Recent advances and perspectives in cobalt-based heterogeneous catalysts for photocatalytic water splitting, CO2 reduction, and N2 fixation

Solar-driven conversion of carbon dioxide, water and nitrogen into high value-added fuels (e.g. H2, CO, CH4, CH3OH, NH3 and so on) is regarded as an environmental-friendly and ideal route for relieving the greenhouse gas effect and countering energy crisis, which is an attractive and challenging topic. Hence, various types of photocatalysts have been developed successively to meet the requirements of these photocatalysis. Among them, cobalt-based heterogeneous catalysts emerge as one of the most promising photocatalysts that open up alluring vistas in the field of solar-to-fuels conversion, which can effectively enhance photocatalytic efficiency by extending light absorption range, promoting charge separation, providing active sites, and lowering reaction barrier. In this review, we first present the working principles of cobalt-based heterogeneous catalysts for photocatalytic water splitting, CO2 reduction, and N2 fixation. Second, five efficient strategies including surface modification, morphology modulation, crystallinity controlling, crystal engineering and doping, are discussed for improving the photocatalytic performance with different types cobalt-based catalysts (cobalt nanoparticles and single atom, oxides, sulfides, phosphides, MOFs, COFs, LDHs, carbide, and nitrides). Third, we outline the applications for the state-of-the-art photocatalytic CO2 reduction and water splitting, and nitrogen fixation over cobalt-based heterogeneous catalysts. Finally, the central challenges and possible improvements of cobalt-based photocatalysis in the future are presented. The purpose of this review is to summarize the past experience and lessons, and provide reference for the further development of cobalt-based photocatalysis technology.