H.; Li, Q.; Yu, X.; Hong, Z.; Zhang, X.; Liang, C.; Lin, Z. Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water-Splitting. Angew. Chem., Int. Ed. 2016, 55, 6290– 6294, DOI: 10.1002/anie.201600525Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvVagtL0%253D&md5=f5b3ef8828f660655706b7230daff9bfHierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water-SplittingGao, Xuehui; Zhang, Hongxiu; Li, Quanguo; Yu, Xuegong; Hong, Zhanglian; Zhang, Xingwang; Liang, Chengdu; Lin, ZhanAngewandte Chemie, International Edition (2016), 55 (21), 6290-6294CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alk. electrolyte may improve the efficiency of overall water splitting. Nickel cobaltite (NiCo2O4) has been considered a promising electrode material for the OER. However, NiCo2O4 that can be used as an electrocatalyst in HER has not been studied yet. Herein, we report self-assembled hierarchical NiCo2O4 hollow microcuboids for overall water splitting including both the HER and OER reactions. The NiCo2O4 electrode shows excellent activity toward overall water splitting, with 10 mA/cm2 water-splitting current reached by applying just 1.65 V and 20 mA/cm2 by applying just 1.74 V across the two electrodes. The synthesis of NiCo2O4 microflowers confirms the importance of structural features for high-performance overall water splitting.
- 14Etzi Coller Pascuzzi, M.; Goryachev, A.; Hofmann, J. P.; Hensen, E. J. M. Mn promotion of rutile TiO2-RuO2 anodes for water oxidation in acidic media. Appl. Catal., B 2020, 261, 118225 DOI: 10.1016/j.apcatb.2019.118225Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFWisLfN&md5=78d8e8cb9ccfa1096c2e55b65e27c5bfMn promotion of rutile TiO2-RuO2 anodes for water oxidation in acidic mediaEtzi Coller Pascuzzi, Marco; Goryachev, Andrey; Hofmann, Jan P.; Hensen, Emiel J. M.Applied Catalysis, B: Environmental (2020), 261 (), 118225CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)A method to reduce noble metal content in oxygen-evolving electrocatalysts suitable to work in acidic media is presented. TiO2-RuO2 anodes can be promoted by Mn, resulting in increased activity and stability. The most active compn. displayed an overpotential of 386 mV at a c.d. of 10 mA cm-2, and a Tafel slope of 50 mV dec-1. This anode only included 17 at% Ru out of the total amt. of metals included in the film. We investigated the influence of Mn addn. to TiO2-RuO2 on the structure, morphol., and surface area, and related differences to catalytic activity and stability. We found that increased porosity of the anode film by Mn addn. and Mn inclusion in the TiO2-RuO2 lattice can explain the enhanced catalytic activity. A detailed characterization of fresh and used anodes provided insight into structural modifications induced by electrochem. treatment.
- 15Browne, M. P.; Nolan, H.; Duesberg, G. S.; Colavita, P. E.; Lyons, M. E. G. Low-Overpotential High-Activity Mixed Manganese and Ruthenium Oxide Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media. ACS Catal. 2016, 6, 2408– 2415, DOI: 10.1021/acscatal.5b02069Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjsFaqu7g%253D&md5=13dc3e0b2e3172da1c795162d00e5c53Low-Overpotential High-Activity Mixed Manganese and Ruthenium Oxide Electrocatalysts for Oxygen Evolution Reaction in Alkaline MediaBrowne, Michelle P.; Nolan, Hugo; Duesberg, Georg S.; Colavita, Paula E.; Lyons, Michael E. G.ACS Catalysis (2016), 6 (4), 2408-2415CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Mixed Mn/Ru oxide thermally prepd. electrodes using different compns. of Mn and Ru precursor salts have been fabricated on Ti supports via thermal decompn. at two annealing temps. Subsequently, the oxygen evolution reaction (OER) activities of these electrodes were detd. A majority of the mixed Mn/Ru catalysts are highly active for the OER, exhibiting lower overpotential values compared to those of the state-of-the-art RuO2 and IrO2 type materials, when measured at a c.d. of 10 mA cm-2. These Mn/Ru oxide materials are also cheaper to produce than the aforementioned platinum group materials, therefore rendering the Mn/Ru materials more practical and economical. The Mn/Ru catalysts are also evaluated with respect to their Tafel slopes and turnover frequency nos. Interestingly, SEM reveals that the morphologies of the electrodes change to a mud-cracked morphol., similar to that of the RuO2, with minimal amts. of the Ru precursor salt added to the Mn salt. Fourier transform IR spectroscopy and X-ray diffraction show that the Mn material fabricated in this study at the two annealing temps. is largely Mn3O4, while the Ru material is predominately RuO2. XPS was also used to investigate the Mn and Ru compn. ratios in each of the films.
- 16Browne, M. P.; Nolan, H.; Twamley, B.; Duesberg, G. S.; Colavita, P. E.; Lyons, M. E. G. Thermally Prepared Mn2O3/RuO2/Ru Thin Films as Highly Active Catalysts for the Oxygen Evolution Reaction in Alkaline Media. ChemElectroChem 2016, 3, 1847– 1855, DOI: 10.1002/celc.201600370Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlalsLrK&md5=1dbd1790c02f97209a994920449c5066Thermally prepared Mn2O3 /RuO2/Ru thin films as highly active catalysts for the Oxygen Evolution Reaction in Alkaline MediaBrowne, Michelle; Nolan, Hugo; Twamley, Brendan; Duesberg, Georg; Colavita, Paula; Lyons, MichaelChemElectroChem (2016), 3 (11), 1847-1855CODEN: CHEMRA; ISSN:2196-0216. (Wiley-VCH Verlag GmbH & Co. KGaA)Herein, a thermal decompn. method was utilized to fabricate pure and mixed manganese and ruthenium oxides for catalysts in the Oxygen Evolution Reaction (OER). XPS and X-ray Diffraction (XRD) reveal the manganese and ruthenium species produced at the annealing temp. of 600 C to be Mn2O3 and RuO2/Ru, resp. A no. of the mixed Mn/Ru oxides exhibit overpotential values, at a c.d. of 10 mA cm-2, approx. 200 mV lower than previously reported for Mn2O3/RuO2 oxides for the OER, while the Mn 50 material exhibits similar overpotentials reported by RuO2. Turnover Frequency (TOF) nos. for the Mn/Ru oxides were also calcd. and the results show that the TOF values for some of these materials are higher than RuO2. XPS anal. indicates a change in chem. environment of the Mn/Ru materials which exhibit higher TOF values. Subsequently, the pure Ru 100 material, in this study, has a lower overpotential at 10mA cm-2, when compared to previously reported values in the literature for RuO2 in alk. media. This may be due to the presence of metallic Ru found in the film or the decrease in crystallite size, detd. by XRD. XPS anal. was also carried out after OER to help det. the order of activity for the materials in this work.
- 17Wu, Y.; Tariq, M.; Zaman, W. Q.; Sun, W.; Zhou, Z.; Yang, J. Bimetallic Doped RuO2 with Manganese and Iron as Electrocatalysts for Favorable Oxygen Evolution Reaction Performance. ACS Omega 2020, 5, 7342– 7347, DOI: 10.1021/acsomega.9b04237Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXlsVeqsrc%253D&md5=a33705b2555b4d9054938a039895e32fBimetallic Doped RuO2 with Manganese and Iron as Electrocatalysts for Favorable Oxygen Evolution Reaction PerformanceWu, Yiyi; Tariq, Muhammad; Zaman, Waqas Qamar; Sun, Wei; Zhou, Zhenhua; Yang, JiACS Omega (2020), 5 (13), 7342-7347CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)Synthesizing oxygen evolution reaction (OER) catalysts with enhanced activity by codoping has been proven to be a feasible approach for the efficient use of noble metals via renewing their basic intrinsic properties. In continuation of the research in codoping, we prep. a ruthenium-based bimetallic doped catalyst MnxFeyRu1-x-yO2 with an outstanding OER activity as compared to pure RuO2, one of the state-of-the-art OER catalysts. The synthesized codoped RuO2 with a Mn/Fe molar ratio of 1 reflected a Tafel slope of only 41 mV dec-1, which is appreciably lower than 64 mV dec-1 for pure RuO2. The XPS performed reveals that oxygen vacancy and manganese valency are the key factors of the OER activity for codoped catalysts.
- 18Lin, C.; Li, J.-L.; Li, X.; Yang, S.; Luo, W.; Zhang, Y.; Kim, S.-H.; Kim, D.-H.; Shinde, S. S.; Li, Y.-F.; Liu, Z.-P.; Jiang, Z.; Lee, J.-H. In-situ reconstructed Ru atom array on α-MnO2 with enhanced performance for acidic water oxidation. Nat. Catal. 2021, 4, 1012– 1023, DOI: 10.1038/s41929-021-00703-0Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislOltLbI&md5=fa482c87b1e994cc9f16c1955be6023aIn-situ reconstructed Ru atom array on α-MnO2 with enhanced performance for acidic water oxidationLin, Chao; Li, Ji-Li; Li, Xiaopeng; Yang, Shuai; Luo, Wei; Zhang, Yaojia; Kim, Sung-Hae; Kim, Dong-Hyung; Shinde, Sambhaji S.; Li, Ye-Fei; Liu, Zhi-Pan; Jiang, Zheng; Lee, Jung-HoNature Catalysis (2021), 4 (12), 1012-1023CODEN: NCAACP; ISSN:2520-1158. (Nature Portfolio)The development of acid-stable oxygen evolution reaction electrocatalysts is essential for high-performance water splitting. Here, we report an electrocatalyst with Ru-atom-array patches supported on α-MnO2 (Ru/MnO2) for the oxygen evolution reaction following a mechanism that involves only *O and *OH species as intermediates. This mechanism allows direct O-O radical coupling for O2 evolution. Ru/MnO2 shows high activity (161 mV at 10 mA cm-2) and outstanding stability with small degrdn. after 200 h operation, making it one of the best-performing acid-stable oxygen evolution reaction catalysts. Operando vibrational and mass spectroscopy measurements were performed to probe the reaction intermediates and gaseous products for validating the oxygen evolution reaction pathway. First-principles calcns. confirmed the cooperative catalysis mechanism with a reduced energy barrier. Time-dependent elemental anal. demonstrated the occurrence of the in-situ dynamic cation exchange reaction during the oxygen evolution reaction, which is the key for triggering the reconstruction of Ru atoms into the ordered array with high durability.
- 19Gorlin, Y.; Lassalle-Kaiser, B.; Benck, J. D.; Gul, S.; Webb, S. M.; Yachandra, V. K.; Yano, J.; Jaramillo, T. F. In situ X-ray absorption spectroscopy investigation of a bifunctional manganese oxide catalyst with high activity for electrochemical water oxidation and oxygen reduction. J. Am. Chem. Soc. 2013, 135, 8525– 8534, DOI: 10.1021/ja3104632Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXoslSqt74%253D&md5=65ec2e82e2a005e5b1985e30baf47054In Situ X-ray Absorption Spectroscopy Investigation of a Bifunctional Manganese Oxide Catalyst with High Activity for Electrochemical Water Oxidation and Oxygen ReductionGorlin, Yelena; Lassalle-Kaiser, Benedikt; Benck, Jesse D.; Gul, Sheraz; Webb, Samuel M.; Yachandra, Vittal K.; Yano, Junko; Jaramillo, Thomas F.Journal of the American Chemical Society (2013), 135 (23), 8525-8534CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)In situ x-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochem. systems, with the ability to elucidate the chem. nature of electrocatalysts under reaction conditions. The authors perform in situ XAS measurements on a bifunctional Mn oxide (MnOx) catalyst with high electrochem. activity for the O redn. reaction (ORR) and the O evolution reaction (OER). Using x-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), exposure to an ORR-relevant potential of 0.7 V vs. RHE produces a disordered MnII3,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs. RHE, relevant to the OER, the authors observe an oxidn. of ∼80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged MnII3,III,IIIO4. XAS and electrochem. characterization of two thin film catalysts with different MnOx thicknesses reveals no significant influence of thickness on the measured oxidn. states, at either ORR or OER potentials, but demonstrates that the OER activity scales with film thickness. Probably the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film. As the portion of the catalyst film that is most likely to be oxidized at the high potentials necessary for the OER is that which is closest to the electrolyte interface, the authors hypothesize that the MnIII,IV oxide, rather than MnII3,III,IIIO4, is the phase pertinent to the obsd. OER activity.
- 20Frydendal, R.; Seitz, L. C.; Sokaras, D.; Weng, T.-C.; Nordlund, D.; Chorkendorff, I.; Stephens, I. E. L.; Jaramillo, T. F. Operando investigation of Au-MnOx thin films with improved activity for the oxygen evolution reaction. Electrochim. Acta 2017, 230, 22– 28, DOI: 10.1016/j.electacta.2017.01.085Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjsVKnsbo%253D&md5=eab2e28132f27c7ad3c06783d8d9b220Operando investigation of Au-MnOx thin films with improved activity for the oxygen evolution reactionFrydendal, Rasmus; Seitz, Linsey C.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Nordlund, Dennis; Chorkendorff, Ib; Stephens, Ifan E. L.; Jaramillo, Thomas F.Electrochimica Acta (2017), 230 (), 22-28CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The electrochem. splitting of water holds great potential as a method for producing clean fuels by storing electricity from intermittent energy sources. The efficiency of such a process would be greatly facilitated by incorporating more active catalysts based on abundant materials for the oxygen evolution reaction. Manganese oxides are promising as catalysts for this reaction. Recent reports show that their activity can be drastically enhanced when modified with gold. Herein, we investigate highly active mixed Au-MnOx thin films for the oxygen evolution reaction, which exhibit more than five times improvement over pure MnOx. These films are characterized with operando X-ray Absorption Spectroscopy, which reveal that Mn assumes a higher oxidn. state under reaction conditions when Au is present. The magnitude of the enhancement is correlated to the size of the Au domains, where larger domains are the more beneficial.
- 21Lian, S.; Browne, M. P.; Domínguez, C.; Stamatin, S. N.; Nolan, H.; Duesberg, G. S.; Lyons, M. E. G.; Fonda, E.; Colavita, P. E. Template-free synthesis of mesoporous manganese oxides with catalytic activity in the oxygen evolution reaction. Sustainable Energy Fuels 2017, 1, 780– 788, DOI: 10.1039/C7SE00086CGoogle Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1Crs7bM&md5=31fa10223e399a8a6a4e3247c0e250f8Template-free synthesis of mesoporous manganese oxides with catalytic activity in the oxygen evolution reactionLian, Suoyuan; Browne, Michelle P.; Dominguez, Carlota; Stamatin, Serban N.; Nolan, Hugo; Duesberg, Georg S.; Lyons, Michael E. G.; Fonda, Emiliano; Colavita, Paula E.Sustainable Energy & Fuels (2017), 1 (4), 780-788CODEN: SEFUA7; ISSN:2398-4902. (Royal Society of Chemistry)Porous manganese carbonate was obtained via solvothermal synthesis using ethanol and urea. The manganese carbonate was subsequently used as a precursor to synthesize mesoporous manganese oxides via thermal treatments at three various temps. X-ray diffraction and Extended X-ray Absorption Fine Structure (EXAFS) results shows that γ-MnO2 is synthesized at 380 and 450°C while Mn2O3 is produced at the annealing temp. of 575°C. X-ray absorption spectra show that γ-MnO2 converts completely to Mn2O3 after annealing over the 450-575°C range. The oxides obtained at 380°C and 450°C possess extremely high sp. surface area, which is of interest for catalytic applications. The oxides were investigated as electrocatalysts for the oxygen evolution reaction; the oxide prepd. at the lowest annealing temp. was found to be the optimum catalyst with an overpotential of 427 ± 10 mV at a c.d. of 10 mA cm-2, normalized by the geometric area. The improved catalytic activity was related to the presence of defect-rich and highly porous manganese dioxide at the lowest annealing temp.
- 22Petrykin, V.; Bastl, Z.; Franc, J.; Macounova, K.; Makarova, M.; Mukerjee, S.; Ramaswamy, N.; Spirovova, I.; Krtil, P. Local Structure of Nanocrystalline Ru1–xNixO2–δ Dioxide and Its Implications for Electrocatalytic Behavior─An XPS and XAS Study. J. Phys. Chem. C 2009, 113, 21657– 21666, DOI: 10.1021/jp904935eGoogle Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsFSrsb3K&md5=d0c70fefe8e7ff11c0fc971919412b11Local Structure of Nanocrystalline Ru1-xNixO2-δ Dioxide and Its Implications for Electrocatalytic Behavior - An XPS and XAS StudyPetrykin, V.; Bastl, Z.; Franc, J.; Macounova, K.; Makarova, M.; Mukerjee, S.; Ramaswamy, N.; Spirovova, I.; Krtil, P.Journal of Physical Chemistry C (2009), 113 (52), 21657-21666CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Chem. compn., crystal structure, as well as short-range at. arrangement of nanocryst. Ru1-xNixO2-δ (x = 0.05, 0.1, 0.15, 0.2, 0.3) were studied using energy dispersive x-ray spectroscopy (EDX), XPS, and X-ray absorption spectroscopy (XAS). The prepd. materials form single-phase nanocrystals with rutile structure. Regardless of the chem. compn., the surface of Ru1-xNixO2-δ oxides is Ni-enriched with respect to overall chem. compn. According to both XPS and XANES, the oxidn. state of Ru remains +4 in the studied materials. Ni ions are present in both divalent and trivalent states with the fraction of trivalent ions decreasing with increasing Ni content. The refinement of local structure using EXAFS data based on Ru-K and Ni-K edge absorption spectra shows that Ru preserves local arrangement characteristic for Ru dioxide. The incorporated Ni shows a tendency to form clusters within a rutile structure for low Ni concn. At high Ni content, the architecture of the Ni-rich defects resembles architecture of shear planes in oxygen -deficient rutile. These Ni-rich regions likely manifest themselves on the surface as line or plane defects, which are the most likely structural features active in the electrocatalytic processes in oxygen and chlorine evolution.
