Carbon-Encapsulated Electrocatalysts for the Hydrogen Evolution Reaction

Water electrolysis is a promising approach for large-scale and sustainable hydrogen production; however, its kinetics is slow and requires precious metal electrocatalysts to efficiently operate. Therefore, great efforts are being undertaken to design and prepare low-cost and highly efficient electrocatalysts to boost the hydrogen evolution reaction (HER). This is because traditional transition-metal electrocatalysts and corresponding hybrids with nonmetal atoms rely mainly on the interaction of metal-H bonds for the HER, which inevitably suffers from corrosion in extreme acidic and alkaline solutions. And as a result of all this effort, novel nanostructured electrocatalysts, such as carbon-encapsulated precious metals and non-precious metals including single metals or their alloys, transition-metal carbides, phosphides, oxides, sulfides, and selenides have all been recently reported to exhibit good catalytic activities and stabilities for hydrogen evolution. Here, the catalytic activity is thought to originate from the electron penetration effect of the inner metals to the surface carbon, which can alter the Gibbs free energy of hydrogen adsorption on the surface of materials. In this review, recent progresses of carbon-encapsulated materials for the HER are summarized, with a focus on the unique effects of carbon shells. In addition, perspectives on the future development of carbon-coated electrocatalysts for the HER are provided.