Transition-metal selenides in hydrogen and oxygen electrocatalysis

Transition-metal selenides (TMSes) are attracting increasing interest as electrocatalysts owing to the covalent nature of the metal–Se bond and the polarizable Se sublattice, which collectively reshape charge distribution and adsorption energetics at working interfaces. This review summarizes the recent progress of TMSes as effective catalysts or pre-catalysts for hydrogen and oxygen electrocatalysis, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which are the core reactions for water electrolysis, fuel cells and metal-air batteries. Particular emphasis is placed on the correlations between electronic/interfacial structures and catalytic activity, selectivity, and stability to highlight recurring trends and existing limitations. Furthermore, the commonly employed regulation strategies, including chemical doping, heterointerface engineering and phase regulation, are summarized and their effectiveness compared. Practical concerns regarding stability/dissolution, selenium utilization and safety, as well as inconsistencies in benchmarking protocols, are also discussed. Finally, future perspectives on the development of TMSes as efficient, durable, and cost-competitive electrocatalysts are outlined.