Precious metal-free approach to hydrogen electrocatalysis for energy conversion: From mechanism understanding to catalyst design

Hydrogen (H-2) is the most promising green energy resources to replace conventional fossil fuels due to the high mass energy density and renewability. The hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) are two reactions that play key roles in electrochemical energy storage and conversion with the sustainable H-2 as a medium. To date, the most efficient catalysts for production and conversion of hydrogen are based on noble metals. Therefore, the development of non-noble metal catalysts with high efficiency and low cost is of significant importance for the practical application of H-2 in different electrochemical energy technologies. In this review, we recapitulate the recent progress of developing non-noble metal-based electrocatalysts for HER and HOR and provide insights into the origins of catalytic performance enhancement. Fundamental understanding of the synthesis-structure-activity correlations, focusing on the HER/HOR mechanisms in acidic/alkaline media on studied non-noble metal catalysts are also discussed.