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

This article references 51 other publications.

1. 1

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   Recent progress in alkaline water electrolysis for hydrogen production and applications

   Zeng, Kai; Zhang, Dongke

   Progress 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.

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2. 2

   Rao, 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/C7EE02307C

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   Towards identifying the active sites on RuO2(110) in catalyzing oxygen evolution

   Rao, 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, Yang

   Energy & 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.

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   Demirbas, A. Future hydrogen economy and policy. Energy Sources, Part B 2017, 12, 172– 181,  DOI: 10.1080/15567249.2014.950394

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   Future hydrogen economy and policy

   Demirbas, Ayhan

   Energy 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.

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   Benck, 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/cs500923c

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   Catalyzing the Hydrogen Evolution Reaction (HER) with Molybdenum Sulfide Nanomaterials

   Benck, 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.

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5. 5

   Shi, 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/C8EE01111G

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   Rapid flame doping of Co to WS2 for efficient hydrogen evolution

   Shi, Xinjian; Fields, Meredith; Park, Joonsuk; McEnaney, Joshua M.; Yan, Hongping; Zhang, Yirui; Tsai, Charlie; Jaramillo, Thomas F.; Sinclair, Robert; Noerskov, Jens K.; Zheng, Xiaolin

   Energy & 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.

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   Lyons, 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.2016.12.005

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   Recent developments in electrochemical water oxidation

   Lyons, 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.

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7. 7

   Cherevko, 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.2015.08.014

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   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

   Cherevko, 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.

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8. 8

   Sayeed, 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/C5TA09125J

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   Direct electrochemical formation of nanostructured amorphous Co(OH)2 on gold electrodes with enhanced activity for the oxygen evolution reaction

   Sayeed, 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.

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9. 9

   Pei, 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.7b09282

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   Controlled Electrodeposition Synthesis of Co-Ni-P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water Splitting

   Pei, Yu; Yang, Yang; Zhang, Fangfang; Dong, Pei; Baines, Robert; Ge, Yuancai; Chu, Hang; Ajayan, Pulickel M.; Shen, Jianfeng; Ye, Mingxin

   ACS 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.

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10. 10

    Escudero-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 IrO_x in Stabilizing RuO₂ for Oxygen Evolution. J. Phys. Chem. B 2018, 122, 947– 955,  DOI: 10.1021/acs.jpcb.7b07047

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    Importance of Surface IrOx in Stabilizing RuO2 for Oxygen Evolution

    Escudero-Escribano, Maria; Pedersen, Anders F.; Paoli, Elisa A.; Frydendal, Rasmus; Friebel, Daniel; Malacrida, Paolo; Rossmeisl, Jan; Stephens, Ifan E. L.; Chorkendorff, Ib

    Journal 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.

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11. 11

    Browne, 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.2017.10.011

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    A mechanical, high surface area and solvent-free 'powder-to-electrode' fabrication method for screening OER catalysts

    Browne, 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.

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12. 12

    Stoerzinger, 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/jz500610u

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    Orientation-Dependent Oxygen Evolution Activities of Rutile IrO2 and RuO2

    Stoerzinger, Kelsey A.; Qiao, Liang; Biegalski, Michael D.; Yang, Shao-Horn

    Journal 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.

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13. 13

    Gao, 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.201600525

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    Hierarchical NiCo2O4 Hollow Microcuboids as Bifunctional Electrocatalysts for Overall Water-Splitting

    Gao, Xuehui; Zhang, Hongxiu; Li, Quanguo; Yu, Xuegong; Hong, Zhanglian; Zhang, Xingwang; Liang, Chengdu; Lin, Zhan

    Angewandte 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.

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14. 14

    Etzi 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.2019.118225

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    Mn promotion of rutile TiO2-RuO2 anodes for water oxidation in acidic media

    Etzi 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.

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15. 15

    Browne, 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.5b02069

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    Low-Overpotential High-Activity Mixed Manganese and Ruthenium Oxide Electrocatalysts for Oxygen Evolution Reaction in Alkaline Media

    Browne, 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.

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16. 16

    Browne, 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.201600370

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    Thermally prepared Mn2O3 /RuO2/Ru thin films as highly active catalysts for the Oxygen Evolution Reaction in Alkaline Media

    Browne, Michelle; Nolan, Hugo; Twamley, Brendan; Duesberg, Georg; Colavita, Paula; Lyons, Michael

    ChemElectroChem (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.

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17. 17

    Wu, 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.9b04237

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    17

    Bimetallic Doped RuO2 with Manganese and Iron as Electrocatalysts for Favorable Oxygen Evolution Reaction Performance

    Wu, Yiyi; Tariq, Muhammad; Zaman, Waqas Qamar; Sun, Wei; Zhou, Zhenhua; Yang, Ji

    ACS 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.

