Advanced noble-metal/transition-metal/metal-free electrocatalysts for hydrogen evolution reaction in water-electrolysis for hydrogen production

Hydrogen energy serves as an ideal alternative energy carrier to fossil fuels in the future clean energy system. The hydrogen evolution reaction (HER) occurring at the cathode of water electrocatalysis has been considered as a promising approach to produce hydrogen over the past decades due to zero carbon emission. To gain a deep insight into the advanced electrocatalyst, herein, we provide a comprehensive review with an emphasis on the recent state-of-the-art advances of HER electrocatalysts in view of controlling their local electronic structure, creating defect nanostructures, exposing active sites, altering d band center, and constructing heterogeneous structure. Initially, we start with a brief introduction of the fundamental electrocatalytic mechanisms and the critical electrochemical parameters for evaluating HER. Then, we systemically discuss three representative classes of electrocatalysts, comprised of highly active noble-metal including single atom, nanoparticles, and clusters, earth-abundant transition metal such as transition metal sulfides, phosphides, carbides, nitrides, and oxides, and metal-free functional nanomaterials involving different dimensions of carbonaceous nanomaterials, boron nitrogen, and phosphorous non-carbonaceous nanomaterials by adjusting their tunable electronic structures and architectures/morphologies with a particular emphasis on the structure–function relationships. Finally, we point out the current challenges and opportunities in view of achieving highly active and stable electrocatalysts towards practical applications.