Electronic structural engineering of transition metal-based electrocatalysts for the hydrogen evolution reaction

The hydrogen evolution reaction (HER) in water splitting is vital to the production of high-purity hydrogen from sustainable energy sources in order to combat climate change and environmental crises resulting from combustion of conventional fossil fuels. However, HER suffers from sluggish electrochemical reactions as well as expensive precious metal-based catalysts. Inexpensive transition metals and their compounds are desirable substitutes for precious-metal-based compounds for HER. Several strategies have been proposed to modulate the electronic configuration to improve the catalytic properties because the electronic structure contributes significantly to the electrocatalytic activity. Herein, we describe the effects and mechanism of the electronic structure on the electrocatalytic activity and discuss viable strategies to modulate the electronic configuration of electrocatalysts by means of doping, vacancies, heterostructures, strain, and phase engineering. In addition, the advantages and disadvantages of each strategy as well as challenges and prospective of transition metal-based HER catalysts are discussed.