Development and perspectives of multi-site electrocatalysts for neutral hydrogen evolution

Hydrogen is a green and efficient energy candidate for the sustainable development of society. The electrocatalytic hydrogen evolution reaction (HER) of water splitting is a facile and sustainable approach to produce high-purity green hydrogen with zero carbon emission. Compared with the strong corrosivity of acidic/alkali electrolytes, water splitting in neutral electrolytes is a more promising choice, since it provides a mild environment for large-scale hydrogen production. Multi-site engineering is one of the most effective strategies for improving the neutral HER activity, because the neutral HER involves water dissociation and hydrogen adsorption/desorption processes, which require appropriate adsorption energies for different intermediates. Obviously, single-site catalysts cannot satisfy these demands, but multi-site electrocatalysts can offer multiple catalytic sites to separately interact with different intermediates and optimize adsorption strengths. Herein, we focus on multi-site electrocatalysts for the neutral HER, with the aim of offering an overview of novel design principles, progress, and perspectives in this area. To clearly reveal the important functions of multiple sites for the neutral HER, we first introduce the theoretical fundamentals of multi-site electrocatalysts for the HER in neutral media, then summarize a series of representative multi-site electrocatalysts, and systematically discuss these electrocatalysts from the theoretical calculation and experimental aspects. Finally, some challenges and further perspectives for the future development of multi-site electrocatalysts are presented. It is hoped that the review will provide valuable guidance for the rational design of multi-site water splitting electrocatalysts.