- 23Seitz, L. C.; Nordlund, D.; Gallo, A.; Jaramillo, T. F. Tuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution Reaction. Electrochim. Acta 2016, 193, 240– 245, DOI: 10.1016/j.electacta.2016.01.200Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XivVCktbk%253D&md5=c981aa03865018ca6cf6068316ea2affTuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution ReactionSeitz, Linsey C.; Nordlund, Dennis; Gallo, Alessandro; Jaramillo, Thomas F.Electrochimica Acta (2016), 193 (), 240-245CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Understanding catalyst function to improve activity for the O evolution reaction (OER) is key to increasing the overall efficiency of electrochem. H2O splitting, a promising method for sustainable and clean prodn. of H. Using a straightforward and scalable sol-gel synthesis, the authors explore the effects of metal compn. in CoxTi1-xOy on electrochem. activity, at. structure, and electronic state. Phys. and electronic characterization reveal that increased amts. of Ti stabilize the 2+ oxidn. state of the Co precursor and give less active CoO-like catalysts. Conversely, films with Co:Ti ratios of 1:1 or greater result in catalysts with high activity, correlating with greater Co 3+ character, as measured by ex situ XAS for samples as-prepd. and after exposure to OER conditions. Addnl., decreasing the Ti content systematically shifts the Co redox potential from ∼1.5 V vs. RHE with a 1:3 Co:Ti ratio to 1.0 V vs. RHE with no Ti, further evidence that Ti stabilizes Co in a lower oxidn. state. Controlling the oxidn. state of metals in metal-oxide OER catalysts can have a profound effect on catalytic activity.
- 24Abbott, D. F.; Lebedev, D.; Waltar, K.; Povia, M.; Nachtegaal, M.; Fabbri, E.; Copéret, C.; Schmidt, T. J. Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from Operando XAS. Chem. Mater. 2016, 28, 6591– 6604, DOI: 10.1021/acs.chemmater.6b02625Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVeht7jM&md5=45b8a8fb48922d66af500be4bf9d2b59Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from Operando XASAbbott, Daniel F.; Lebedev, Dmitry; Waltar, Kay; Povia, Mauro; Nachtegaal, Maarten; Fabbri, Emiliana; Coperet, Christophe; Schmidt, Thomas J.Chemistry of Materials (2016), 28 (18), 6591-6604CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A current challenge faced in H2O electrolysis is the development of structure-activity relations for understanding and improving IrOx-based catalysts for the O evolution reaction (OER). The authors report a simple and scalable modified Adams fusion method for prepg. highly OER active, Cl-free Ir oxide nanoparticles of various size and shape. The applied approach allows for the effects of particle size, morphol., and the nature of the surface species on the OER activity of IrO2 to be studied. Ir oxide synthesized at 350° from Ir(acac)3, consisting of 1.7 ± 0.4 nm particles with a sp. surface area of 150 m2 g-1, shows the highest OER activity (E = 1.499 ± 0.003 V at 10 A gox-1). Operando x-ray absorption spectroscopy (XAS) and XPS studies indicate Ir hydroxo (Ir-OH) surface species, which are strongly linked to the OER activity. Prepn. of larger IrO2 particles using higher temps. results in a change of the particle morphol. from spherical to rod-shaped particles. A decrease of the intrinsic OER activity was assocd. with the predominant termination of the rod-shape particles by highly ordered (110) facets in addn. to limited diffusion within mesoporous features.
- 25Gorlin, Y.; Chung, C.-J.; Benck, J. D.; Nordlund, D.; Seitz, L.; Weng, T.-C.; Sokaras, D.; Clemens, B. M.; Jaramillo, T. F. Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation. J. Am. Chem. Soc. 2014, 136, 4920– 4926, DOI: 10.1021/ja407581wGoogle Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXkslalt7w%253D&md5=75bb3f8adb37fbebda812e48a79e4cd0Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water OxidationGorlin, Yelena; Chung, Chia-Jung; Benck, Jesse D.; Nordlund, Dennis; Seitz, Linsey; Weng, Tsu-Chien; Sokaras, Dimosthenis; Clemens, Bruce M.; Jaramillo, Thomas F.Journal of the American Chemical Society (2014), 136 (13), 4920-4926CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnO, a promising OER catalyst. We conclusively demonstrate that adding Au to MnO significantly enhances OER activity relative to MnO in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnO catalysts reported to date. We also provide evidence that it is a local rather than bulk interaction between Au and MnO that leads to the obsd. enhancement in the OER activity. Engineering improvements in nonprecious metal-based catalysts by the addn. of Au or other noble metals could still represent a scalable catalyst as even trace amts. of Au are shown to lead a significant enhancement in the OER activity of MnO.
- 26Petrykin, V.; Macounová, K.; Okube, M.; Mukerjee, S.; Krtil, P. Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolution. Catal. Today 2013, 202, 63– 69, DOI: 10.1016/j.cattod.2012.03.075Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XntVyrurw%253D&md5=b84968444c0e8740adb917cbb50e6005Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolutionPetrykin, Valery; Macounova, Katerina; Okube, Maki; Mukerjee, Sanjeev; Krtil, PetrCatalysis Today (2013), 202 (), 63-69CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Nano-particulate Co doped ruthenium dioxide electrocatalysts of the general formula Ru1-xCoxO2-y (0 < x 0.3) were prepd. by a co-pptn. method. The electrocatalysts with x < 0.2 conform to a single phase nano-cryst. materials. On the local level the Co forms clusters dispersed in the original rutile-like matrix. The local environment of the Co conforms to a rutile model which preserves the cationic arrangement but suppresses the probability of the Ru-Ru and Co-Co neighbors along the shortest metal-metal bonds. The electrocatalytic activity of the synthesized Ru1-xCoxO2-y materials in oxygen evolution is comparable with that of the non-doped ruthenium dioxide and little depends on the actual Co content. In presence of chlorides the Co doped materials are more selective towards oxygen evolution compared with the non doped ruthenia. The enhanced oxygen evolution in the case of Co doped electrocatalysts can be attributed to a chem. recombination of surface confined oxo-species. The selectivity shift towards oxygen evolution can be linked with limited activity of the Ru1-xCoxO2-y materials in the chlorine evolution reaction which seems to be relatively weakly dependent on the chloride concn.
- 27Petrykin, V.; Macounova, K.; Shlyakhtin, O. A.; Krtil, P. Tailoring the Selectivity for Electrocatalytic Oxygen Evolution on Ruthenium Oxides by Zinc Substitution. Angew. Chem., Int. Ed. 2010, 49, 4813– 4815, DOI: 10.1002/anie.200907128Google Scholar27https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXotVCgu7w%253D&md5=ac55be8552da19210ab83b7d01d96d70Tailoring the selectivity for electrocatalytic oxygen evolution on ruthenium oxides by zinc substitutionPetrykin, V.; Macounova, K.; Shlyakhtin, O. A.; Krtil, PetrAngewandte Chemie, International Edition (2010), 49 (28), 4813-4815, S4813/1-S4813/3CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The voltammetry results combined with differential electrochem. mass spectroscopy (DEMS) data show significant selectivity of the Ru-Zn-O oxides towards the oxygen-evolution reactions even in chloride-contg. systems.
- 28Biesinger, M. C.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn. Appl. Surf. Sci. 2010, 257, 887– 898, DOI: 10.1016/j.apsusc.2010.07.086Google Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtFOqsbrM&md5=b1ded0992b488ad83c6195c17c9ba4b9Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and ZnBiesinger, Mark C.; Lau, Leo W. M.; Gerson, Andrea R.; Smart, Roger St. C.Applied Surface Science (2010), 257 (3), 887-898CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)Chem. state x-ray photoelectron spectroscopic anal. of 1st row transition metals and their oxides and hydroxides is challenging due to the complexity of the 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. Current literature shows that all values necessary for reproducible, quant. chem. state anal. are usually not provided. A more consistent, practical and effective approach to curve-fitting the various chem. states in a variety of Sc, Ti, V, Cu and Zn metals, oxides and hydroxides is reported. The curve-fitting procedures proposed are based on a combination of (1) std. spectra from quality ref. samples, (2) a survey of appropriate literature databases and/or a compilation of the literature refs., and (3) specific literature refs. where fitting procedures are available. Binding energies, full-width at half max. (FWHM) values, spin-orbit splitting values, asym. peak-shape fitting parameters, and, for Cu and Zn, Auger parameters values are presented. The quantification procedure for Cu species details the use of the shake-up satellites for Cu(II)-contg. compds. and the exact binding energies of the Cu(0) and Cu(I) peaks. The use of the modified Auger parameter for Cu and Zn species allows for corroborating evidence when there is uncertainty in the binding energy assignment. These procedures can remove uncertainties in anal. of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.
- 29Newville, M. EXAFS analysis using FEFF and FEFFIT. J. Synchrotron Radiat. 2001, 8, 96– 100, DOI: 10.1107/S0909049500016290Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhs1amt7s%253D&md5=97e5f5081ebd6f0313b8462da7f7231bEXAFS analysis using FEFF and FEFFITNewville, MatthewJournal of Synchrotron Radiation (2001), 8 (2), 96-100CODEN: JSYRES; ISSN:0909-0495. (Munksgaard International Publishers Ltd.)Some of the advanced EXAFS anal. features of FEFF and FEFFIT are described. The scattering path formalism from FEFF and cumulant expansion are used as the basic building blocks of EXAFS anal., giving a flexible and robust parameterization of most EXAFS problems. The ability to model EXAFS data in terms of generalized phys. variables is shown, including the simultaneous refinement of 2 different polarizations for Co K EXAFS data of CoPt3.
- 30Newville, M. IFEFFIT: interactive XAFS analysis and FEFF fitting. J. Synchrotron Radiat. 2001, 8, 322– 324, DOI: 10.1107/S0909049500016964Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhs1als7c%253D&md5=38aec52f539e7522f80468400f90cef1IFEFFIT: interactive XAFS analysis and FEFF fittingNewville, MatthewJournal of Synchrotron Radiation (2001), 8 (2), 322-324CODEN: JSYRES; ISSN:0909-0495. (Munksgaard International Publishers Ltd.)IFEFFIT, an interactive program and scriptable library of XAFS algorithms is presented. The core algorithms of AUTOBK and FEFFIT were combined with general data manipulation and interactive graphics into a single package. IFEFFIT comes with a command-line program that can be run either interactively or in batch-mode. It also provides a library of functions that can be used easily from C or Fortran, as well as high level scripting languages such as Tcl, Perl and Python. Using this library, a Graphical User Interface for rapid 'online' data anal. is demonstrated. IFEFFIT is freely available with an Open Source license. Outside use, development, and contributions are encouraged.
- 31Diebold, U.; Madey, T. E. TiO2 by XPS. Surf. Sci. Spectra 1996, 4, 227– 231, DOI: 10.1116/1.1247794Google ScholarThere is no corresponding record for this reference.
- 32Di Castro, V.; Polzonetti, G. XPS study of MnO oxidation. J. Electron Spectrosc. Relat. Phenom. 1989, 48, 117– 123, DOI: 10.1016/0368-2048(89)80009-XGoogle Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXit1Cgsbg%253D&md5=f0e15920bae10142febdcd1bb0411f9fXPS study of manganese monoxide oxidationDi Castro, V.; Polzonetti, G.Journal of Electron Spectroscopy and Related Phenomena (1989), 48 (1-2), 117-23CODEN: JESRAW; ISSN:0368-2048.The oxidn. of a MnO layer was studied by XPS at 400°. Pure Mn oxides were measured for comparison and the Mn oxidn. states were identified by Mn2p binding energy, Mn2p satellite structure, Mn3s multiplet splitting and valence spectra. A progressive oxidn. of MnO to Mn2O3 without intermediate formation of Mn3O4 was obsd. Comparison of core and valence spectra indicates that a thin layer of Mn2O3 is initially formed on top of MnO. At higher O2 exposure the MnO is completely oxidized to Mn2O3.
- 33Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717– 2730, DOI: 10.1016/j.apsusc.2010.10.051Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXjtVWntw%253D%253D&md5=dcecf58a93c37118aa69743501f10816Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and NiBiesinger, Mark C.; Payne, Brad P.; Grosvenor, Andrew P.; Lau, Leo W. M.; Gerson, Andrea R.; Smart, Roger St. C.Applied Surface Science (2011), 257 (7), 2717-2730CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)Chem. state x-ray photoelectron spectroscopic anal. of 1st row transition metals and their oxides and hydroxides is challenging due to the complexity of their 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. The previous paper in which the authors examd. Sc, Ti, V, Cu and Zn species, showed that all the values of the spectral fitting parameters for each specific species, i.e. binding energy (eV), full wide at half max. (FWHM) value (eV) for each pass energy, spin-orbit splitting values and asym. peak shape fitting parameters, are not all normally provided in the literature and data bases, and are necessary for reproducible, quant. chem. state anal. A more consistent, practical and effective approach to curve fitting was developed based on a combination of (1) std. spectra from quality ref. samples, (2) a survey of appropriate literature databases and/or a compilation of literature refs. and (3) specific literature refs. where fitting procedures are available. This paper extends this approach to the chem. states of Cr, Mn, Fe, Co and Ni metals, and various oxides and hydroxides where intense, complex multiplet splitting in many of the chem. states of these elements poses unique difficulties for chem. state anal. The curve fitting procedures proposed use the same criteria as proposed previously but with the addnl. complexity of fitting of multiplet split spectra which was done based on spectra of numerous ref. materials and theor. XPS modeling of these transition metal species. Binding energies, FWHM values, asym. peak shape fitting parameters, multiplet peak sepn. and peak area percentages are presented. The procedures developed can be used to remove uncertainties in the anal. of surface states in nanoparticles, corrosion, catalysis and surface-engineered materials.
- 34Wöllner, A.; Lange, F.; Schmelz, H.; Knözinger, H. Characterization of mixed copper-manganese oxides supported on titania catalysts for selective oxidation of ammonia. Appl. Catal., A 1993, 94, 181– 203, DOI: 10.1016/0926-860X(93)85007-CGoogle ScholarThere is no corresponding record for this reference.
- 35Wei, Y. J.; Yan, L. Y.; Wang, C. Z.; Xu, X. G.; Wu, F.; Chen, G. Effects of Ni Doping on [MnO6] Octahedron in LiMn2O4. J. Phys. Chem. B 2004, 108, 18547– 18551, DOI: 10.1021/jp0479522Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXpt1Cqsbw%253D&md5=95352c741c029f57b6037a8b035c21f9Effects of Ni Doping on [MnO6] Octahedron in LiMn2O4Wei, Y. J.; Yan, L. Y.; Wang, C. Z.; Xu, X. G.; Wu, F.; Chen, G.Journal of Physical Chemistry B (2004), 108 (48), 18547-18551CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)LiNixMn2-xO4 (x ≤ 0.5) powders were synthesized using a sol-gel technique. Partial Ni atoms occupy the 8a sites in heavy doped LiNixMn2-xO4 via x-ray diffraction. XPS results showed an increase and a decrease in the av. valence state of Mn and Ni ions, resp., with the nickel content. Five Raman modes of LiNixMn2-xO4 were obsd. The A1g band was obsd. being shifted to higher frequency for x ≤ 0.2 and shifted to lower frequency for x > 0.2. The most rigid [MnO6] octahedron occurs at x = 0.2. [MnO6] octahedron in LiNi0.2Mn1.8O4 possesses the strongest rigidity with respect to the other LiNixMn2-xO4 (x < 0.5 and ≠ 0.2).
- 36Morgan, D. J. Resolving ruthenium: XPS studies of common ruthenium materials. Surf. Interface Anal. 2015, 47, 1072– 1079, DOI: 10.1002/sia.5852Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFehsr7J&md5=719e072bfc36ab8bc6c09d7f09240285Resolving ruthenium: XPS studies of common ruthenium materialsMorgan, David J.Surface and Interface Analysis (2015), 47 (11), 1072-1079CODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)XPS utilizing monochromatic Al Kα radiation has been employed to study metallic ruthenium and the catalytically and technol. important ruthenium compds. RuO2, RuCl3, Ru(NO)(NO3)3 and Ru(AcAc)3. The results improve on the accuracy of already published Ru(3d) binding energies, expand known Ru(3p) binding energies and also report spin-orbit splitting for the core levels. For RuO2, the difference between anhyd. and hydrated samples is explored, and the effect on curve fitting such spectra is discussed. Anal. of RuCl3 has allowed, for the first time, the pos. identification of Ru(OH)3 by XPS.
- 37Jiao, F.; Frei, H. Nanostructured manganese oxide clusters supported on mesoporous silica as efficient oxygen-evolving catalysts. Chem. Commun. 2010, 46, 2920– 2922, DOI: 10.1039/B921820CGoogle Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXksFOktbc%253D&md5=8b6ebf5f19915fa71b7ac271f92a5198Nanostructured manganese oxide clusters supported on mesoporous silica as efficient oxygen-evolving catalystsJiao, Feng; Frei, HeinzChemical Communications (Cambridge, United Kingdom) (2010), 46 (17), 2920-2922CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Nanostructured Mn oxide clusters supported on mesoporous silica KIT-6 were characterized for generation of O2 in aq. soln. under visible light using tris(2,2'-bipyridine)Ru2+ photosensitizer and S2O82+ electron acceptor.