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18. 18

    Lin, 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/s41929-021-00703-0

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    18

    In-situ reconstructed Ru atom array on α-MnO2 with enhanced performance for acidic water oxidation

    Lin, 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-Ho

    Nature 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.

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19. 19

    Gorlin, 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/ja3104632

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    19

    In Situ X-ray Absorption Spectroscopy Investigation of a Bifunctional Manganese Oxide Catalyst with High Activity for Electrochemical Water Oxidation and Oxygen Reduction

    Gorlin, 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.

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20. 20

    Frydendal, R.; Seitz, L. C.; Sokaras, D.; Weng, T.-C.; Nordlund, D.; Chorkendorff, I.; Stephens, I. E. L.; Jaramillo, T. F. Operando investigation of Au-MnO_x thin films with improved activity for the oxygen evolution reaction. Electrochim. Acta 2017, 230, 22– 28,  DOI: 10.1016/j.electacta.2017.01.085

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    20

    Operando investigation of Au-MnOx thin films with improved activity for the oxygen evolution reaction

    Frydendal, 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.

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21. 21

    Lian, 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/C7SE00086C

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    21

    Template-free synthesis of mesoporous manganese oxides with catalytic activity in the oxygen evolution reaction

    Lian, 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.

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22. 22

    Petrykin, V.; Bastl, Z.; Franc, J.; Macounova, K.; Makarova, M.; Mukerjee, S.; Ramaswamy, N.; Spirovova, I.; Krtil, P. Local Structure of Nanocrystalline Ru_1–xNi_xO₂–δ Dioxide and Its Implications for Electrocatalytic Behavior─An XPS and XAS Study. J. Phys. Chem. C 2009, 113, 21657– 21666,  DOI: 10.1021/jp904935e

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    22

    Local Structure of Nanocrystalline Ru1-xNixO2-δ Dioxide and Its Implications for Electrocatalytic Behavior - An XPS and XAS Study

    Petrykin, 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.

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23. 23

    Seitz, 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.2016.01.200

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    23

    Tuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution Reaction

    Seitz, 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.

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24. 24

    Abbott, 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.6b02625

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    24

    Iridium Oxide for the Oxygen Evolution Reaction: Correlation between Particle Size, Morphology, and the Surface Hydroxo Layer from Operando XAS

    Abbott, 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.

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25. 25

    Gorlin, 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/ja407581w

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    25

    Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation

    Gorlin, 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.

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26. 26

    Petrykin, 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.2012.03.075

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    26

    Local structure of Co doped RuO2 nanocrystalline electrocatalytic materials for chlorine and oxygen evolution

    Petrykin, Valery; Macounova, Katerina; Okube, Maki; Mukerjee, Sanjeev; Krtil, Petr

    Catalysis 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.

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27. 27

    Petrykin, 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.200907128

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    27

    Tailoring the selectivity for electrocatalytic oxygen evolution on ruthenium oxides by zinc substitution

    Petrykin, V.; Macounova, K.; Shlyakhtin, O. A.; Krtil, Petr

    Angewandte 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.

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28. 28

    Biesinger, 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.2010.07.086

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    28

    Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn

    Biesinger, 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.

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29. 29

    Newville, M. EXAFS analysis using FEFF and FEFFIT. J. Synchrotron Radiat. 2001, 8, 96– 100,  DOI: 10.1107/S0909049500016290

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    EXAFS analysis using FEFF and FEFFIT

    Newville, Matthew

    Journal 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.

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30. 30

    Newville, M. IFEFFIT: interactive XAFS analysis and FEFF fitting. J. Synchrotron Radiat. 2001, 8, 322– 324,  DOI: 10.1107/S0909049500016964

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    IFEFFIT: interactive XAFS analysis and FEFF fitting

    Newville, Matthew

    Journal 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.

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31. 31

    Diebold, U.; Madey, T. E. TiO₂ by XPS. Surf. Sci. Spectra 1996, 4, 227– 231,  DOI: 10.1116/1.1247794

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    Di 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-X

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    XPS study of manganese monoxide oxidation

    Di 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.

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33. 33

    Biesinger, 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.2010.10.051

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    Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni

    Biesinger, 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.

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34. 34

    Wöllner, 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-C

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    Wei, 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/jp0479522

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    Effects of Ni Doping on [MnO6] Octahedron in LiMn2O4

    Wei, 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).

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36. 36

    Morgan, D. J. Resolving ruthenium: XPS studies of common ruthenium materials. Surf. Interface Anal. 2015, 47, 1072– 1079,  DOI: 10.1002/sia.5852

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    Resolving ruthenium: XPS studies of common ruthenium materials

    Morgan, 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.

