Recent Advances in Cu-Based Cocatalysts toward Solar-to-Hydrogen Evolution: Categories and Roles

Solar-to-hydrogen production is one of the most promising solutions for global energy shortages and the environmental crisis because it utilizes solar energy to the fullest extent. Photocatalytically splitting water to hydrogen involves three crucial processes: solar light harvesting, charge separation/migration, and the catalytic H-2 production reaction. In the past few years, much attention is paid to investigating noble metal cocatalysts for solar photoreduction, but much less attention is paid to transition metal-based cocatalysts. Nevertheless, great and significant advances are achieved using a copper-based cocatalyst for solar-to-hydrogen evolution, as it possesses a suitable binding energy for the hydrogen intermediate according to density functional theory calculations. This review summarizes recent studies and progress on the copper-based cocatalytic materials as well as discusses the roles and functional mechanisms for photocatalytic H-2 evolution. It begins with discussing basic principles for the use of cocatalysts for photocatalytic hydrogen evolution and points out opportunities to use non-noble metal cocatalysts for hydrogen evolution. Then, it explains the construction and structural features of a photocatalysis system with semiconductor-Cu-based cocatalyst, and how the functional mechanisms work to enhance the hydrogen-production-related reactions. Finally, some challenges and perspectives are also given to promote further exploration of this emerging research area.