- 38Farges, F. Ab initio and experimental pre-edge investigations of the Mn K-edge XANES in oxide-type materials. Phys. Rev. B 2005, 71, 155109 DOI: 10.1103/PhysRevB.71.155109Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjvVeqtL8%253D&md5=201379adc3b902475bcdcd817004be65Ab initio and experimental pre-edge investigations of the Mn K-edge XANES in oxide-type materialsFarges, FrancoisPhysical Review B: Condensed Matter and Materials Physics (2005), 71 (15), 155109/1-155109/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Mn K edge ab initio FEFF8.2 calcns. of the pre-edge features of the x-ray-absorption near-edge structure (XANES) region were undertaken for Mn-bearing oxide-type compds. The aim of the study is to provide a reliable method for detg. quant. and accurate redox and symmetry information for Mn. In agreement with multiplet calcns. by Glatzel and co-workers, FEFF8.2 predicts a doublet and a triplet for Mn(II) and Mn(III) in octahedral symmetry, resp., in agreement with high-resoln. XANES expts. Site distortion increases notably the contribution from dipolar transitions and, consequently, the pre-edge feature integrated area. An even more intense pre-edge feature is calcd. and measured for the Td symmetry (singletlike). For Mn(IV), a triplet is predicted and measured for the Oh symmetry. However, addnl. transitions are found in Mn(IV)-rich compds., that are related to metal-metal transitions. These transitions overlap strongly with the true pre-edge, making extn. of redox and symmetry information for Mn(IV) more challenging. However, a model of the pre-edge with pseudo-Voigt functions of fixed calcd. width (based on core-hole lifetime and exptl. resoln.) helps to sep. the contributions related to 1st-neighbor symmetry from those of the metal-metal pairs. Application to multivalent defective Mn oxide materials suggests that the pre-edge information varies linearly as a function of Mn redox state or symmetry but varies nonlinearly as a function of both parameters. Finally, the polymn. of the Mn networks can be estd. from the metal-metal transitions found in the pre-edge region.
- 39Ramírez, A.; Hillebrand, P.; Stellmach, D.; May, M. M.; Bogdanoff, P.; Fiechter, S. Evaluation of MnOx, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of Water. J. Phys. Chem. C 2014, 118, 14073– 14081, DOI: 10.1021/jp500939dGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXps1Wjsb0%253D&md5=bd3946f772340f9d4612c2fa1e54ff38Evaluation of MnOx, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of WaterRamirez, Alejandra; Hillebrand, Philipp; Stellmach, Diana; May, Matthias M.; Bogdanoff, Peter; Fiechter, SebastianJournal of Physical Chemistry C (2014), 118 (26), 14073-14081CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Different manganese oxide phases were prepd. as thin films to elucidate their structure-function relationship with respect to oxygen evolution in the process of water splitting. For this purpose, amorphous MnOx films anodically deposited on F:SnO2/glass and annealed at different temps. (to improve film adherence and crystallinity) were tested in neutral and alk. electrolytes. Differential electrochem. mass spectroscopy showed that the anodic current correlated well with the onset of the expected oxygen evolution, where in 1 M KOH, the anodic current of cryst. α-Mn2O3 films was detd. to onset at an overpotential (η) of 170 mVRHE (at J = 0.1 mA/cm2) with current densities of ca. 20 mA/cm2 at η = 570 mVRHE. Amorphous MnOx films heated at 573 K (MnOx-573 K) were found to improve their adherence to F:SnO2/glass substrate after heat treatment with a slight crystn. detected by Raman spectroscopy. The onset of water oxidn. of MnOx-573 K films was identified at η = 230 mVRHE (at J = 0.1 mA/cm2) with current densities of ca. 20 mA/cm2 at η = 570 mVRHE (1 M KOH). The least active of the investigated manganese oxides was Mn3O4 with an onset at η = 290 mVRHE (at J = 0.1 mA/cm2) and current densities of ca. 10 mA/cm2 at η = 570 mVRHE (1 M KOH). In neutral soln. (1 M KPi), a similar tendency was obsd. with the lowest overpotential found for α-Mn2O3 followed by MnOx-573 K and Mn3O4. XPS revealed that after electrochem. treatment, the surfaces of the manganese oxide electrodes exhibited oxidn. of Mn II and Mn III toward Mn IV under oxygen evolving conditions. In the case of α-Mn2O3 and MnOx-573 K, the manganese oxidn. was found to be reversible in KPi when switching the potential above and below the oxygen evolution reaction (OER) threshold potential. Furthermore, SEM (SEM) images displayed the presence of an amorphous phase on top of all manganese oxide films here tested after oxygen evolution. The results indicate that structural changes played an important role in the catalytic activity of the manganese oxides, in addn. to oxidn. states, a large variety of Mn-O bond lengths and a high concn. of oxygen point defects. Thus, compared to Mn3O4, cryst. α-Mn2O3 and MnOx-573 K are the most efficient catalyst for water oxidn. in the manganese-oxygen system.
- 40Mattelaer, F.; Bosserez, T.; Rongé, J.; Martens, J. A.; Dendooven, J.; Detavernier, C. Manganese oxide films with controlled oxidation state for water splitting devices through a combination of atomic layer deposition and post-deposition annealing. RSC Adv. 2016, 6, 98337– 98343, DOI: 10.1039/C6RA19188FGoogle Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1elsr%252FJ&md5=5cd3d443ea285849426fbed6611c13d4Manganese oxide films with controlled oxidation state for water splitting devices through a combination of atomic layer deposition and post-deposition annealingMattelaer, Felix; Bosserez, Tom; Ronge, Jan; Martens, Johan A.; Dendooven, Jolien; Detavernier, ChristopheRSC Advances (2016), 6 (100), 98337-98343CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Solar hydrogen devices combine the power of photovoltaics and water electrolysis to produce hydrogen in a hybrid form of energy prodn. To engineer these into integrated devices (i.e. a water splitting catalyst on top of a PV element), the need exists for thin film catalysts that are both transparent for solar light and efficient in water splitting. Manganese oxides have already been shown to exhibit good water splitting performance, which can be further enhanced by conformal coating on high surface-area structures. The latter can be achieved by at. layer deposition (ALD). However, to optimize the catalytic and transparency properties of the water splitting layer, an excellent control over the oxidn. state of the manganese in the film is required. So far MnO, Mn3O4 and MnO2 ALD have been shown, while Mn2O3 is the most promising catalyst. Therefore, we investigated the post-deposition oxidn. and redn. of MnO and MnO2 ALD films, and derived strategies to achieve every phase in the MnO-MnO2 range by tuning the ALD process and post-ALD annealing conditions. Thin film Mn2O3 is obtained by thermal redn. of ALD MnO2, without the need for oxidative high temp. treatments. The obtained Mn2O3 is examd. for solar water splitting devices, and compared to the as-deposited MnO2. Both thin films show oxygen evolution activity and good solar light transmission.
- 41Liu, F.; Shan, W.; Lian, Z.; Xie, L.; Yang, W.; He, H. Novel MnWOx catalyst with remarkable performance for low temperature NH3-SCR of NOx. Catal. Sci. Technol. 2013, 3, 2699– 2707, DOI: 10.1039/C3CY00326DGoogle Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVSltr%252FL&md5=420d6c8f60cfe5bb2c2d63acedd0adabNovel MnWOx catalyst with remarkable performance for low temperature NH3-SCR of NOxLiu, Fudong; Shan, Wenpo; Lian, Zhihua; Xie, Lijuan; Yang, Weiwei; He, HongCatalysis Science & Technology (2013), 3 (10), 2699-2707CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)A novel W promoted MnOx catalyst (MnWOx) was used for the selective catalytic redn. (SCR) of NOx with NH3 at low temps., with high deNOx efficiency from 60 to 250 °C under relatively high space velocity. The MnWOx catalyst showed a unique core-shell structure with Mn3O4 covered by Mn5O8 while Mn4+ species at the outer surface served as a real active phase for NH3-SCR. The W doping resulted in the smaller particle size of MnOx active phase, increased the surface acidity and facilitated the NO/NH3 oxidn., thus enhancing low temp. deNOx efficiency by promoting both Langmuir-Hinshelwood and Eley-Rideal reaction pathways. This novel catalyst is promising to be used in the deNOx process for flue gas after dust removal and desulfurization.
- 42Wiechen, M.; Zaharieva, I.; Dau, H.; Kurz, P. Layered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashion. Chem. Sci. 2012, 3, 2330– 2339, DOI: 10.1039/C2SC20226CGoogle Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XotFGrsrs%253D&md5=82b5cc3945282c1bb968398e38403f4aLayered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashionWiechen, Mathias; Zaharieva, Ivelina; Dau, Holger; Kurz, PhilippChemical Science (2012), 3 (7), 2330-2339CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)In reaction sequences for light driven water-splitting into H2 and O2, water-oxidn. is a crucial reaction step. In vivo, the process is catalyzed within a photoenzyme called photosystem II (PSII) by a μ-oxido CaMn4 cluster, the oxygen-evolving complex (OEC). The OEC is known to be virtually inactive if Ca2+ is removed from its structure. Activity can be restored not only by the addn. of Ca2+ but also Sr2+ ions. We have recently introduced layered calcium manganese oxides of the birnessite mineral family as functional synthetic model compds. for the OEC. Here, we present the syntheses of layered manganese oxides where we varied the interlayer cations, prepg. a series of K-, Ca-, Sr- and Mg-contg. birnessites. Structural motifs within these materials were detd. using X-ray absorption spectroscopy (XAS) showing that all materials have similar at. structures despite their different elemental compns. Water-oxidn. expts. were carried out to elucidate structure-reactivity relations. These expts. demonstrated that the oxides-like the OEC-require the presence of calcium in their structures to reach max. catalytic activity. As another similarity to the OEC, Sr2+ is the "second best choice" for the secondary cation. The results thus support mechanistic proposals which involve an important catalytic role for Ca2+ in biol. water-oxidn. Addnl., they offer valuable hints for the development of synthetic, manganese-based water-oxidn. catalysts for artificial photosynthesis.
- 43Zahoransky, T.; Wegorzewski, A. V.; Huong, W.; Mikutta, C. X-ray absorption spectroscopy study of Mn reference compounds for Mn speciation in terrestrial surface environments. Am. Mineral. 2023, 108, 847– 864, DOI: 10.2138/am-2022-8236Google ScholarThere is no corresponding record for this reference.
- 44Grangeon, S.; Lanson, B.; Miyata, N.; Tani, Y.; Manceau, A. Structure of nanocrystalline phyllomanganates produced by freshwater fungi. Am. Mineral. 2010, 95, 1608– 1616, DOI: 10.2138/am.2010.3516Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFSnsr3P&md5=0e7827b11ebade165c9092f0a9cbf5e3Structure of nanocrystalline phyllomanganates produced by freshwater fungiGrangeon, Sylvain; Lanson, Bruno; Miyata, Naoyuki; Tani, Yukinori; Manceau, AlainAmerican Mineralogist (2010), 95 (11-12), 1608-1616CODEN: AMMIAY; ISSN:0003-004X. (Mineralogical Society of America)The crystal structures of biogenic Mn oxides produced by three fungal strains isolated from stream pebbles were detd. using chem. analyses, XANES and EXAFS spectroscopy, and powder X-ray diffraction. The fungi-mediated oxidn. of aq. Mn2+ produces layered Mn oxides analogous to vernadite, a natural nanostructured and turbostratic variety of birnessite. The crystallites have domain dimensions of ∼10 nm in the layer plane (equiv. to ∼35 MnO6 octahedra), and ∼1.5-2.2 nm perpendicularly (equiv. to ∼2-3 layers), on av. The layers have hexagonal symmetry and from 22 to 30% vacant octahedral sites. This proportion likely includes edge sites, given the extremely small lateral size of the layers. The layer charge deficit, resulting from the missing layer Mn4+ cations, is balanced mainly by interlayer Mn3+ cations in triple-corner sharing position above and/or below vacant layer octahedra. The high surface area, defective crystal structure, and mixed Mn valence confer to these bio-minerals an extremely high chem. reactivity. They serve in the environment as sorption substrate for trace elements and possess catalytic redox properties.
- 45Zhang, A.; Zhao, R.; Hu, L.; Yang, R.; Yao, S.; Wang, S.; Yang, Z.; Yan, Y.-M. Adjusting the Coordination Environment of Mn Enhances Supercapacitor Performance of MnO2. Adv. Energy Mater. 2021, 11, 2101412 DOI: 10.1002/aenm.202101412Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVOku7zO&md5=ac9cf687f4a10228c82c3994eeffde60Adjusting the Coordination Environment of Mn Enhances Supercapacitor Performance of MnO2Zhang, Anqi; Zhao, Rui; Hu, Lingyuan; Yang, Ru; Yao, Shuyun; Wang, Shiyu; Yang, Zhiyu; Yan, Yi-MingAdvanced Energy Materials (2021), 11 (32), 2101412CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)The electrochem. properties of transition metal oxides strongly depend on the coordination environment of metal atoms. Nevertheless, the relationship between the coordination environment of metal atoms and electrochem. performance of metal oxides is unclear, while the strategy of adjusting the coordination environment of metal atoms is rare. Herein, the engineering of the coordination environment of Mn atoms in manganese dioxides (MnO2) by using a triethanolamine (TEA) complex-induced method is reported. The detailed exptl. characterizations and d. functional theory calcns. show that the optimized Mn coordination environment with oxygen deficiency and more corner-shared Mn-Mn shells results in apparent electron dislocation and forms an effective built-in elec. field. As a result, the obtained MnO2-TEA sample exhibits a high cond. and an excellent ion diffusion capacity, with a remarkable specific capacitance of 417.5 F g-1 at 1 A g-1. At the power d. of 450.0 W kg-1, the fabricated asym. supercapacitor delivers the maximal energy d. (57.4 Wh kg-1). This work not only provides an effective strategy of adjusting the coordination environment of metal atoms in metal oxides, but also presents a deeper understanding of the electronic structure dependent electrochem. performance of electrode materials.
- 46Gaillot, A.-C.; Flot, D.; Drits, V. A.; Manceau, A.; Burghammer, M.; Lanson, B. Structure of Synthetic K-rich Birnessite Obtained by High-Temperature Decomposition of KMnO4. I. Two-Layer Polytype from 800 °C Experiment. Chem. Mater. 2003, 15, 4666– 4678, DOI: 10.1021/cm021733gGoogle Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXoslWiurY%253D&md5=f050e4ffd26e1c9a5c6e62e63ec09110Structure of Synthetic K-rich Birnessite Obtained by High-Temperature Decomposition of KMnO4. I. Two-Layer Polytype from 800 °C ExperimentGaillot, Anne-Claire; Flot, David; Drits, Victor A.; Manceau, Alain; Burghammer, Manfred; Lanson, BrunoChemistry of Materials (2003), 15 (24), 4666-4678CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The structure of a synthetic K birnessite (KBi) obtained as a finely dispersed powder by thermal decompn. of KMnO4 at 800° was for the 1st time studied by single-crystal XRD. KBi has a two-layer cell with a 2.840(1) and c 14.03(1) Å and space group P63/mmc. At. coordinates are given. In contrast to the structure model proposed by Kim et al. (Chem. Mater. 1999, 11, 557-563), the refined model demonstrates the sole presence of Mn4+ in the octahedral layers, the presence of 0.12 vacant layer sites per octahedron being responsible for the layer charge deficit. In agreement with x-ray absorption spectroscopy result, this layer charge deficit is compensated (1) by the presence of interlayer Mn3+ above or below vacant layer octahedra sharing three Olayer atoms with neighboring Mnlayer octahedra to form a triple-corner surface complex (VITC sites) and (2) by the presence of interlayer K in prismatic cavities located above or below empty tridentate cavities, sharing three edges with neighboring Mnlayer octahedra (VITE sites). As compared to the structure model proposed by Kim et al., this VITE site is shifted from the center of the prismatic cavity toward its edges. A complementary powder XRD study confirmed the structure model of the main defect-free KBi phase and allowed for the detn. of the nature of the stacking disorder in a defective accessory KBi phase admixed to the defect-free KBi.
- 47Krause, M. O.; Oliver, J. H. Natural widths of atomic K and L levels, Kα X-ray lines and several KLL Auger lines. J. Phys. Chem. Ref. Data 1979, 8, 329– 338, DOI: 10.1063/1.555595Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1MXks1Gmu78%253D&md5=37bd4bfc06afcd12790698af09afd916Natural widths of atomic K and L levels, Kα x-ray lines and several KLL Auger linesKrause, M. O.; Oliver, J. H.Journal of Physical and Chemical Reference Data (1979), 8 (2), 329-38CODEN: JPCRBU; ISSN:0047-2689.Semi-empirical values of the natural widths of K, L1, L2 and L3 levels, and Kα2 x-ray lines, and KL1L1, KL1L2 and KL2L3 Auger lines for the elements 10 ≤ Z ≤ 110 are presented in tables and graphs. Level width Γi (i = K, L1, L2, L3) is obtained from the relation Γi = ΓR,i/ωi, using the theor. radiative rate ΓR,i from Scofield's relativistic, relaxed Hartree-Fock calcn. and the fluorescence yield ωi from Krause's evaluation. X-ray and Auger line widths are calcd. as the sums of pertinent level widths. This tabulation of natural level and line widths is internally consistent, and is compatible with all relevant exptl. and theor. information. Present semi-empirical widths, esp. those of Kα1 and Kα2 x-rays, are compared with measured widths. Uncertainties of semi-empirical values are estd.
