Recent advances in mechanistic understanding and catalyst design for alkaline hydrogen evolution reactions

Hydrogen produced through water electrolysis is emerging as a highly promising alternative to the current hydrocarbon fuels. The hydrogen evolution reaction (HER) plays a pivotal role as a cathodic reaction in electrolysers. Unfortunately, the reaction kinetics of the HER under alkaline conditions is significantly slow, which has impeded the progress of water electrolysis technology for the production of high-purity hydrogen. In contrast to the well-known acidic HER, the mechanistic understanding of the alkaline HER remains controversial, requiring focused efforts to improve its sluggish kinetics. In order to understand the constraints of the alkaline HER and advance its development, this review article provides a critical assessment of the alkaline HER, with specific emphasis on the kinetics of the surface reaction. In particular, it addresses avenues for improving the intrinsic electronic structure of catalytic materials to achieve desirable interactions at the interfaces between catalysts and reaction intermediates. By elucidating several examples through theoretical calculations, surface characterization, and electrochemical experiments, we aim to highlight key elements of the ongoing debate and furnish a more comprehensive understanding of alkaline HERs. This review presents recent progress in alkaline HERs, covering mechanistic insights, catalyst development, and device performance. It also addresses challenges and future directions for high-performance alkaline HER catalysts.