Manipulating Electrocatalysis using Mosaic Catalysts

Heterogeneous catalytic reactions play central roles in the production of chemicals and in energy-conversion systems. Much attention has been paid to improve the efficiency of heterogeneous catalysts under electrochemical environments for producing gas fuels, such as hydrogen (H2), oxygen (O2), methane (CH4), and carbon monoxide (CO). For example, the electrochemical hydrogen evolution is considered attractive due to the cleanliness and high energy density of hydrogen. Note that these heterogeneous catalytic reactions are usually slow in kinetics, making development of highefficiency catalysts the key in these fields. In recent years, the community has witnessed many successes in developing efficient electrocatalysts, including Pt and other noble metals, metal oxides, chalcogenides, carbides, and phosphides, among many others, for the gas-involved electrochemical reactions. These works have mostly focused on engineering chemical compositions (e.g., doping, alloying, and phase-changing engineering) and/ or physical features (e.g., size, shape, and strain engineering) of the catalysts, by which the bonding strength between reaction intermediates and catalysts can be modulated so as to improve the catalytic performance. For example, Lukowski et al. reported that molybdenum disulfide shows a decreased overpotential for hydrogen evolution reaction (HER) when changed from semiconducting 2 H phase to metallic 1 T phase. In another work, the electronic structures of atomically dispersed Ru catalysts are precisely modulated by coating metal shells, which exert a proper compressive strain on Ru, resulting in a low overpotential of 220mV@10mA cm 2 for oxygen evolution reaction (OER). These methods are interesting, while modulating the electronic structures of catalysts via chemical compositions and physical features at the atomic level is challenging. It is therefore interesting to explore a simple strategy to engineer the performance of electrocatalysts. In general, electrochemical process is affected by factors including the chemistry, microscopic structure, geometry of catalysts, etc., which thus can be used to improve catalytic performance. This fact gives new opportunities in modulating the performance of electrocatalysts besides chemistry. Here, instead of focusing on the chemical component and nanostructure of the catalysts, we design a type of mosaic catalyst and demonstrate that the spatial structure of the catalyst is another degree of freedom to modulate the performance of electrocatalysts. There are three advantages of engineering the spatial structures of catalysts in improving their performance. First, the design of spatial structures can be combined with other strategies (e.g., doping, alloying, and strain engineering) to further improve the catalytic performance. Second, this method is suitable for Dr. Y. Luo, L. Tang, Z. Zhang, F. Yang, Dr. Q. Yu, Dr. B. Ding, Prof. B. Liu Shenzhen Geim Graphene Center (SGC) Tsinghua-Berkeley Shenzhen Institute (TBSI) and Tsinghua Shenzhen International Graduate School (TSIGS) Tsinghua University Shenzhen 518055, P. R. China E-mail: bilu.liu@sz.tsinghua. edu.cn Prof. S. W. Chiang Tsinghua Shenzhen International Graduate School (TSIGS) Tsinghua University Shenzhen 518055, P. R. China