- 48Otoyama, M.; Jacquet, Q.; Iadecola, A.; Saubanère, M.; Rousse, G.; Tarascon, J.-M. Synthesis and Electrochemical Activity of Some Na(Li)-Rich Ruthenium Oxides with the Feasibility to Stabilize Ru6+. Adv. Energy Mater. 2019, 9, 1803674 DOI: 10.1002/aenm.201803674Google ScholarThere is no corresponding record for this reference.
- 49McKeown, D. A.; Hagans, P. L.; Carette, L. P. L.; Russell, A. E.; Swider, K. E.; Rolison, D. R. Structure of Hydrous Ruthenium Oxides: Implications for Charge Storage. J. Phys. Chem. B 1999, 103, 4825– 4832, DOI: 10.1021/jp990096nGoogle Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjtFOlt78%253D&md5=1d15e92817fcf2876d9834be01d94588Structure of Hydrous Ruthenium Oxides: Implications for Charge StorageMcKeown, David A.; Hagans, Patrick L.; Carette, Linda P. L.; Russell, Andrea E.; Swider, Karen E.; Rolison, Debra R.Journal of Physical Chemistry B (1999), 103 (23), 4825-4832CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)Hydrous ruthenium oxide (RuO2·xH2O or RuOxHy) is a mixed electron-proton conductor with a specific capacitance as high as 720 F/g/proton, making it a candidate material for energy storage. The correlation between the structure and properties of RuO2·xH2O materials is not well understood due to their amorphous nature and compositional variability. In this study, ruthenium oxides with the compns. RuO2·2.32H2O, RuO2·0.29H2O, and anhyd. RuO2 are characterized using thermogravimetric anal. (TGA), X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES) and extended X-ray fine structure (EXAFS) analyses. XANES cannot be used to distinguish between Ru(III) and Ru(IV) in the hydrous oxides, but the EXAFS analyses show large differences in the short-range structures of the materials. Whereas anhyd. RuO2 has the rutile structure comprising chains of RuO6 octahedra linked in three dimensions, the structure of RuO2·0.29H2O is rutile-like at the RuO6 core, but less connected and progressively disordered beyond the RuO6 core. The structure of RuO2·2.32H2O is composed of chains of disordered RuO6 octahedra that exhibit no chain-to-chain linking or three-dimensional order. Although the local structures of RuO2·0.29H2O and RuO2·2.32H2O markedly differ, their specific capacitances are large and essentially equiv., so nonunique local structures can balance effective electron transport (along dioxo bridges) with the effective proton transport (through structural water) necessary for charge storage.
- 50Qiu, J.-Z.; Hu, J.; Lan, J.; Wang, L.-F.; Fu, G.; Xiao, R.; Ge, B.; Jiang, J. Pure Siliceous Zeolite-Supported Ru Single-Atom Active Sites for Ammonia Synthesis. Chem. Mater. 2019, 31, 9413– 9421, DOI: 10.1021/acs.chemmater.9b03099Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitVOhsbbN&md5=247ff05f5ff8753e62044ea90a77218bPure Siliceous Zeolite-Supported Ru Single-Atom Active Sites for Ammonia SynthesisQiu, Jiang-Zhen; Hu, Jibo; Lan, Jinggang; Wang, Long-Fei; Fu, Guangying; Xiao, Rujian; Ge, Binghui; Jiang, JiuxingChemistry of Materials (2019), 31 (22), 9413-9421CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)As the most active new frontier, a single-atom catalyst (SAC) combining the merits of heterogeneous and homogeneous catalysts would have a significant effect on a 100-yr history of ammonia synthesis research. It is commonly accepted that B5 is the active site of Ru catalysts for ammonia synthesis. Here, the Ru single atoms catalyst has been demonstrated active and efficient for ammonia synthesis. To this end, an ideal model catalyst, pure siliceous zeolite-supported Ru SAC (Ru SAs/S-1), which shows surprising catalytic ammonia synthesis activity compared to that of a conventional Ru catalyst was designed. Both at. resoln. scanning transmission electron microscopy and X-ray absorption spectrometric anal. identify the single-Ru-atom nature of Ru SAs/S-1 before and after the reaction. Further DFT calcns. reveal that the reaction mechanism is different from traditional mechanisms. Therefore, beyond B5 sites, this paper provides an alternative SAC strategy to design high-performance Ru catalysts for ammonia synthesis.
- 51Matheu, R.; Ertem, M. Z.; Gimbert-Suriñach, C.; Sala, X.; Llobet, A. Seven Coordinated Molecular Ruthenium–Water Oxidation Catalysts: A Coordination Chemistry Journey. Chem. Rev. 2019, 119, 3453– 3471, DOI: 10.1021/acs.chemrev.8b00537Google Scholar51https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjslyhurY%253D&md5=8013afd52a89cac003d9fa035a073cb9Seven Coordinated Molecular Ruthenium-Water Oxidation Catalysts: A Coordination Chemistry JourneyMatheu, Roc; Ertem, Mehmed Z.; Gimbert-Surinach, Carolina; Sala, Xavier; Llobet, AntoniChemical Reviews (Washington, DC, United States) (2019), 119 (6), 3453-3471CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Mol. H2O oxidn. catalysis is a field that has experienced an impressive development over the past decade mainly fueled by the promise of generation of sustainable C neutral fuel society, based on H2O splitting. Most of these advancements were possible thanks to the detailed understanding of the reactions and intermediates involved in the catalytic cycles. Today's best mol. H2O oxidn. catalysts reach turnover frequencies that are orders of magnitude higher than that of natural O evolving center in photosystem II. These catalysts are based on Ru complexes where at some stage, the 1st coordination sphere of the metal center becomes 7 coordinated. The key for this achievement is largely based on the use of adaptative ligands that adjust their coordination mode depending on the structural and electronic demands of the metal center at different oxidn. states accessed within the catalytic cycle. This Review covers the latest and most significant developments on Ru complexes that behave as powerful H2O oxidn. catalysts and where at some stage the Ru metal attains coordination no. 7. It provides a comprehensive and rational understanding of the different structural and electronic factors that govern the behavior of these catalysts.
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References
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- 1Zeng, K.; Zhang, D. Recent progress in alkaline water electrolysis for hydrogen production and applications. Prog. Energy Combust. Sci. 2010, 36, 307– 326, DOI: 10.1016/j.pecs.2009.11.0021https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXis1OqtLw%253D&md5=fb3b70cabefcb81fd4fc2ab3a228a3fbRecent progress in alkaline water electrolysis for hydrogen production and applicationsZeng, Kai; Zhang, DongkeProgress in Energy and Combustion Science (2010), 36 (3), 307-326CODEN: PECSDO; ISSN:0360-1285. (Elsevier Ltd.)A review. Alk. water electrolysis is one of the easiest methods for hydrogen prodn., offering the advantage of simplicity. The challenges for widespread use of water electrolysis are to reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. This literature review examines the current state of knowledge and technol. of hydrogen prodn. by water electrolysis and identifies areas where R&D effort is needed in order to improve this technol. Following an overview of the fundamentals of alk. water electrolysis, an elec. circuit analogy of resistances in the electrolysis system is introduced. The resistances are classified into three categories, namely the elec. resistances, the reaction resistances and the transport resistances. This is followed by a thorough anal. of each of the resistances, by means of thermodn. and kinetics, to provide a scientific guidance to minimising the resistance in order to achieve a greater efficiency of alk. water electrolysis. The thermodn. anal. defines various electrolysis efficiencies based on theor. energy input and cell voltage, resp. These efficiencies are then employed to compare different electrolysis cell designs and to identify the means to overcome the key resistances for efficiency improvement. The kinetic anal. reveals the dependence of reaction resistances on the alk. concn., ion transfer, and reaction sites on the electrode surface, the latter is detd. by the electrode materials. A quant. relationship between the cell voltage components and c.d. is established, which links all the resistances and manifests the importance of reaction resistances and bubble resistances. The important effect of gas bubbles formed on the electrode surface and the need to minimise the ion transport resistance are highlighted. The historical development and continuous improvement in the alk. water electrolysis technol. are examd. and different water electrolysis technologies are systematically compared using a set of the practical parameters derived from the thermodn. and kinetic analyses. In addn. to the efficiency improvements, the needs for redn. in equipment and maintenance costs, and improvement in reliability and durability are also established. The future research needs are also discussed from the aspects of electrode materials, electrolyte additives and bubble management, serving as a comprehensive guide for continuous development of the water electrolysis technol.
- 2Rao, R. R.; Kolb, M. J.; Halck, N. B.; Pedersen, A. F.; Mehta, A.; You, H.; Stoerzinger, K. A.; Feng, Z.; Hansen, H. A.; Zhou, H.; Giordano, L.; Rossmeisl, J.; Vegge, T.; Chorkendorff, I.; Stephens, I. E. L.; Shao-Horn, Y. Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution. Energy Environ. Sci. 2017, 10, 2626– 2637, DOI: 10.1039/C7EE02307C2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhvVegt7bP&md5=61b7de504c9911da215e21cb94bb9505Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolutionRao, Reshma R.; Kolb, Manuel J.; Halck, Niels Bendtsen; Pedersen, Anders Filsoee; Mehta, Apurva; You, Hoydoo; Stoerzinger, Kelsey A.; Feng, Zhenxing; Hansen, Heine A.; Zhou, Hua; Giordano, Livia; Rossmeisl, Jan; Vegge, Tejs; Chorkendorff, Ib; Stephens, Ifan E. L.; Shao-Horn, YangEnergy & Environmental Science (2017), 10 (12), 2626-2637CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)While the surface at. structure of RuO2 has been well studied in ultra high vacuum, much less is known about the interaction between water and RuO2 in aq. soln. In this work, in situ surface X-ray scattering measurements combined with d. functional theory (DFT) were used to det. the surface structural changes on single-crystal RuO2(110) as a function of potential in acidic electrolyte. The redox peaks at 0.7, 1.1 and 1.4 V vs. reversible hydrogen electrode (RHE) could be attributed to surface transitions assocd. with the successive deprotonation of -H2O on the coordinatively unsatd. Ru sites (CUS) and hydrogen adsorbed to the bridging oxygen sites. At potentials relevant to the oxygen evolution reaction (OER), an -OO species on the Ru CUS sites was detected, which was stabilized by a neighboring -OH group on the Ru CUS or bridge site. Combining potential-dependent surface structures with their energetics from DFT led to a new OER pathway, where the deprotonation of the -OH group used to stabilize -OO was found to be rate-limiting.
- 3Demirbas, A. Future hydrogen economy and policy. Energy Sources, Part B 2017, 12, 172– 181, DOI: 10.1080/15567249.2014.9503943https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjs1Gis70%253D&md5=e90e9a2c5704207ac49bfe52e504b75cFuture hydrogen economy and policyDemirbas, AyhanEnergy Sources, Part B: Economics, Planning and Policy (2017), 12 (2), 172-181CODEN: ESPBAC; ISSN:1556-7249. (Taylor & Francis, Inc.)A review. Hydrogen is not a primary fuel. It must be produced from water with either fossil or renewable energy sources. Thermochem. conversion processes, such as pyrolysis, gasification, and steam gasification, are available for converting the biomass to a more useful energy. Hydrogen can be generated from carbon-neutral biomasses or carbon-free energy sources such as elec., solar, and wind energy. In this way, the use of hydrogen could eventually eliminate harmful gas emissions from the energy sector. Vehicles and stationary power generation fuelled by hydrogen are zero-emission devices at the point of use, with consequential local air-quality benefits. Hydrogen is clean and a high-energy content of fuel. Hydrogen is a peaceful energy carrier for all countries. Raw material resources of fossil fuels geog. did not distribute homogenously in the world. However, the most important source of hydrogen is water, which is almost not dependent on geog. This advantage in the development of the hydrogen economy is the most important driving force. The hydrogen economy is a vision for a future in which hydrogen replaces fossil fuels. A major dilemma now faced by the developing countries is how to invest in hydrogen research and development for the transition to hydrogen economy. The increase in the consumer sectors that energy provides is necessary for both economic and social development in the developing countries. Policy-makers will need to pay more attention to the implications for the transition to hydrogen economy.
- 4Benck, J. D.; Hellstern, T. R.; Kibsgaard, J.; Chakthranont, P.; Jaramillo, T. F. Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide Nanomaterials. ACS Catal. 2014, 4, 3957– 3971, DOI: 10.1021/cs500923c4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslahsLzJ&md5=369e7a83d320ba0b9be9f79a8db74875Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide NanomaterialsBenck, Jesse D.; Hellstern, Thomas R.; Kibsgaard, Jakob; Chakthranont, Pongkarn; Jaramillo, Thomas F.ACS Catalysis (2014), 4 (11), 3957-3971CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review. We discuss recent developments in nanostructured molybdenum sulfide catalysts for the electrochem. hydrogen evolution reaction. To develop a framework for performing consistent and meaningful comparisons between catalysts, we review std. exptl. methodologies for measuring catalyst performance and define two metrics used in this perspective for comparing catalyst activity: the turnover frequency, an intrinsic activity metric, and the total electrode activity, a device-oriented activity metric. We discuss general strategies for synthesizing catalysts with improved activity, namely, increasing the no. of elec. accessible active sites or increasing the turnover frequency of each site. Then we consider a no. of state-of-the-art molybdenum sulfide catalysts, including cryst. MoS2, amorphous MoSx, and mol. cluster materials, to highlight these strategies in practice. Comparing these catalysts reveals that most of the molybdenum sulfide catalysts have similar active site turnover frequencies, so the total electrode activity is primarily detd. by the no. of accessible active sites per geometric electrode area. Emerging strategies to overcome current catalyst limitations and potential applications for molybdenum sulfide catalysts including photoelectrochem. water splitting devices and electrolyzers are also considered.
- 5Shi, X.; Fields, M.; Park, J.; McEnaney, J. M.; Yan, H.; Zhang, Y.; Tsai, C.; Jaramillo, T. F.; Sinclair, R.; Nørskov, J. K.; Zheng, X. Rapid flame doping of Co to WS2 for efficient hydrogen evolution. Energy Environ. Sci. 2018, 11, 2270– 2277, DOI: 10.1039/C8EE01111G5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVKqsLvJ&md5=4ba0f849e4ea85776316aae4f24c78ddRapid flame doping of Co to WS2 for efficient hydrogen evolutionShi, Xinjian; Fields, Meredith; Park, Joonsuk; McEnaney, Joshua M.; Yan, Hongping; Zhang, Yirui; Tsai, Charlie; Jaramillo, Thomas F.; Sinclair, Robert; Noerskov, Jens K.; Zheng, XiaolinEnergy & Environmental Science (2018), 11 (8), 2270-2277CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)Transition metal sulfides have been widely studied as electrocatalysts for the hydrogen evolution reaction (HER). Though elemental doping is an effective way to enhance sulfide activity for the HER, most studies have only focused on the effect of doping sulfide edge sites. Few studies have investigated the effect of doping the basal plane or the effect of doping concn. on basal plane activity. Probing the dopant concn. dependence of HER activity is challenging due to exptl. difficulties in controlling dopant incorporation. Here, we overcome this challenge by first synthesizing doped transition metal oxides and then sulfurizing the oxides to sulfides, yielding core/shell Co-doped WS2/W18O49 nanotubes with a tunable amt. of Co. Our combined d. functional theory (DFT) calcns. and expts. demonstrate that the HER activity of basal plane WS2 changes non-monotonically with the concn. of Co due to local changes in the binding energy of H and the formation energy of S-vacancies. At an optimal Co doping concn., the overpotential to reach -10 mA cm-2 is reduced by 210 mV, and the Tafel slope is reduced from 122 to 49 mV per decade (mV dec-1) compared to undoped WS2 nanotubes.
- 6Lyons, M. E. G.; Doyle, R. L.; Browne, M. P.; Godwin, I. J.; Rovetta, A. A. S. Recent developments in electrochemical water oxidation. Curr. Opin. Electrochem. 2017, 1, 40– 45, DOI: 10.1016/j.coelec.2016.12.0056https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXhtVGgsL%252FO&md5=81acaad77943c99dd7e37ca020914cbeRecent developments in electrochemical water oxidationLyons, Michael E. G.; Doyle, Richard L.; Browne, Michelle P.; Godwin, Ian J.; Rovetta, Aurelie A. S.Current Opinion in Electrochemistry (2017), 1 (1), 40-45CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)A review Recent developments in electrochem. water oxidn. in aq. alk. soln. at earth abundant transition metal oxyhydroxide thin film electrodes are outlined and candidate high activity materials identified. The mol. mechanism of oxygen evolution at these oxide surfaces is discussed.
