Earth-Abundant Amorphous Electrocatalysts for Electrochemical Hydrogen Production: A Review

Electrochemical water splitting provides a promising approach to store renewable electricity in the form of hydrogen on a grand scale. However, the current techniques for large-scale electrochemical hydrogen production rely on the use of expensive and scarce noble-metal catalysts making it uncompetitive to traditional methods using fossil fuels. Thus, replacing noble-metal electrocatalysts with cheap materials made of abundant elements holds the key to achieve the cost-effectiveness. Recently, amorphous electrocatalysts emerged as promising candidates due to their unique physical and chemical properties compared with their crystalline counterparts leading to superior catalytic performance. Given the rapid advances made in the design, synthesis, and development of amorphous catalysts, namely monometallic and multimetallic borides, sulfides, phosphides, oxides, and hydroxides based on transition metals, the recent progress on compositional designs, microstructure, morphology, electronic properties, and interaction with host materials are reviewed critically. Special attention is paid to uncover the main strategies adopted in each material category and the underlying structure–property relationship that lead to improved hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. As a result, guidance for the design and synthesis of novel amorphous electrocatalysts with high performance for large-scale electrochemical water splitting application is provided.