Advanced MOF-based electrode materials for supercapacitors and electrocatalytic oxygen reduction 超级电容器和电催化氧还原的先进 MOF 基电极材料
Bolong Yang , Bingjie Li , and Zhonghua Xiang 杨伯龙 ，李冰洁 ，向中华 State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China 北京化工大学有机-无机复合材料国家重点实验室，中国北京 100029 The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450052, China 郑州大学第一附属医院，中国郑州 450052 Bolong Yang and Bingie Li contributed equally to this work. 杨博龙和李冰洁对这项工作贡献相同。
Metal-organic frameworks (MOFs) have attracted a lot of attention due to their diverse structures, favorable porous properties, and tunable chemical compositions in the multiple fields. Notably, MOF-based materials (including pristine MOFs, MOF composites, and their derivatives) play the vital role in electrochemical energy storage and conversion systems, due to their ability for regulating chemical composition at the molecular level and their highly porous frameworks for facilitating the mass and charge transfer. Supercapacitors and fuel cells are used as one of energy storage and conversion systems respectively, and it is unstoppable to design and synthesize high-efficiency electrode materials for them. This review starts with the strategies for designing targeted MOF-based materials in electrochemical energy storage and conversion applications followed by the state-ofthe-art MOF-based materials discussed as to their potential applications in supercapacitors and electrocatalytic oxygen reduction reaction (ORR). Finally, the challenges and perspectives of MOF-based materials applied for supercapacitors and electrocatalytic ORR are discussed. 金属有机框架（MOFs）因其多样的结构、有利的多孔性能和可调节的化学组成在多个领域引起了广泛关注。值得注意的是，基于 MOF 的材料（包括原始 MOFs、MOF 复合材料及其衍生物）在电化学能量存储和转化系统中发挥着至关重要的作用，这是因为它们能够在分子水平上调节化学组成，并具有高度多孔的框架以促进质量和电荷传输。超级电容器和燃料电池分别用作能量存储和转化系统之一，为它们设计和合成高效电极材料势在必行。本综述从设计针对性的基于 MOF 的材料在电化学能量存储和转化应用中的策略开始，然后讨论了最新的基于 MOF 的材料，以及它们在超级电容器和电催化氧还原反应（ORR）中的潜在应用。最后，讨论了基于 MOF 的材料在超级电容器和电催化 ORR 中应用所面临的挑战和展望。
Since the industrial revolution, a large amount of fossil fuels have been consumed to promote economic development and brought unprecedented prosperity to human society . The combustion of these fuels will inevitably emit a massive amount of carbon dioxide, which is considered the main greenhouse gas leading to global warming . The comprehensive strategy to address climate change is to build a clean, low-carbon, safe, and efficient energy system by improving the utilization of renewable and environmentally friendly energy sources and storage devices, to achieve carbon neutralization as soon as possible . Electrochemical energy storage and conversion technologies have been recognized as the most practical choice to alleviate the increasingly serious energy crisis and environmental damage due to their high energy conversion efficiency and low environmental pollution . As a result, efforts are being made to promote sustainable energy storage and conversion systems, such as supercapacitors and fuel cells. The former is the main energy storage system, in which advanced electrode materials with high specific capacitance (SC) and durability are highly desired . The latter is the main energy conversion system, in which functional electrocatalysts with high activity and stability are essential [11]. Although the working principles of these electrochemical systems are different, they all have the similar pursuit for the physicochemical properties of materials, such as high specific surface area (SSA), good electrical conductivity, hierarchical porous structure, excellent electrocatalytic activity and selectivity, and long-term stability, which determines their ultimate storage capacity and conversion efficiency in electrochemical energy storage and conversion devices . Therefore, looking for new functional materials with ideal composition and structure has always been the top priority of future electrochemical energy storage and conversion technology. 自工业革命以来，大量化石燃料被消耗以促进经济发展，并给人类社会带来了前所未有的繁荣。燃烧这些燃料必然会排放大量二氧化碳，被认为是导致全球变暖的主要温室气体。应对气候变化的综合策略是通过提高可再生和环保能源源和储能设备的利用，建立一个清洁、低碳、安全、高效的能源系统，尽快实现碳中和。电化学能量存储和转换技术被认为是缓解日益严重的能源危机和环境破坏的最实用选择，因为它们具有高能量转换效率和低环境污染。因此，正在努力推广可持续的能量存储和转换系统，如超级电容器和燃料电池。 前者是主要的能量存储系统，其中具有高比电容（SC）和耐久性的先进电极材料备受追求。后者是主要的能量转换系统，其中具有高活性和稳定性的功能性电催化剂至关重要。尽管这些电化学系统的工作原理不同，但它们都对材料的物理化学性质有类似的追求，如高比表面积（SSA）、良好的电导率、分级多孔结构、优异的电催化活性和选择性，以及长期稳定性，这些性质决定了它们在电化学能量存储和转换设备中的最终存储容量和转换效率。因此，寻找具有理想组成和结构的新功能材料一直是未来电化学能量存储和转换技术的首要任务。
Metal-organic frameworks (MOFs) are a class of crystalline porous polymers with periodic network structures formed by metal ions (or metal clusters) and organic ligands. MOFs are considered one of the best links between nanotechnology and energy storage due to their high specific surface area, abundant pores, controllable morphology, and multi-functionalities [14-16]. Up to now, more than 20,000 MOFs with diverse crystal structures, compositions, and morphologies have been discovered and this number is still increasing. Several MOFs have been directly used as electrode materials for supercapacitors and electrocatalytic oxygen reduction reaction (ORR) [17]. The use of pristine MOFs with high surface area and the large diversity of metal ions as electrode materials for supercapacitors shows great potential and advantages. When using pure MOFs as electrode materials, low chemical stability and lack of electrical conductivity are the two key problems that have to face. So some MOFs are also used as supports to composite with active nanomaterials to solve above problems, including the combination of MOF and carbon materials (active carbon ( ), carbon nanotubes (CNTs), 金属有机框架（MOFs）是一类由金属离子（或金属团簇）和有机配体形成的具有周期性网络结构的结晶多孔聚合物。由于其高比表面积、丰富孔隙、可控形态和多功能性，MOFs 被认为是纳米技术和能量存储之间最好的联系之一。到目前为止，已经发现了超过 20,000 种具有不同晶体结构、组成和形态的 MOFs，这个数字仍在增加。一些 MOFs 已直接用作超级电容器和电催化氧还原反应（ORR）的电极材料。使用具有高比表面积和多样化金属离子的原始 MOFs 作为超级电容器的电极材料显示出巨大的潜力和优势。当将纯 MOFs 用作电极材料时，低化学稳定性和缺乏电导率是必须面对的两个关键问题。因此，一些 MOFs 也被用作支撑材料，与活性纳米材料复合以解决上述问题，包括 MOF 与碳材料（活性炭、碳纳米管）。