- 7Cherevko, S.; Geiger, S.; Kasian, O.; Kulyk, N.; Grote, J.-P.; Savan, A.; Shrestha, B. R.; Merzlikin, S.; Breitbach, B.; Ludwig, A.; Mayrhofer, K. J. J. Oxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stability. Catal. Today 2016, 262, 170– 180, DOI: 10.1016/j.cattod.2015.08.0147https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsVCnu7%252FE&md5=4bf7a1f1ee5806594ba98f8c86990ebeOxygen and hydrogen evolution reactions on Ru, RuO2, Ir, and IrO2 thin film electrodes in acidic and alkaline electrolytes: A comparative study on activity and stabilityCherevko, Serhiy; Geiger, Simon; Kasian, Olga; Kulyk, Nadiia; Grote, Jan-Philipp; Savan, Alan; Shrestha, Buddha Ratna; Merzlikin, Sergiy; Breitbach, Benjamin; Ludwig, Alfred; Mayrhofer, Karl J. J.Catalysis Today (2016), 262 (), 170-180CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Metallic iridium and ruthenium as well as their oxides are among the most active oxygen evolution (OER) electrocatalysts in acidic media, and are also of interest for the catalysis of the hydrogen evolution (HER). The stability of these materials under different operating conditions is, however, still not fully understood. In the current work, activity and stability of well-defined Ru, RuO2, Ir, and IrO2 thin film electrodes are evaluated in acidic and alk. electrolytes using an electrochem. scanning flow cell (SFC) connected to an inductively coupled plasma mass spectrometer (ICP-MS). Identical exptl. protocols are intentionally employed for all electrodes and electrolytes, to obtain unambiguous and comparable information on intrinsic activity and stability of the electrodes. It is found that independent of the electrolyte, OER activity decreases as Ru > Ir ≈ RuO2 > IrO2, while dissoln. increases as IrO2 « RuO2 < Ir « Ru. Moreover, dissoln. of these metals in both solns. is 2-3 orders of magnitude higher compared to their resp. oxides, and dissoln. is generally more intense in alk. solns. Similarly to the OER, metallic electrodes are more active catalysts for HER. They, however, suffer from dissoln. during native oxide redn., while IrO2 and RuO2 do not exhibit significant dissoln. The obtained results on activity and stability of the electrodes are discussed in light of their potential applications, i.e. water electrolyzers or fuel cells.
- 8Sayeed, M. A.; Herd, T.; O’Mullane, A. P. Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reaction. J. Mater. Chem. A 2016, 4, 991– 999, DOI: 10.1039/C5TA09125J8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFCksrzF&md5=359981ff1f1ea951c643f7d66003ea67Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reactionSayeed, Md Abu; Herd, Tenille; O'Mullane, Anthony P.Journal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (3), 991-999CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)The oxides of Co have recently been shown to be highly effective electrocatalysts for the O evolution reaction (OER) under alk. conditions. In general species such as Co3O4 and CoOOH were studied that often require an elevated temp. step during their synthesis to create cryst. materials. The authors study the rapid and direct electrochem. formation of amorphous nanostructured Co(OH)2 on Au electrodes under room temp. conditions which is a highly active precursor for the OER. During the OER some conversion to cryst. Co3O4 occurs at the surface, but the bulk of the material remains amorphous. The underlying Au electrode is crucial to the materials enhanced performance and provides higher c.d. than can be achieved using C, Pd or Cu support electrodes. This catalyst exhibits excellent activity with a c.d. of 10 mA cm-2 at an overpotential of 360 mV with a high turnover frequency of 2.1 s-1 in 1 M NaOH. A Tafel slope of 56 mV dec-1 at low overpotentials and a slope of 122 mV dec-1 at high overpotentials is consistent with the dual barrier model for the electrocatalytic evolution of O. Significantly, the catalyst maintains excellent activity for up to 24 h of continuous operation and this approach offers a facile way to create a highly effective and stable material.
- 9Pei, Y.; Yang, Y.; Zhang, F.; Dong, P.; Baines, R.; Ge, Y.; Chu, H.; Ajayan, P. M.; Shen, J.; Ye, M. Controlled Electrodeposition Synthesis of Co–Ni–P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water Splitting. ACS Appl. Mater. Interfaces 2017, 9, 31887– 31896, DOI: 10.1021/acsami.7b092829https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtl2lsLfO&md5=021895e827a87dcce863c4d5463297d3Controlled Electrodeposition Synthesis of Co-Ni-P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water SplittingPei, Yu; Yang, Yang; Zhang, Fangfang; Dong, Pei; Baines, Robert; Ge, Yuancai; Chu, Hang; Ajayan, Pulickel M.; Shen, Jianfeng; Ye, MingxinACS Applied Materials & Interfaces (2017), 9 (37), 31887-31896CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Synthesis of highly efficient and robust catalysts with earth-abundant resources for overall water splitting is essential for large-scale energy conversion processes. Herein, a series of highly active and inexpensive Co-Ni-P films were fabricated by a one-step const. c.d. electrodeposition method. These films were demonstrated to be efficient bifunctional catalysts for both H2 and O2 evolution reactions (HER and OER), while deposition time was deemed to be the crucial factor governing electrochem. performance. At the optimal deposition time, the obtained Co-Ni-P-2 catalyst performed remarkably for both HER and OER in alk. media. In particular, it requires -103 mV overpotential for HER and 340 mV for OER to achieve the c.d. of 10 mA cm-2, with corresponding Tafel slopes of 33 and 67 mV dec-1. Moreover, it outperforms the Pt/C//RuO2 catalyst and only needs -160 mV (430 mV) overpotential for HER (OER) to achieve 200 mA cm-2 c.d. Co-Ni-P electrodes were also conducted for the proof-of-concept exercise, which were proved to be flexible, stable, and efficient, further opening a new avenue for rapid synthesis of efficient, flexible catalysts for renewable energy resources.
- 10Escudero-Escribano, M.; Pedersen, A. F.; Paoli, E. A.; Frydendal, R.; Friebel, D.; Malacrida, P.; Rossmeisl, J.; Stephens, I. E. L.; Chorkendorff, I. Importance of Surface IrOx in Stabilizing RuO2 for Oxygen Evolution. J. Phys. Chem. B 2018, 122, 947– 955, DOI: 10.1021/acs.jpcb.7b0704710https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1yhtr3I&md5=94ceca236e222c41ee1f08e8c9f73a22Importance of Surface IrOx in Stabilizing RuO2 for Oxygen EvolutionEscudero-Escribano, Maria; Pedersen, Anders F.; Paoli, Elisa A.; Frydendal, Rasmus; Friebel, Daniel; Malacrida, Paolo; Rossmeisl, Jan; Stephens, Ifan E. L.; Chorkendorff, IbJournal of Physical Chemistry B (2018), 122 (2), 947-955CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)The high precious metal loading and high overpotential of the oxygen evolution reaction (OER) prevents the widespread use of polymer electrolyte membrane (PEM) water electrolyzers. Herein the authors explore the OER activity and stability in acidic electrolyte of a combined IrOx/RuO2 system consisting of RuO2 thin films with submonolayer (1, 2, and 4 Å) amts. of IrOx deposited on top. Operando extended x-ray absorption fine structure (EXAFS) on the Ir L-3 edge revealed a rutile type IrO2 structure with some Ir sites occupied by Ru, IrOx being at the surface of the RuO2 thin film. The authors monitor corrosion on IrOx/RuO2 thin films by combining electrochem. quartz crystal microbalance (EQCM) with inductively coupled mass spectrometry (ICP-MS). The authors elucidate the importance of submonolayer surface IrOx in minimizing Ru dissoln. The authors can tune the surface properties of active OER catalysts, such as RuO2, aiming to achieve higher electrocatalytic stability in PEM electrolyzers.
- 11Browne, M. P.; O’Rourke, C.; Mills, A. A mechanical, high surface area and solvent-free ‘powder-to-electrode’ fabrication method for screening OER catalysts. Electrochem. Commun. 2017, 85, 1– 5, DOI: 10.1016/j.elecom.2017.10.01111https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs12rsbvJ&md5=3e98b9f2cf64f9ca09f0f58885faa045A mechanical, high surface area and solvent-free 'powder-to-electrode' fabrication method for screening OER catalystsBrowne, M. P.; O'Rourke, C.; Mills, A.Electrochemistry Communications (2017), 85 (), 1-5CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)The screening of new OER materials routinely involves fabricating electrodes from powders using methods which are often time consuming and may involve using solvents and/or conductive materials that can alter the OER activity of the powder. Herein, a new mech., solvent-free method for fabricating electrodes for OER is described in which a electroactive material under test, mixed with a small amt. of PTFE powder (ca. 10 wt%), is pressed onto Pt powder to create a permanent, robust electrode that can be used in a rotating disc electrode set-up. This new method of fabricating electrodes is compared to the well-known dropcast on Glassy Carbon (GC) method, using com. available materials: RuO2, Co3O4 and NiO. The results show that the mech. route produces much better OER performances, in terms of overpotential and stability, for the com. metal oxide on the pressed disks when compared to the dropcast GC method. Finally, it is shown that this mech., high surface area, solvent-free electrode fabrication technique can also be achieved using silver, rather than platinum, as the conducting, support material.
- 12Stoerzinger, K. A.; Qiao, L.; Biegalski, M. D.; Shao-Horn, Y. Orientation-Dependent Oxygen Evolution Activities of Rutile IrO2 and RuO2. J. Phys. Chem. Lett. 2014, 5, 1636– 1641, DOI: 10.1021/jz500610u12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXms1Wiu7o%253D&md5=d40da2689df2faa48ad9dea72b21e7d6Orientation-Dependent Oxygen Evolution Activities of Rutile IrO2 and RuO2Stoerzinger, Kelsey A.; Qiao, Liang; Biegalski, Michael D.; Yang, Shao-HornJournal of Physical Chemistry Letters (2014), 5 (10), 1636-1641CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The activities of the O evolution reaction (OER) on IrO2 and RuO2 catalysts are among the highest known to date. However, the intrinsic OER activities of surfaces with defined crystallog. orientations are not well-established exptl. Here the authors report that the (100) surface of IrO2 and RuO2 is more active in alk. environments (pH 13) than the most thermodynamically stable (110) surface. The OER activity was correlated with the d. of coordinatively undersatd. metal sites of each crystallog. facet. The surface-orientation-dependent activities can guide the design of nanoscale catalysts with increased activity for electrolyzers, metal-air batteries, and photoelectrochem. H2O splitting applications.
- 13Gao, X.; Zhang, H.; Li, Q.; Yu, X.; Hong, Z.; Zhang, X.; Liang, C.; Lin, Z. Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water-Splitting. Angew. Chem., Int. Ed. 2016, 55, 6290– 6294, DOI: 10.1002/anie.20160052513https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvVagtL0%253D&md5=f5b3ef8828f660655706b7230daff9bfHierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water-SplittingGao, Xuehui; Zhang, Hongxiu; Li, Quanguo; Yu, Xuegong; Hong, Zhanglian; Zhang, Xingwang; Liang, Chengdu; Lin, ZhanAngewandte Chemie, International Edition (2016), 55 (21), 6290-6294CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alk. electrolyte may improve the efficiency of overall water splitting. Nickel cobaltite (NiCo2O4) has been considered a promising electrode material for the OER. However, NiCo2O4 that can be used as an electrocatalyst in HER has not been studied yet. Herein, we report self-assembled hierarchical NiCo2O4 hollow microcuboids for overall water splitting including both the HER and OER reactions. The NiCo2O4 electrode shows excellent activity toward overall water splitting, with 10 mA/cm2 water-splitting current reached by applying just 1.65 V and 20 mA/cm2 by applying just 1.74 V across the two electrodes. The synthesis of NiCo2O4 microflowers confirms the importance of structural features for high-performance overall water splitting.
- 14Etzi Coller Pascuzzi, M.; Goryachev, A.; Hofmann, J. P.; Hensen, E. J. M. Mn promotion of rutile TiO2-RuO2 anodes for water oxidation in acidic media. Appl. Catal., B 2020, 261, 118225 DOI: 10.1016/j.apcatb.2019.11822514https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFWisLfN&md5=78d8e8cb9ccfa1096c2e55b65e27c5bfMn promotion of rutile TiO2-RuO2 anodes for water oxidation in acidic mediaEtzi Coller Pascuzzi, Marco; Goryachev, Andrey; Hofmann, Jan P.; Hensen, Emiel J. M.Applied Catalysis, B: Environmental (2020), 261 (), 118225CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)A method to reduce noble metal content in oxygen-evolving electrocatalysts suitable to work in acidic media is presented. TiO2-RuO2 anodes can be promoted by Mn, resulting in increased activity and stability. The most active compn. displayed an overpotential of 386 mV at a c.d. of 10 mA cm-2, and a Tafel slope of 50 mV dec-1. This anode only included 17 at% Ru out of the total amt. of metals included in the film. We investigated the influence of Mn addn. to TiO2-RuO2 on the structure, morphol., and surface area, and related differences to catalytic activity and stability. We found that increased porosity of the anode film by Mn addn. and Mn inclusion in the TiO2-RuO2 lattice can explain the enhanced catalytic activity. A detailed characterization of fresh and used anodes provided insight into structural modifications induced by electrochem. treatment.
- 15Browne, M. P.; Nolan, H.; Duesberg, G. S.; Colavita, P. E.; Lyons, M. E. G. Low-Overpotential High-Activity Mixed Manganese and Ruthenium Oxide Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media. ACS Catal. 2016, 6, 2408– 2415, DOI: 10.1021/acscatal.5b0206915https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjsFaqu7g%253D&md5=13dc3e0b2e3172da1c795162d00e5c53Low-Overpotential High-Activity Mixed Manganese and Ruthenium Oxide Electrocatalysts for Oxygen Evolution Reaction in Alkaline MediaBrowne, Michelle P.; Nolan, Hugo; Duesberg, Georg S.; Colavita, Paula E.; Lyons, Michael E. G.ACS Catalysis (2016), 6 (4), 2408-2415CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Mixed Mn/Ru oxide thermally prepd. electrodes using different compns. of Mn and Ru precursor salts have been fabricated on Ti supports via thermal decompn. at two annealing temps. Subsequently, the oxygen evolution reaction (OER) activities of these electrodes were detd. A majority of the mixed Mn/Ru catalysts are highly active for the OER, exhibiting lower overpotential values compared to those of the state-of-the-art RuO2 and IrO2 type materials, when measured at a c.d. of 10 mA cm-2. These Mn/Ru oxide materials are also cheaper to produce than the aforementioned platinum group materials, therefore rendering the Mn/Ru materials more practical and economical. The Mn/Ru catalysts are also evaluated with respect to their Tafel slopes and turnover frequency nos. Interestingly, SEM reveals that the morphologies of the electrodes change to a mud-cracked morphol., similar to that of the RuO2, with minimal amts. of the Ru precursor salt added to the Mn salt. Fourier transform IR spectroscopy and X-ray diffraction show that the Mn material fabricated in this study at the two annealing temps. is largely Mn3O4, while the Ru material is predominately RuO2. XPS was also used to investigate the Mn and Ru compn. ratios in each of the films.
- 16Browne, M. P.; Nolan, H.; Twamley, B.; Duesberg, G. S.; Colavita, P. E.; Lyons, M. E. G. Thermally Prepared Mn2O3/RuO2/Ru Thin Films as Highly Active Catalysts for the Oxygen Evolution Reaction in Alkaline Media. ChemElectroChem 2016, 3, 1847– 1855, DOI: 10.1002/celc.20160037016https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhtlalsLrK&md5=1dbd1790c02f97209a994920449c5066Thermally prepared Mn2O3 /RuO2/Ru thin films as highly active catalysts for the Oxygen Evolution Reaction in Alkaline MediaBrowne, Michelle; Nolan, Hugo; Twamley, Brendan; Duesberg, Georg; Colavita, Paula; Lyons, MichaelChemElectroChem (2016), 3 (11), 1847-1855CODEN: CHEMRA; ISSN:2196-0216. (Wiley-VCH Verlag GmbH & Co. KGaA)Herein, a thermal decompn. method was utilized to fabricate pure and mixed manganese and ruthenium oxides for catalysts in the Oxygen Evolution Reaction (OER). XPS and X-ray Diffraction (XRD) reveal the manganese and ruthenium species produced at the annealing temp. of 600 C to be Mn2O3 and RuO2/Ru, resp. A no. of the mixed Mn/Ru oxides exhibit overpotential values, at a c.d. of 10 mA cm-2, approx. 200 mV lower than previously reported for Mn2O3/RuO2 oxides for the OER, while the Mn 50 material exhibits similar overpotentials reported by RuO2. Turnover Frequency (TOF) nos. for the Mn/Ru oxides were also calcd. and the results show that the TOF values for some of these materials are higher than RuO2. XPS anal. indicates a change in chem. environment of the Mn/Ru materials which exhibit higher TOF values. Subsequently, the pure Ru 100 material, in this study, has a lower overpotential at 10mA cm-2, when compared to previously reported values in the literature for RuO2 in alk. media. This may be due to the presence of metallic Ru found in the film or the decrease in crystallite size, detd. by XRD. XPS anal. was also carried out after OER to help det. the order of activity for the materials in this work.
