Efficient and stable electrocatalysts for water splitting
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Introduction The water dissociation process, also known as “water splitting,” provides a fascinating and promising technology to convert renewable electricity into storable chemical energy, including hydrogen and oxygen collected at the device anode and cathode, respectively. Development has exploded in this energy-harvesting technology. There are many materials innovations to explore breakthroughs in achieving cost-effective, highly efficient, and durable electrocatalysts to maximize the energy-conversion efficiency of water splitting. In general, electrocatalysts can be rationally designed based on the feedback-loop approach as illustrated in Figure 1, including (1) running a large number of design of experiments (DOEs) and establishing a materials library of catalytically active elements; (2) utilizing the library’s information resources to fabricate different catalysts with desired properties via various synergistic strategies, followed by the systematic evaluation of their electrochemical parameters and corresponding electrocatalytic mechanisms; and (3) combining with complementary experimental and theoretical investigations to identify activity descriptors for the catalyst material system that can be employed to describe and/or predict the catalytic performance, thus further enhance catalytic performance and operational stability. These findings provide valuable feedback to the materials library to complete the design loop.
Despite the progress achieved by the above mentioned strategies in recent years, several key issues remain for insufficient electrochemical performance of the obtained catalysts. For example, the use of strongly acidic and alkaline electrolytes as well as precious metal (i.e., Ir and Pt)-based active materials would restrict the large-scale practical utilization of electrocatalysts. When non-noble electrocatalysts are employed, the large overpotential along with high energy loss, poor stability, and narrow pH operating range would inevitably limit applications. In order to overcome these obstacles, three methods are widely adopted to improve the electrochemical performance of catalysts. First, the intrinsic activity of catalyst active sites can be substantially increased with different electronic structure engineering strategies, including cation/anion doping, defect engineering, crystal phase and facet manipulation, and surface strain modification. Second, the exposure of these active sites can be greatly enlarged using various catalyst morphology designs. Finally, charge-transfer efficiency can be significantly improved by directly depositing catalysts onto hierarchical conducting support substrates.1 In this case, the advanced materials revolution would totally change the paradigm in electrocatalyst design to achieve efficient and robust water splitting. The articles in this issue highlight recent advances in materials innovations of electrocatalysts. These include rational
Xiuming Bu, Department of Materials Science and Engineering, City University of Hong Kong, Hong Kong; xiumingbu2
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