An overview of the active sites in transition metal electrocatalysts and their practical activity for hydrogen evolution reaction

Locating the active sites and understanding the reaction mechanism are crucial for the design and preparation of higher hydrogen evolution activity catalysts. If these theoretical knowledges can be combined with practical large-scale hydrogen production, the development of electrochemical water splitting will be further promoted. In this review, we have first summarized the active sites of recent reported HER catalysts, including transition metals molybdenum, iron, nickel, cobalt and noble metal-based materials. At the same time, the mechanisms of hydrogen evolution followed by each catalyst and corresponding strategies for improving their catalytic activity are also discussed. In addition, from the point of practical application, the testing conditions, achievements already made and challenges that to be faced for each type of material are also proposed. The implementation of this work is helpful for researchers to master the electrocatalyst from a deeper perspective (including hydrogen adsorption energy, water adsorption energy, water dissociation energy, active surface and active site.), thus promoting the development of water electrolysis.