- 17Wu, Y.; Tariq, M.; Zaman, W. Q.; Sun, W.; Zhou, Z.; Yang, J. Bimetallic Doped RuO2 with Manganese and Iron as Electrocatalysts for Favorable Oxygen Evolution Reaction Performance. ACS Omega 2020, 5, 7342– 7347, DOI: 10.1021/acsomega.9b0423717https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXlsVeqsrc%253D&md5=a33705b2555b4d9054938a039895e32fBimetallic Doped RuO2 with Manganese and Iron as Electrocatalysts for Favorable Oxygen Evolution Reaction PerformanceWu, Yiyi; Tariq, Muhammad; Zaman, Waqas Qamar; Sun, Wei; Zhou, Zhenhua; Yang, JiACS Omega (2020), 5 (13), 7342-7347CODEN: ACSODF; ISSN:2470-1343. (American Chemical Society)Synthesizing oxygen evolution reaction (OER) catalysts with enhanced activity by codoping has been proven to be a feasible approach for the efficient use of noble metals via renewing their basic intrinsic properties. In continuation of the research in codoping, we prep. a ruthenium-based bimetallic doped catalyst MnxFeyRu1-x-yO2 with an outstanding OER activity as compared to pure RuO2, one of the state-of-the-art OER catalysts. The synthesized codoped RuO2 with a Mn/Fe molar ratio of 1 reflected a Tafel slope of only 41 mV dec-1, which is appreciably lower than 64 mV dec-1 for pure RuO2. The XPS performed reveals that oxygen vacancy and manganese valency are the key factors of the OER activity for codoped catalysts.
- 18Lin, C.; Li, J.-L.; Li, X.; Yang, S.; Luo, W.; Zhang, Y.; Kim, S.-H.; Kim, D.-H.; Shinde, S. S.; Li, Y.-F.; Liu, Z.-P.; Jiang, Z.; Lee, J.-H. In-situ reconstructed Ru atom array on α-MnO2 with enhanced performance for acidic water oxidation. Nat. Catal. 2021, 4, 1012– 1023, DOI: 10.1038/s41929-021-00703-018https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXislOltLbI&md5=fa482c87b1e994cc9f16c1955be6023aIn-situ reconstructed Ru atom array on α-MnO2 with enhanced performance for acidic water oxidationLin, Chao; Li, Ji-Li; Li, Xiaopeng; Yang, Shuai; Luo, Wei; Zhang, Yaojia; Kim, Sung-Hae; Kim, Dong-Hyung; Shinde, Sambhaji S.; Li, Ye-Fei; Liu, Zhi-Pan; Jiang, Zheng; Lee, Jung-HoNature Catalysis (2021), 4 (12), 1012-1023CODEN: NCAACP; ISSN:2520-1158. (Nature Portfolio)The development of acid-stable oxygen evolution reaction electrocatalysts is essential for high-performance water splitting. Here, we report an electrocatalyst with Ru-atom-array patches supported on α-MnO2 (Ru/MnO2) for the oxygen evolution reaction following a mechanism that involves only *O and *OH species as intermediates. This mechanism allows direct O-O radical coupling for O2 evolution. Ru/MnO2 shows high activity (161 mV at 10 mA cm-2) and outstanding stability with small degrdn. after 200 h operation, making it one of the best-performing acid-stable oxygen evolution reaction catalysts. Operando vibrational and mass spectroscopy measurements were performed to probe the reaction intermediates and gaseous products for validating the oxygen evolution reaction pathway. First-principles calcns. confirmed the cooperative catalysis mechanism with a reduced energy barrier. Time-dependent elemental anal. demonstrated the occurrence of the in-situ dynamic cation exchange reaction during the oxygen evolution reaction, which is the key for triggering the reconstruction of Ru atoms into the ordered array with high durability.
- 19Gorlin, Y.; Lassalle-Kaiser, B.; Benck, J. D.; Gul, S.; Webb, S. M.; Yachandra, V. K.; Yano, J.; Jaramillo, T. F. In situ X-ray absorption spectroscopy investigation of a bifunctional manganese oxide catalyst with high activity for electrochemical water oxidation and oxygen reduction. J. Am. Chem. Soc. 2013, 135, 8525– 8534, DOI: 10.1021/ja310463219https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXoslSqt74%253D&md5=65ec2e82e2a005e5b1985e30baf47054In Situ X-ray Absorption Spectroscopy Investigation of a Bifunctional Manganese Oxide Catalyst with High Activity for Electrochemical Water Oxidation and Oxygen ReductionGorlin, Yelena; Lassalle-Kaiser, Benedikt; Benck, Jesse D.; Gul, Sheraz; Webb, Samuel M.; Yachandra, Vittal K.; Yano, Junko; Jaramillo, Thomas F.Journal of the American Chemical Society (2013), 135 (23), 8525-8534CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)In situ x-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochem. systems, with the ability to elucidate the chem. nature of electrocatalysts under reaction conditions. The authors perform in situ XAS measurements on a bifunctional Mn oxide (MnOx) catalyst with high electrochem. activity for the O redn. reaction (ORR) and the O evolution reaction (OER). Using x-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), exposure to an ORR-relevant potential of 0.7 V vs. RHE produces a disordered MnII3,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs. RHE, relevant to the OER, the authors observe an oxidn. of ∼80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged MnII3,III,IIIO4. XAS and electrochem. characterization of two thin film catalysts with different MnOx thicknesses reveals no significant influence of thickness on the measured oxidn. states, at either ORR or OER potentials, but demonstrates that the OER activity scales with film thickness. Probably the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film. As the portion of the catalyst film that is most likely to be oxidized at the high potentials necessary for the OER is that which is closest to the electrolyte interface, the authors hypothesize that the MnIII,IV oxide, rather than MnII3,III,IIIO4, is the phase pertinent to the obsd. OER activity.
- 20Frydendal, R.; Seitz, L. C.; Sokaras, D.; Weng, T.-C.; Nordlund, D.; Chorkendorff, I.; Stephens, I. E. L.; Jaramillo, T. F. Operando investigation of Au-MnOx thin films with improved activity for the oxygen evolution reaction. Electrochim. Acta 2017, 230, 22– 28, DOI: 10.1016/j.electacta.2017.01.08520https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjsVKnsbo%253D&md5=eab2e28132f27c7ad3c06783d8d9b220Operando investigation of Au-MnOx thin films with improved activity for the oxygen evolution reactionFrydendal, Rasmus; Seitz, Linsey C.; Sokaras, Dimosthenis; Weng, Tsu-Chien; Nordlund, Dennis; Chorkendorff, Ib; Stephens, Ifan E. L.; Jaramillo, Thomas F.Electrochimica Acta (2017), 230 (), 22-28CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)The electrochem. splitting of water holds great potential as a method for producing clean fuels by storing electricity from intermittent energy sources. The efficiency of such a process would be greatly facilitated by incorporating more active catalysts based on abundant materials for the oxygen evolution reaction. Manganese oxides are promising as catalysts for this reaction. Recent reports show that their activity can be drastically enhanced when modified with gold. Herein, we investigate highly active mixed Au-MnOx thin films for the oxygen evolution reaction, which exhibit more than five times improvement over pure MnOx. These films are characterized with operando X-ray Absorption Spectroscopy, which reveal that Mn assumes a higher oxidn. state under reaction conditions when Au is present. The magnitude of the enhancement is correlated to the size of the Au domains, where larger domains are the more beneficial.
- 21Lian, S.; Browne, M. P.; Domínguez, C.; Stamatin, S. N.; Nolan, H.; Duesberg, G. S.; Lyons, M. E. G.; Fonda, E.; Colavita, P. E. Template-free synthesis of mesoporous manganese oxides with catalytic activity in the oxygen evolution reaction. Sustainable Energy Fuels 2017, 1, 780– 788, DOI: 10.1039/C7SE00086C21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1Crs7bM&md5=31fa10223e399a8a6a4e3247c0e250f8Template-free synthesis of mesoporous manganese oxides with catalytic activity in the oxygen evolution reactionLian, Suoyuan; Browne, Michelle P.; Dominguez, Carlota; Stamatin, Serban N.; Nolan, Hugo; Duesberg, Georg S.; Lyons, Michael E. G.; Fonda, Emiliano; Colavita, Paula E.Sustainable Energy & Fuels (2017), 1 (4), 780-788CODEN: SEFUA7; ISSN:2398-4902. (Royal Society of Chemistry)Porous manganese carbonate was obtained via solvothermal synthesis using ethanol and urea. The manganese carbonate was subsequently used as a precursor to synthesize mesoporous manganese oxides via thermal treatments at three various temps. X-ray diffraction and Extended X-ray Absorption Fine Structure (EXAFS) results shows that γ-MnO2 is synthesized at 380 and 450°C while Mn2O3 is produced at the annealing temp. of 575°C. X-ray absorption spectra show that γ-MnO2 converts completely to Mn2O3 after annealing over the 450-575°C range. The oxides obtained at 380°C and 450°C possess extremely high sp. surface area, which is of interest for catalytic applications. The oxides were investigated as electrocatalysts for the oxygen evolution reaction; the oxide prepd. at the lowest annealing temp. was found to be the optimum catalyst with an overpotential of 427 ± 10 mV at a c.d. of 10 mA cm-2, normalized by the geometric area. The improved catalytic activity was related to the presence of defect-rich and highly porous manganese dioxide at the lowest annealing temp.
- 22Petrykin, V.; Bastl, Z.; Franc, J.; Macounova, K.; Makarova, M.; Mukerjee, S.; Ramaswamy, N.; Spirovova, I.; Krtil, P. Local Structure of Nanocrystalline Ru1–xNixO2–δ Dioxide and Its Implications for Electrocatalytic Behavior─An XPS and XAS Study. J. Phys. Chem. C 2009, 113, 21657– 21666, DOI: 10.1021/jp904935e22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhsFSrsb3K&md5=d0c70fefe8e7ff11c0fc971919412b11Local Structure of Nanocrystalline Ru1-xNixO2-δ Dioxide and Its Implications for Electrocatalytic Behavior - An XPS and XAS StudyPetrykin, V.; Bastl, Z.; Franc, J.; Macounova, K.; Makarova, M.; Mukerjee, S.; Ramaswamy, N.; Spirovova, I.; Krtil, P.Journal of Physical Chemistry C (2009), 113 (52), 21657-21666CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Chem. compn., crystal structure, as well as short-range at. arrangement of nanocryst. Ru1-xNixO2-δ (x = 0.05, 0.1, 0.15, 0.2, 0.3) were studied using energy dispersive x-ray spectroscopy (EDX), XPS, and X-ray absorption spectroscopy (XAS). The prepd. materials form single-phase nanocrystals with rutile structure. Regardless of the chem. compn., the surface of Ru1-xNixO2-δ oxides is Ni-enriched with respect to overall chem. compn. According to both XPS and XANES, the oxidn. state of Ru remains +4 in the studied materials. Ni ions are present in both divalent and trivalent states with the fraction of trivalent ions decreasing with increasing Ni content. The refinement of local structure using EXAFS data based on Ru-K and Ni-K edge absorption spectra shows that Ru preserves local arrangement characteristic for Ru dioxide. The incorporated Ni shows a tendency to form clusters within a rutile structure for low Ni concn. At high Ni content, the architecture of the Ni-rich defects resembles architecture of shear planes in oxygen -deficient rutile. These Ni-rich regions likely manifest themselves on the surface as line or plane defects, which are the most likely structural features active in the electrocatalytic processes in oxygen and chlorine evolution.
- 23Seitz, L. C.; Nordlund, D.; Gallo, A.; Jaramillo, T. F. Tuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution Reaction. Electrochim. Acta 2016, 193, 240– 245, DOI: 10.1016/j.electacta.2016.01.20023https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XivVCktbk%253D&md5=c981aa03865018ca6cf6068316ea2affTuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution ReactionSeitz, Linsey C.; Nordlund, Dennis; Gallo, Alessandro; Jaramillo, Thomas F.Electrochimica Acta (2016), 193 (), 240-245CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)Understanding catalyst function to improve activity for the O evolution reaction (OER) is key to increasing the overall efficiency of electrochem. H2O splitting, a promising method for sustainable and clean prodn. of H. Using a straightforward and scalable sol-gel synthesis, the authors explore the effects of metal compn. in CoxTi1-xOy on electrochem. activity, at. structure, and electronic state. Phys. and electronic characterization reveal that increased amts. of Ti stabilize the 2+ oxidn. state of the Co precursor and give less active CoO-like catalysts. Conversely, films with Co:Ti ratios of 1:1 or greater result in catalysts with high activity, correlating with greater Co 3+ character, as measured by ex situ XAS for samples as-prepd. and after exposure to OER conditions. Addnl., decreasing the Ti content systematically shifts the Co redox potential from ∼1.5 V vs. RHE with a 1:3 Co:Ti ratio to 1.0 V vs. RHE with no Ti, further evidence that Ti stabilizes Co in a lower oxidn. state. Controlling the oxidn. state of metals in metal-oxide OER catalysts can have a profound effect on catalytic activity.
- 24Abbott, D. F.; Lebedev, D.; Waltar, K.; Povia, M.; Nachtegaal, M.; Fabbri, E.; Copéret, C.; Schmidt, T. J. Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from Operando XAS. Chem. Mater. 2016, 28, 6591– 6604, DOI: 10.1021/acs.chemmater.6b0262524https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVeht7jM&md5=45b8a8fb48922d66af500be4bf9d2b59Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from Operando XASAbbott, Daniel F.; Lebedev, Dmitry; Waltar, Kay; Povia, Mauro; Nachtegaal, Maarten; Fabbri, Emiliana; Coperet, Christophe; Schmidt, Thomas J.Chemistry of Materials (2016), 28 (18), 6591-6604CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)A current challenge faced in H2O electrolysis is the development of structure-activity relations for understanding and improving IrOx-based catalysts for the O evolution reaction (OER). The authors report a simple and scalable modified Adams fusion method for prepg. highly OER active, Cl-free Ir oxide nanoparticles of various size and shape. The applied approach allows for the effects of particle size, morphol., and the nature of the surface species on the OER activity of IrO2 to be studied. Ir oxide synthesized at 350° from Ir(acac)3, consisting of 1.7 ± 0.4 nm particles with a sp. surface area of 150 m2 g-1, shows the highest OER activity (E = 1.499 ± 0.003 V at 10 A gox-1). Operando x-ray absorption spectroscopy (XAS) and XPS studies indicate Ir hydroxo (Ir-OH) surface species, which are strongly linked to the OER activity. Prepn. of larger IrO2 particles using higher temps. results in a change of the particle morphol. from spherical to rod-shaped particles. A decrease of the intrinsic OER activity was assocd. with the predominant termination of the rod-shape particles by highly ordered (110) facets in addn. to limited diffusion within mesoporous features.
- 25Gorlin, Y.; Chung, C.-J.; Benck, J. D.; Nordlund, D.; Seitz, L.; Weng, T.-C.; Sokaras, D.; Clemens, B. M.; Jaramillo, T. F. Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation. J. Am. Chem. Soc. 2014, 136, 4920– 4926, DOI: 10.1021/ja407581w25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXkslalt7w%253D&md5=75bb3f8adb37fbebda812e48a79e4cd0Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water OxidationGorlin, Yelena; Chung, Chia-Jung; Benck, Jesse D.; Nordlund, Dennis; Seitz, Linsey; Weng, Tsu-Chien; Sokaras, Dimosthenis; Clemens, Bruce M.; Jaramillo, Thomas F.Journal of the American Chemical Society (2014), 136 (13), 4920-4926CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnO, a promising OER catalyst. We conclusively demonstrate that adding Au to MnO significantly enhances OER activity relative to MnO in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnO catalysts reported to date. We also provide evidence that it is a local rather than bulk interaction between Au and MnO that leads to the obsd. enhancement in the OER activity. Engineering improvements in nonprecious metal-based catalysts by the addn. of Au or other noble metals could still represent a scalable catalyst as even trace amts. of Au are shown to lead a significant enhancement in the OER activity of MnO.
- 26Petrykin, V.; Macounová, K.; Okube, M.; Mukerjee, S.; Krtil, P. Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolution. Catal. Today 2013, 202, 63– 69, DOI: 10.1016/j.cattod.2012.03.07526https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XntVyrurw%253D&md5=b84968444c0e8740adb917cbb50e6005Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolutionPetrykin, Valery; Macounova, Katerina; Okube, Maki; Mukerjee, Sanjeev; Krtil, PetrCatalysis Today (2013), 202 (), 63-69CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)Nano-particulate Co doped ruthenium dioxide electrocatalysts of the general formula Ru1-xCoxO2-y (0 < x 0.3) were prepd. by a co-pptn. method. The electrocatalysts with x < 0.2 conform to a single phase nano-cryst. materials. On the local level the Co forms clusters dispersed in the original rutile-like matrix. The local environment of the Co conforms to a rutile model which preserves the cationic arrangement but suppresses the probability of the Ru-Ru and Co-Co neighbors along the shortest metal-metal bonds. The electrocatalytic activity of the synthesized Ru1-xCoxO2-y materials in oxygen evolution is comparable with that of the non-doped ruthenium dioxide and little depends on the actual Co content. In presence of chlorides the Co doped materials are more selective towards oxygen evolution compared with the non doped ruthenia. The enhanced oxygen evolution in the case of Co doped electrocatalysts can be attributed to a chem. recombination of surface confined oxo-species. The selectivity shift towards oxygen evolution can be linked with limited activity of the Ru1-xCoxO2-y materials in the chlorine evolution reaction which seems to be relatively weakly dependent on the chloride concn.
- 27Petrykin, V.; Macounova, K.; Shlyakhtin, O. A.; Krtil, P. Tailoring the Selectivity for Electrocatalytic Oxygen Evolution on Ruthenium Oxides by Zinc Substitution. Angew. Chem., Int. Ed. 2010, 49, 4813– 4815, DOI: 10.1002/anie.20090712827https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXotVCgu7w%253D&md5=ac55be8552da19210ab83b7d01d96d70Tailoring the selectivity for electrocatalytic oxygen evolution on ruthenium oxides by zinc substitutionPetrykin, V.; Macounova, K.; Shlyakhtin, O. A.; Krtil, PetrAngewandte Chemie, International Edition (2010), 49 (28), 4813-4815, S4813/1-S4813/3CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)The voltammetry results combined with differential electrochem. mass spectroscopy (DEMS) data show significant selectivity of the Ru-Zn-O oxides towards the oxygen-evolution reactions even in chloride-contg. systems.
