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High entropy materials (HEM) have been attracting much attention as emerging catalysts for electrochemical water splitting. HEM catalysts have unique properties such as an interesting cocktail effect, broad design space, customizable electronic structure, and excellent entropy stabilization effect compared with single-digit catalysts. This paper provides a comprehensive overview of the use of HEM as a catalyst for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water splitting. HEM design strategies including phase structure modulation, defect engineering, electrode configuration engineering, and computational aids are discussed to develop HEM catalysts with high performance and stability. In particular, the importance of density functional theory, high-throughput screening techniques, and machine learning for the discovery and design of HEM catalysts is emphasized. Finally, the challenges and imminent difficulties are prospected, and the corresponding strategies to deal with these challenges are put forward to promote the development of HEM catalysts in the field of electrochemical water splitting. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospects and electrochemical performance of hydrogen evolution catalysts, extensive research on transition metal materials has been carried out. Among the many catalytic materials, cobalt is an element with potential for the hydrogen evolution reaction (HER) due to its abundant reserves, low cost, and small energy barrier for H adsorption. This review classifies the latest research on cobalt-based catalysts according to the types of compound, including cobalt-based sulfides, phosphides, carbides, borides, oxides, etc., and summarizes the latest research progress of cobalt-based compound catalysts in acidic and alkaline media. Strategies to tune the properties of cobalt-based compound catalysts for high catalytic activity for HER are focused on, including structural engineering, defect engineering, and doping, etc. The advantages and limitations of each modified approach are reviewed. Not only that, but also the catalytic activity and advantages of the catalyst are evaluated by using density functional theory (DFT) calculation-related descriptors, activity evaluation parameters, etc. Finally, limitations and challenges of cobalt-based materials for HER are presented, as well as prospects for future research. This paper aims to understand the chemical and physical factors that affect cobalt-based catalysts, and to find directions for future research on cobalt-based catalysts. [ABSTRACT FROM AUTHOR]