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37. 37

    Jiao, 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/B921820C

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    Nanostructured manganese oxide clusters supported on mesoporous silica as efficient oxygen-evolving catalysts

    Jiao, Feng; Frei, Heinz

    Chemical 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.

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38. 38

    Farges, 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.71.155109

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    38

    Ab initio and experimental pre-edge investigations of the Mn K-edge XANES in oxide-type materials

    Farges, Francois

    Physical 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.

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39. 39

    Ramírez, A.; Hillebrand, P.; Stellmach, D.; May, M. M.; Bogdanoff, P.; Fiechter, S. Evaluation of MnO_x, Mn₂O₃, and Mn₃O₄ Electrodeposited Films for the Oxygen Evolution Reaction of Water. J. Phys. Chem. C 2014, 118, 14073– 14081,  DOI: 10.1021/jp500939d

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    39

    Evaluation of MnOx, Mn2O3, and Mn3O4 Electrodeposited Films for the Oxygen Evolution Reaction of Water

    Ramirez, Alejandra; Hillebrand, Philipp; Stellmach, Diana; May, Matthias M.; Bogdanoff, Peter; Fiechter, Sebastian

    Journal 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.

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40. 40

    Mattelaer, 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/C6RA19188F

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    40

    Manganese oxide films with controlled oxidation state for water splitting devices through a combination of atomic layer deposition and post-deposition annealing

    Mattelaer, Felix; Bosserez, Tom; Ronge, Jan; Martens, Johan A.; Dendooven, Jolien; Detavernier, Christophe

    RSC 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.

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41. 41

    Liu, F.; Shan, W.; Lian, Z.; Xie, L.; Yang, W.; He, H. Novel MnWO_x catalyst with remarkable performance for low temperature NH₃-SCR of NO_x. Catal. Sci. Technol. 2013, 3, 2699– 2707,  DOI: 10.1039/C3CY00326D

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    41

    Novel MnWOx catalyst with remarkable performance for low temperature NH3-SCR of NOx

    Liu, Fudong; Shan, Wenpo; Lian, Zhihua; Xie, Lijuan; Yang, Weiwei; He, Hong

    Catalysis 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.

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42. 42

    Wiechen, 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/C2SC20226C

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    42

    Layered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashion

    Wiechen, Mathias; Zaharieva, Ivelina; Dau, Holger; Kurz, Philipp

    Chemical 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.

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43. 43

    Zahoransky, 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-2022-8236

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44. 44

    Grangeon, 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.2010.3516

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    44

    Structure of nanocrystalline phyllomanganates produced by freshwater fungi

    Grangeon, Sylvain; Lanson, Bruno; Miyata, Naoyuki; Tani, Yukinori; Manceau, Alain

    American 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.

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45. 45

    Zhang, 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.202101412

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    45

    Adjusting the Coordination Environment of Mn Enhances Supercapacitor Performance of MnO2

    Zhang, Anqi; Zhao, Rui; Hu, Lingyuan; Yang, Ru; Yao, Shuyun; Wang, Shiyu; Yang, Zhiyu; Yan, Yi-Ming

    Advanced 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.

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46. 46

    Gaillot, 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/cm021733g

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    46

    Structure of Synthetic K-rich Birnessite Obtained by High-Temperature Decomposition of KMnO4. I. Two-Layer Polytype from 800 °C Experiment

    Gaillot, Anne-Claire; Flot, David; Drits, Victor A.; Manceau, Alain; Burghammer, Manfred; Lanson, Bruno

    Chemistry 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.

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    Krause, M. O.; Oliver, J. H. Natural widths of atomic K and L levels, K_α X-ray lines and several KLL Auger lines. J. Phys. Chem. Ref. Data 1979, 8, 329– 338,  DOI: 10.1063/1.555595

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    Natural widths of atomic K and L levels, Kα x-ray lines and several KLL Auger lines

    Krause, 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.

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    Otoyama, 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.201803674

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    McKeown, 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/jp990096n

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    Structure of Hydrous Ruthenium Oxides: Implications for Charge Storage

    McKeown, 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.

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    Qiu, 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.9b03099

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    Pure Siliceous Zeolite-Supported Ru Single-Atom Active Sites for Ammonia Synthesis

    Qiu, Jiang-Zhen; Hu, Jibo; Lan, Jinggang; Wang, Long-Fei; Fu, Guangying; Xiao, Rujian; Ge, Binghui; Jiang, Jiuxing

    Chemistry 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.

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    Matheu, 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.8b00537

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    Seven Coordinated Molecular Ruthenium-Water Oxidation Catalysts: A Coordination Chemistry Journey

    Matheu, Roc; Ertem, Mehmed Z.; Gimbert-Surinach, Carolina; Sala, Xavier; Llobet, Antoni

    Chemical 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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