- 28Biesinger, M. C.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn. Appl. Surf. Sci. 2010, 257, 887– 898, DOI: 10.1016/j.apsusc.2010.07.08628https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtFOqsbrM&md5=b1ded0992b488ad83c6195c17c9ba4b9Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and ZnBiesinger, Mark C.; Lau, Leo W. M.; Gerson, Andrea R.; Smart, Roger St. C.Applied Surface Science (2010), 257 (3), 887-898CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)Chem. state x-ray photoelectron spectroscopic anal. of 1st row transition metals and their oxides and hydroxides is challenging due to the complexity of the 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. Current literature shows that all values necessary for reproducible, quant. chem. state anal. are usually not provided. A more consistent, practical and effective approach to curve-fitting the various chem. states in a variety of Sc, Ti, V, Cu and Zn metals, oxides and hydroxides is reported. The curve-fitting procedures proposed are based on a combination of (1) std. spectra from quality ref. samples, (2) a survey of appropriate literature databases and/or a compilation of the literature refs., and (3) specific literature refs. where fitting procedures are available. Binding energies, full-width at half max. (FWHM) values, spin-orbit splitting values, asym. peak-shape fitting parameters, and, for Cu and Zn, Auger parameters values are presented. The quantification procedure for Cu species details the use of the shake-up satellites for Cu(II)-contg. compds. and the exact binding energies of the Cu(0) and Cu(I) peaks. The use of the modified Auger parameter for Cu and Zn species allows for corroborating evidence when there is uncertainty in the binding energy assignment. These procedures can remove uncertainties in anal. of surface states in nano-particles, corrosion, catalysis and surface-engineered materials.
- 29Newville, M. EXAFS analysis using FEFF and FEFFIT. J. Synchrotron Radiat. 2001, 8, 96– 100, DOI: 10.1107/S090904950001629029https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhs1amt7s%253D&md5=97e5f5081ebd6f0313b8462da7f7231bEXAFS analysis using FEFF and FEFFITNewville, MatthewJournal of Synchrotron Radiation (2001), 8 (2), 96-100CODEN: JSYRES; ISSN:0909-0495. (Munksgaard International Publishers Ltd.)Some of the advanced EXAFS anal. features of FEFF and FEFFIT are described. The scattering path formalism from FEFF and cumulant expansion are used as the basic building blocks of EXAFS anal., giving a flexible and robust parameterization of most EXAFS problems. The ability to model EXAFS data in terms of generalized phys. variables is shown, including the simultaneous refinement of 2 different polarizations for Co K EXAFS data of CoPt3.
- 30Newville, M. IFEFFIT: interactive XAFS analysis and FEFF fitting. J. Synchrotron Radiat. 2001, 8, 322– 324, DOI: 10.1107/S090904950001696430https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXhs1als7c%253D&md5=38aec52f539e7522f80468400f90cef1IFEFFIT: interactive XAFS analysis and FEFF fittingNewville, MatthewJournal of Synchrotron Radiation (2001), 8 (2), 322-324CODEN: JSYRES; ISSN:0909-0495. (Munksgaard International Publishers Ltd.)IFEFFIT, an interactive program and scriptable library of XAFS algorithms is presented. The core algorithms of AUTOBK and FEFFIT were combined with general data manipulation and interactive graphics into a single package. IFEFFIT comes with a command-line program that can be run either interactively or in batch-mode. It also provides a library of functions that can be used easily from C or Fortran, as well as high level scripting languages such as Tcl, Perl and Python. Using this library, a Graphical User Interface for rapid 'online' data anal. is demonstrated. IFEFFIT is freely available with an Open Source license. Outside use, development, and contributions are encouraged.
- 31Diebold, U.; Madey, T. E. TiO2 by XPS. Surf. Sci. Spectra 1996, 4, 227– 231, DOI: 10.1116/1.1247794There is no corresponding record for this reference.
- 32Di Castro, V.; Polzonetti, G. XPS study of MnO oxidation. J. Electron Spectrosc. Relat. Phenom. 1989, 48, 117– 123, DOI: 10.1016/0368-2048(89)80009-X32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL1MXit1Cgsbg%253D&md5=f0e15920bae10142febdcd1bb0411f9fXPS study of manganese monoxide oxidationDi Castro, V.; Polzonetti, G.Journal of Electron Spectroscopy and Related Phenomena (1989), 48 (1-2), 117-23CODEN: JESRAW; ISSN:0368-2048.The oxidn. of a MnO layer was studied by XPS at 400°. Pure Mn oxides were measured for comparison and the Mn oxidn. states were identified by Mn2p binding energy, Mn2p satellite structure, Mn3s multiplet splitting and valence spectra. A progressive oxidn. of MnO to Mn2O3 without intermediate formation of Mn3O4 was obsd. Comparison of core and valence spectra indicates that a thin layer of Mn2O3 is initially formed on top of MnO. At higher O2 exposure the MnO is completely oxidized to Mn2O3.
- 33Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S. C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717– 2730, DOI: 10.1016/j.apsusc.2010.10.05133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXjtVWntw%253D%253D&md5=dcecf58a93c37118aa69743501f10816Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and NiBiesinger, Mark C.; Payne, Brad P.; Grosvenor, Andrew P.; Lau, Leo W. M.; Gerson, Andrea R.; Smart, Roger St. C.Applied Surface Science (2011), 257 (7), 2717-2730CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)Chem. state x-ray photoelectron spectroscopic anal. of 1st row transition metals and their oxides and hydroxides is challenging due to the complexity of their 2p spectra resulting from peak asymmetries, complex multiplet splitting, shake-up and plasmon loss structure, and uncertain, overlapping binding energies. The previous paper in which the authors examd. Sc, Ti, V, Cu and Zn species, showed that all the values of the spectral fitting parameters for each specific species, i.e. binding energy (eV), full wide at half max. (FWHM) value (eV) for each pass energy, spin-orbit splitting values and asym. peak shape fitting parameters, are not all normally provided in the literature and data bases, and are necessary for reproducible, quant. chem. state anal. A more consistent, practical and effective approach to curve fitting was developed based on a combination of (1) std. spectra from quality ref. samples, (2) a survey of appropriate literature databases and/or a compilation of literature refs. and (3) specific literature refs. where fitting procedures are available. This paper extends this approach to the chem. states of Cr, Mn, Fe, Co and Ni metals, and various oxides and hydroxides where intense, complex multiplet splitting in many of the chem. states of these elements poses unique difficulties for chem. state anal. The curve fitting procedures proposed use the same criteria as proposed previously but with the addnl. complexity of fitting of multiplet split spectra which was done based on spectra of numerous ref. materials and theor. XPS modeling of these transition metal species. Binding energies, FWHM values, asym. peak shape fitting parameters, multiplet peak sepn. and peak area percentages are presented. The procedures developed can be used to remove uncertainties in the anal. of surface states in nanoparticles, corrosion, catalysis and surface-engineered materials.
- 34Wöllner, A.; Lange, F.; Schmelz, H.; Knözinger, H. Characterization of mixed copper-manganese oxides supported on titania catalysts for selective oxidation of ammonia. Appl. Catal., A 1993, 94, 181– 203, DOI: 10.1016/0926-860X(93)85007-CThere is no corresponding record for this reference.
- 35Wei, Y. J.; Yan, L. Y.; Wang, C. Z.; Xu, X. G.; Wu, F.; Chen, G. Effects of Ni Doping on [MnO6] Octahedron in LiMn2O4. J. Phys. Chem. B 2004, 108, 18547– 18551, DOI: 10.1021/jp047952235https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXpt1Cqsbw%253D&md5=95352c741c029f57b6037a8b035c21f9Effects of Ni Doping on [MnO6] Octahedron in LiMn2O4Wei, Y. J.; Yan, L. Y.; Wang, C. Z.; Xu, X. G.; Wu, F.; Chen, G.Journal of Physical Chemistry B (2004), 108 (48), 18547-18551CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)LiNixMn2-xO4 (x ≤ 0.5) powders were synthesized using a sol-gel technique. Partial Ni atoms occupy the 8a sites in heavy doped LiNixMn2-xO4 via x-ray diffraction. XPS results showed an increase and a decrease in the av. valence state of Mn and Ni ions, resp., with the nickel content. Five Raman modes of LiNixMn2-xO4 were obsd. The A1g band was obsd. being shifted to higher frequency for x ≤ 0.2 and shifted to lower frequency for x > 0.2. The most rigid [MnO6] octahedron occurs at x = 0.2. [MnO6] octahedron in LiNi0.2Mn1.8O4 possesses the strongest rigidity with respect to the other LiNixMn2-xO4 (x < 0.5 and ≠ 0.2).
- 36Morgan, D. J. Resolving ruthenium: XPS studies of common ruthenium materials. Surf. Interface Anal. 2015, 47, 1072– 1079, DOI: 10.1002/sia.585236https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhsFehsr7J&md5=719e072bfc36ab8bc6c09d7f09240285Resolving ruthenium: XPS studies of common ruthenium materialsMorgan, David J.Surface and Interface Analysis (2015), 47 (11), 1072-1079CODEN: SIANDQ; ISSN:0142-2421. (John Wiley & Sons Ltd.)XPS utilizing monochromatic Al Kα radiation has been employed to study metallic ruthenium and the catalytically and technol. important ruthenium compds. RuO2, RuCl3, Ru(NO)(NO3)3 and Ru(AcAc)3. The results improve on the accuracy of already published Ru(3d) binding energies, expand known Ru(3p) binding energies and also report spin-orbit splitting for the core levels. For RuO2, the difference between anhyd. and hydrated samples is explored, and the effect on curve fitting such spectra is discussed. Anal. of RuCl3 has allowed, for the first time, the pos. identification of Ru(OH)3 by XPS.
- 37Jiao, F.; Frei, H. Nanostructured manganese oxide clusters supported on mesoporous silica as efficient oxygen-evolving catalysts. Chem. Commun. 2010, 46, 2920– 2922, DOI: 10.1039/B921820C37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXksFOktbc%253D&md5=8b6ebf5f19915fa71b7ac271f92a5198Nanostructured manganese oxide clusters supported on mesoporous silica as efficient oxygen-evolving catalystsJiao, Feng; Frei, HeinzChemical Communications (Cambridge, United Kingdom) (2010), 46 (17), 2920-2922CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)Nanostructured Mn oxide clusters supported on mesoporous silica KIT-6 were characterized for generation of O2 in aq. soln. under visible light using tris(2,2'-bipyridine)Ru2+ photosensitizer and S2O82+ electron acceptor.
- 38Farges, F. Ab initio and experimental pre-edge investigations of the Mn K-edge XANES in oxide-type materials. Phys. Rev. B 2005, 71, 155109 DOI: 10.1103/PhysRevB.71.15510938https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXjvVeqtL8%253D&md5=201379adc3b902475bcdcd817004be65Ab initio and experimental pre-edge investigations of the Mn K-edge XANES in oxide-type materialsFarges, FrancoisPhysical Review B: Condensed Matter and Materials Physics (2005), 71 (15), 155109/1-155109/14CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)Mn K edge ab initio FEFF8.2 calcns. of the pre-edge features of the x-ray-absorption near-edge structure (XANES) region were undertaken for Mn-bearing oxide-type compds. The aim of the study is to provide a reliable method for detg. quant. and accurate redox and symmetry information for Mn. In agreement with multiplet calcns. by Glatzel and co-workers, FEFF8.2 predicts a doublet and a triplet for Mn(II) and Mn(III) in octahedral symmetry, resp., in agreement with high-resoln. XANES expts. Site distortion increases notably the contribution from dipolar transitions and, consequently, the pre-edge feature integrated area. An even more intense pre-edge feature is calcd. and measured for the Td symmetry (singletlike). For Mn(IV), a triplet is predicted and measured for the Oh symmetry. However, addnl. transitions are found in Mn(IV)-rich compds., that are related to metal-metal transitions. These transitions overlap strongly with the true pre-edge, making extn. of redox and symmetry information for Mn(IV) more challenging. However, a model of the pre-edge with pseudo-Voigt functions of fixed calcd. width (based on core-hole lifetime and exptl. resoln.) helps to sep. the contributions related to 1st-neighbor symmetry from those of the metal-metal pairs. Application to multivalent defective Mn oxide materials suggests that the pre-edge information varies linearly as a function of Mn redox state or symmetry but varies nonlinearly as a function of both parameters. Finally, the polymn. of the Mn networks can be estd. from the metal-metal transitions found in the pre-edge region.
- 39Ramírez, A.; Hillebrand, P.; Stellmach, D.; May, M. M.; Bogdanoff, P.; Fiechter, S. Evaluation of MnOx, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of Water. J. Phys. Chem. C 2014, 118, 14073– 14081, DOI: 10.1021/jp500939d39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXps1Wjsb0%253D&md5=bd3946f772340f9d4612c2fa1e54ff38Evaluation of MnOx, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of WaterRamirez, Alejandra; Hillebrand, Philipp; Stellmach, Diana; May, Matthias M.; Bogdanoff, Peter; Fiechter, SebastianJournal of Physical Chemistry C (2014), 118 (26), 14073-14081CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Different manganese oxide phases were prepd. as thin films to elucidate their structure-function relationship with respect to oxygen evolution in the process of water splitting. For this purpose, amorphous MnOx films anodically deposited on F:SnO2/glass and annealed at different temps. (to improve film adherence and crystallinity) were tested in neutral and alk. electrolytes. Differential electrochem. mass spectroscopy showed that the anodic current correlated well with the onset of the expected oxygen evolution, where in 1 M KOH, the anodic current of cryst. α-Mn2O3 films was detd. to onset at an overpotential (η) of 170 mVRHE (at J = 0.1 mA/cm2) with current densities of ca. 20 mA/cm2 at η = 570 mVRHE. Amorphous MnOx films heated at 573 K (MnOx-573 K) were found to improve their adherence to F:SnO2/glass substrate after heat treatment with a slight crystn. detected by Raman spectroscopy. The onset of water oxidn. of MnOx-573 K films was identified at η = 230 mVRHE (at J = 0.1 mA/cm2) with current densities of ca. 20 mA/cm2 at η = 570 mVRHE (1 M KOH). The least active of the investigated manganese oxides was Mn3O4 with an onset at η = 290 mVRHE (at J = 0.1 mA/cm2) and current densities of ca. 10 mA/cm2 at η = 570 mVRHE (1 M KOH). In neutral soln. (1 M KPi), a similar tendency was obsd. with the lowest overpotential found for α-Mn2O3 followed by MnOx-573 K and Mn3O4. XPS revealed that after electrochem. treatment, the surfaces of the manganese oxide electrodes exhibited oxidn. of Mn II and Mn III toward Mn IV under oxygen evolving conditions. In the case of α-Mn2O3 and MnOx-573 K, the manganese oxidn. was found to be reversible in KPi when switching the potential above and below the oxygen evolution reaction (OER) threshold potential. Furthermore, SEM (SEM) images displayed the presence of an amorphous phase on top of all manganese oxide films here tested after oxygen evolution. The results indicate that structural changes played an important role in the catalytic activity of the manganese oxides, in addn. to oxidn. states, a large variety of Mn-O bond lengths and a high concn. of oxygen point defects. Thus, compared to Mn3O4, cryst. α-Mn2O3 and MnOx-573 K are the most efficient catalyst for water oxidn. in the manganese-oxygen system.
- 40Mattelaer, F.; Bosserez, T.; Rongé, J.; Martens, J. A.; Dendooven, J.; Detavernier, C. Manganese oxide films with controlled oxidation state for water splitting devices through a combination of atomic layer deposition and post-deposition annealing. RSC Adv. 2016, 6, 98337– 98343, DOI: 10.1039/C6RA19188F40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1elsr%252FJ&md5=5cd3d443ea285849426fbed6611c13d4Manganese oxide films with controlled oxidation state for water splitting devices through a combination of atomic layer deposition and post-deposition annealingMattelaer, Felix; Bosserez, Tom; Ronge, Jan; Martens, Johan A.; Dendooven, Jolien; Detavernier, ChristopheRSC Advances (2016), 6 (100), 98337-98343CODEN: RSCACL; ISSN:2046-2069. (Royal Society of Chemistry)Solar hydrogen devices combine the power of photovoltaics and water electrolysis to produce hydrogen in a hybrid form of energy prodn. To engineer these into integrated devices (i.e. a water splitting catalyst on top of a PV element), the need exists for thin film catalysts that are both transparent for solar light and efficient in water splitting. Manganese oxides have already been shown to exhibit good water splitting performance, which can be further enhanced by conformal coating on high surface-area structures. The latter can be achieved by at. layer deposition (ALD). However, to optimize the catalytic and transparency properties of the water splitting layer, an excellent control over the oxidn. state of the manganese in the film is required. So far MnO, Mn3O4 and MnO2 ALD have been shown, while Mn2O3 is the most promising catalyst. Therefore, we investigated the post-deposition oxidn. and redn. of MnO and MnO2 ALD films, and derived strategies to achieve every phase in the MnO-MnO2 range by tuning the ALD process and post-ALD annealing conditions. Thin film Mn2O3 is obtained by thermal redn. of ALD MnO2, without the need for oxidative high temp. treatments. The obtained Mn2O3 is examd. for solar water splitting devices, and compared to the as-deposited MnO2. Both thin films show oxygen evolution activity and good solar light transmission.
