Photocatalytic and Photoelectrochemical Carbon Dioxide Reductions toward Value-Added Multicarbon Products

Developing new energy sources is of critical significance to satisfy the growing energy demand and also reduce the emissions of carbon dioxide (CO 2 ) gas. The conversion of CO 2 into value-added products is a promising strategy to achieve two aims at once, both mitigating the global warming issue and filling the huge gap between energy demand and sustainable supply. Photocatalytic (PC) and photoelectrochemical (PEC) CO 2 reduction reactions (CO 2 RRs), which utilize clean and renewable solar energy to access value-added products, are two strategies of great practical value. Multicarbon products have sparked great interest in recent years, owing to their higher energy densities and larger market sizes than C 1 species. However, the production of multicarbon products through PC and PEC CO 2 RRs is retarded by low activity and selectivity. In this work, the fundamentals of PC and PEC CO 2 RRs are first briefly recalled. Then, the main strategies toward high CO 2 RR activity and selectivity for multicarbon products (C 2 and C 3 species, instead of C 1 species, as major products or even the only product) are discussed, from the points of photocatalysts, electrons, and protons sources, applied bias, and reaction configuration. Finally, perspectives for future challenges and directions are presented.