- 41Liu, F.; Shan, W.; Lian, Z.; Xie, L.; Yang, W.; He, H. Novel MnWOx catalyst with remarkable performance for low temperature NH3-SCR of NOx. Catal. Sci. Technol. 2013, 3, 2699– 2707, DOI: 10.1039/C3CY00326D41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhsVSltr%252FL&md5=420d6c8f60cfe5bb2c2d63acedd0adabNovel MnWOx catalyst with remarkable performance for low temperature NH3-SCR of NOxLiu, Fudong; Shan, Wenpo; Lian, Zhihua; Xie, Lijuan; Yang, Weiwei; He, HongCatalysis Science & Technology (2013), 3 (10), 2699-2707CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)A novel W promoted MnOx catalyst (MnWOx) was used for the selective catalytic redn. (SCR) of NOx with NH3 at low temps., with high deNOx efficiency from 60 to 250 °C under relatively high space velocity. The MnWOx catalyst showed a unique core-shell structure with Mn3O4 covered by Mn5O8 while Mn4+ species at the outer surface served as a real active phase for NH3-SCR. The W doping resulted in the smaller particle size of MnOx active phase, increased the surface acidity and facilitated the NO/NH3 oxidn., thus enhancing low temp. deNOx efficiency by promoting both Langmuir-Hinshelwood and Eley-Rideal reaction pathways. This novel catalyst is promising to be used in the deNOx process for flue gas after dust removal and desulfurization.
- 42Wiechen, M.; Zaharieva, I.; Dau, H.; Kurz, P. Layered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashion. Chem. Sci. 2012, 3, 2330– 2339, DOI: 10.1039/C2SC20226C42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XotFGrsrs%253D&md5=82b5cc3945282c1bb968398e38403f4aLayered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashionWiechen, Mathias; Zaharieva, Ivelina; Dau, Holger; Kurz, PhilippChemical Science (2012), 3 (7), 2330-2339CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)In reaction sequences for light driven water-splitting into H2 and O2, water-oxidn. is a crucial reaction step. In vivo, the process is catalyzed within a photoenzyme called photosystem II (PSII) by a μ-oxido CaMn4 cluster, the oxygen-evolving complex (OEC). The OEC is known to be virtually inactive if Ca2+ is removed from its structure. Activity can be restored not only by the addn. of Ca2+ but also Sr2+ ions. We have recently introduced layered calcium manganese oxides of the birnessite mineral family as functional synthetic model compds. for the OEC. Here, we present the syntheses of layered manganese oxides where we varied the interlayer cations, prepg. a series of K-, Ca-, Sr- and Mg-contg. birnessites. Structural motifs within these materials were detd. using X-ray absorption spectroscopy (XAS) showing that all materials have similar at. structures despite their different elemental compns. Water-oxidn. expts. were carried out to elucidate structure-reactivity relations. These expts. demonstrated that the oxides-like the OEC-require the presence of calcium in their structures to reach max. catalytic activity. As another similarity to the OEC, Sr2+ is the "second best choice" for the secondary cation. The results thus support mechanistic proposals which involve an important catalytic role for Ca2+ in biol. water-oxidn. Addnl., they offer valuable hints for the development of synthetic, manganese-based water-oxidn. catalysts for artificial photosynthesis.
- 43Zahoransky, T.; Wegorzewski, A. V.; Huong, W.; Mikutta, C. X-ray absorption spectroscopy study of Mn reference compounds for Mn speciation in terrestrial surface environments. Am. Mineral. 2023, 108, 847– 864, DOI: 10.2138/am-2022-8236There is no corresponding record for this reference.
- 44Grangeon, S.; Lanson, B.; Miyata, N.; Tani, Y.; Manceau, A. Structure of nanocrystalline phyllomanganates produced by freshwater fungi. Am. Mineral. 2010, 95, 1608– 1616, DOI: 10.2138/am.2010.351644https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhsFSnsr3P&md5=0e7827b11ebade165c9092f0a9cbf5e3Structure of nanocrystalline phyllomanganates produced by freshwater fungiGrangeon, Sylvain; Lanson, Bruno; Miyata, Naoyuki; Tani, Yukinori; Manceau, AlainAmerican Mineralogist (2010), 95 (11-12), 1608-1616CODEN: AMMIAY; ISSN:0003-004X. (Mineralogical Society of America)The crystal structures of biogenic Mn oxides produced by three fungal strains isolated from stream pebbles were detd. using chem. analyses, XANES and EXAFS spectroscopy, and powder X-ray diffraction. The fungi-mediated oxidn. of aq. Mn2+ produces layered Mn oxides analogous to vernadite, a natural nanostructured and turbostratic variety of birnessite. The crystallites have domain dimensions of ∼10 nm in the layer plane (equiv. to ∼35 MnO6 octahedra), and ∼1.5-2.2 nm perpendicularly (equiv. to ∼2-3 layers), on av. The layers have hexagonal symmetry and from 22 to 30% vacant octahedral sites. This proportion likely includes edge sites, given the extremely small lateral size of the layers. The layer charge deficit, resulting from the missing layer Mn4+ cations, is balanced mainly by interlayer Mn3+ cations in triple-corner sharing position above and/or below vacant layer octahedra. The high surface area, defective crystal structure, and mixed Mn valence confer to these bio-minerals an extremely high chem. reactivity. They serve in the environment as sorption substrate for trace elements and possess catalytic redox properties.
- 45Zhang, A.; Zhao, R.; Hu, L.; Yang, R.; Yao, S.; Wang, S.; Yang, Z.; Yan, Y.-M. Adjusting the Coordination Environment of Mn Enhances Supercapacitor Performance of MnO2. Adv. Energy Mater. 2021, 11, 2101412 DOI: 10.1002/aenm.20210141245https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3MXhsVOku7zO&md5=ac9cf687f4a10228c82c3994eeffde60Adjusting the Coordination Environment of Mn Enhances Supercapacitor Performance of MnO2Zhang, Anqi; Zhao, Rui; Hu, Lingyuan; Yang, Ru; Yao, Shuyun; Wang, Shiyu; Yang, Zhiyu; Yan, Yi-MingAdvanced Energy Materials (2021), 11 (32), 2101412CODEN: ADEMBC; ISSN:1614-6840. (Wiley-Blackwell)The electrochem. properties of transition metal oxides strongly depend on the coordination environment of metal atoms. Nevertheless, the relationship between the coordination environment of metal atoms and electrochem. performance of metal oxides is unclear, while the strategy of adjusting the coordination environment of metal atoms is rare. Herein, the engineering of the coordination environment of Mn atoms in manganese dioxides (MnO2) by using a triethanolamine (TEA) complex-induced method is reported. The detailed exptl. characterizations and d. functional theory calcns. show that the optimized Mn coordination environment with oxygen deficiency and more corner-shared Mn-Mn shells results in apparent electron dislocation and forms an effective built-in elec. field. As a result, the obtained MnO2-TEA sample exhibits a high cond. and an excellent ion diffusion capacity, with a remarkable specific capacitance of 417.5 F g-1 at 1 A g-1. At the power d. of 450.0 W kg-1, the fabricated asym. supercapacitor delivers the maximal energy d. (57.4 Wh kg-1). This work not only provides an effective strategy of adjusting the coordination environment of metal atoms in metal oxides, but also presents a deeper understanding of the electronic structure dependent electrochem. performance of electrode materials.
- 46Gaillot, A.-C.; Flot, D.; Drits, V. A.; Manceau, A.; Burghammer, M.; Lanson, B. Structure of Synthetic K-rich Birnessite Obtained by High-Temperature Decomposition of KMnO4. I. Two-Layer Polytype from 800 °C Experiment. Chem. Mater. 2003, 15, 4666– 4678, DOI: 10.1021/cm021733g46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXoslWiurY%253D&md5=f050e4ffd26e1c9a5c6e62e63ec09110Structure of Synthetic K-rich Birnessite Obtained by High-Temperature Decomposition of KMnO4. I. Two-Layer Polytype from 800 °C ExperimentGaillot, Anne-Claire; Flot, David; Drits, Victor A.; Manceau, Alain; Burghammer, Manfred; Lanson, BrunoChemistry of Materials (2003), 15 (24), 4666-4678CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)The structure of a synthetic K birnessite (KBi) obtained as a finely dispersed powder by thermal decompn. of KMnO4 at 800° was for the 1st time studied by single-crystal XRD. KBi has a two-layer cell with a 2.840(1) and c 14.03(1) Å and space group P63/mmc. At. coordinates are given. In contrast to the structure model proposed by Kim et al. (Chem. Mater. 1999, 11, 557-563), the refined model demonstrates the sole presence of Mn4+ in the octahedral layers, the presence of 0.12 vacant layer sites per octahedron being responsible for the layer charge deficit. In agreement with x-ray absorption spectroscopy result, this layer charge deficit is compensated (1) by the presence of interlayer Mn3+ above or below vacant layer octahedra sharing three Olayer atoms with neighboring Mnlayer octahedra to form a triple-corner surface complex (VITC sites) and (2) by the presence of interlayer K in prismatic cavities located above or below empty tridentate cavities, sharing three edges with neighboring Mnlayer octahedra (VITE sites). As compared to the structure model proposed by Kim et al., this VITE site is shifted from the center of the prismatic cavity toward its edges. A complementary powder XRD study confirmed the structure model of the main defect-free KBi phase and allowed for the detn. of the nature of the stacking disorder in a defective accessory KBi phase admixed to the defect-free KBi.
- 47Krause, M. O.; Oliver, J. H. Natural widths of atomic K and L levels, Kα X-ray lines and several KLL Auger lines. J. Phys. Chem. Ref. Data 1979, 8, 329– 338, DOI: 10.1063/1.55559547https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1MXks1Gmu78%253D&md5=37bd4bfc06afcd12790698af09afd916Natural widths of atomic K and L levels, Kα x-ray lines and several KLL Auger linesKrause, M. O.; Oliver, J. H.Journal of Physical and Chemical Reference Data (1979), 8 (2), 329-38CODEN: JPCRBU; ISSN:0047-2689.Semi-empirical values of the natural widths of K, L1, L2 and L3 levels, and Kα2 x-ray lines, and KL1L1, KL1L2 and KL2L3 Auger lines for the elements 10 ≤ Z ≤ 110 are presented in tables and graphs. Level width Γi (i = K, L1, L2, L3) is obtained from the relation Γi = ΓR,i/ωi, using the theor. radiative rate ΓR,i from Scofield's relativistic, relaxed Hartree-Fock calcn. and the fluorescence yield ωi from Krause's evaluation. X-ray and Auger line widths are calcd. as the sums of pertinent level widths. This tabulation of natural level and line widths is internally consistent, and is compatible with all relevant exptl. and theor. information. Present semi-empirical widths, esp. those of Kα1 and Kα2 x-rays, are compared with measured widths. Uncertainties of semi-empirical values are estd.
- 48Otoyama, M.; Jacquet, Q.; Iadecola, A.; Saubanère, M.; Rousse, G.; Tarascon, J.-M. Synthesis and Electrochemical Activity of Some Na(Li)-Rich Ruthenium Oxides with the Feasibility to Stabilize Ru6+. Adv. Energy Mater. 2019, 9, 1803674 DOI: 10.1002/aenm.201803674There is no corresponding record for this reference.
- 49McKeown, D. A.; Hagans, P. L.; Carette, L. P. L.; Russell, A. E.; Swider, K. E.; Rolison, D. R. Structure of Hydrous Ruthenium Oxides: Implications for Charge Storage. J. Phys. Chem. B 1999, 103, 4825– 4832, DOI: 10.1021/jp990096n49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXjtFOlt78%253D&md5=1d15e92817fcf2876d9834be01d94588Structure of Hydrous Ruthenium Oxides: Implications for Charge StorageMcKeown, David A.; Hagans, Patrick L.; Carette, Linda P. L.; Russell, Andrea E.; Swider, Karen E.; Rolison, Debra R.Journal of Physical Chemistry B (1999), 103 (23), 4825-4832CODEN: JPCBFK; ISSN:1089-5647. (American Chemical Society)Hydrous ruthenium oxide (RuO2·xH2O or RuOxHy) is a mixed electron-proton conductor with a specific capacitance as high as 720 F/g/proton, making it a candidate material for energy storage. The correlation between the structure and properties of RuO2·xH2O materials is not well understood due to their amorphous nature and compositional variability. In this study, ruthenium oxides with the compns. RuO2·2.32H2O, RuO2·0.29H2O, and anhyd. RuO2 are characterized using thermogravimetric anal. (TGA), X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES) and extended X-ray fine structure (EXAFS) analyses. XANES cannot be used to distinguish between Ru(III) and Ru(IV) in the hydrous oxides, but the EXAFS analyses show large differences in the short-range structures of the materials. Whereas anhyd. RuO2 has the rutile structure comprising chains of RuO6 octahedra linked in three dimensions, the structure of RuO2·0.29H2O is rutile-like at the RuO6 core, but less connected and progressively disordered beyond the RuO6 core. The structure of RuO2·2.32H2O is composed of chains of disordered RuO6 octahedra that exhibit no chain-to-chain linking or three-dimensional order. Although the local structures of RuO2·0.29H2O and RuO2·2.32H2O markedly differ, their specific capacitances are large and essentially equiv., so nonunique local structures can balance effective electron transport (along dioxo bridges) with the effective proton transport (through structural water) necessary for charge storage.
- 50Qiu, J.-Z.; Hu, J.; Lan, J.; Wang, L.-F.; Fu, G.; Xiao, R.; Ge, B.; Jiang, J. Pure Siliceous Zeolite-Supported Ru Single-Atom Active Sites for Ammonia Synthesis. Chem. Mater. 2019, 31, 9413– 9421, DOI: 10.1021/acs.chemmater.9b0309950https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXitVOhsbbN&md5=247ff05f5ff8753e62044ea90a77218bPure Siliceous Zeolite-Supported Ru Single-Atom Active Sites for Ammonia SynthesisQiu, Jiang-Zhen; Hu, Jibo; Lan, Jinggang; Wang, Long-Fei; Fu, Guangying; Xiao, Rujian; Ge, Binghui; Jiang, JiuxingChemistry of Materials (2019), 31 (22), 9413-9421CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)As the most active new frontier, a single-atom catalyst (SAC) combining the merits of heterogeneous and homogeneous catalysts would have a significant effect on a 100-yr history of ammonia synthesis research. It is commonly accepted that B5 is the active site of Ru catalysts for ammonia synthesis. Here, the Ru single atoms catalyst has been demonstrated active and efficient for ammonia synthesis. To this end, an ideal model catalyst, pure siliceous zeolite-supported Ru SAC (Ru SAs/S-1), which shows surprising catalytic ammonia synthesis activity compared to that of a conventional Ru catalyst was designed. Both at. resoln. scanning transmission electron microscopy and X-ray absorption spectrometric anal. identify the single-Ru-atom nature of Ru SAs/S-1 before and after the reaction. Further DFT calcns. reveal that the reaction mechanism is different from traditional mechanisms. Therefore, beyond B5 sites, this paper provides an alternative SAC strategy to design high-performance Ru catalysts for ammonia synthesis.
- 51Matheu, R.; Ertem, M. Z.; Gimbert-Suriñach, C.; Sala, X.; Llobet, A. Seven Coordinated Molecular Ruthenium–Water Oxidation Catalysts: A Coordination Chemistry Journey. Chem. Rev. 2019, 119, 3453– 3471, DOI: 10.1021/acs.chemrev.8b0053751https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXjslyhurY%253D&md5=8013afd52a89cac003d9fa035a073cb9Seven Coordinated Molecular Ruthenium-Water Oxidation Catalysts: A Coordination Chemistry JourneyMatheu, Roc; Ertem, Mehmed Z.; Gimbert-Surinach, Carolina; Sala, Xavier; Llobet, AntoniChemical Reviews (Washington, DC, United States) (2019), 119 (6), 3453-3471CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Mol. H2O oxidn. catalysis is a field that has experienced an impressive development over the past decade mainly fueled by the promise of generation of sustainable C neutral fuel society, based on H2O splitting. Most of these advancements were possible thanks to the detailed understanding of the reactions and intermediates involved in the catalytic cycles. Today's best mol. H2O oxidn. catalysts reach turnover frequencies that are orders of magnitude higher than that of natural O evolving center in photosystem II. These catalysts are based on Ru complexes where at some stage, the 1st coordination sphere of the metal center becomes 7 coordinated. The key for this achievement is largely based on the use of adaptative ligands that adjust their coordination mode depending on the structural and electronic demands of the metal center at different oxidn. states accessed within the catalytic cycle. This Review covers the latest and most significant developments on Ru complexes that behave as powerful H2O oxidn. catalysts and where at some stage the Ru metal attains coordination no. 7. It provides a comprehensive and rational understanding of the different structural and electronic factors that govern the behavior of these catalysts.
Supporting Information
Supporting Information
ARTICLE SECTIONSThe Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsaem.3c01585.
Additional chronoamperometry, cyclic voltammetry, X-ray photoelectron spectroscopy, X-ray diffraction, EXAFS spectra, best fits and parameters for the first coordination shell, and fit results of the XANES spectrum of Mn 50 (PDF)
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