Carbon dioxide photoreduction using a photocatalyst with prolonged charge-separated states and excess electron reservoirs

A persistent challenge in operating S-scheme photocatalysts involves maintaining complete neutralization of low-energy electrons and holes between reducing and oxidizing photocatalysts. To address this, we propose a charge replenishment-assisted S-scheme mechanism that combines a compatible host catalyst with a luminescence phosphor semiconductor capable of long-term storage of photogenerated electrons. Stored electrons can replenish the host photocatalyst, depleting the low-oxidizing holes, thus prolonging the charge-separated state. The concept is demonstrated in a core-shell-structured SrGa₂O₄:Cu²⁺/g-C₃N₄ (SGO/CN) photocatalyst, where stored electrons with a lifetime of up to several hours can continuously consume holes in the CN. The well-defined core-shell structure, abundant interfacial Sr-N bonds, and staggered band alignment between SGO and CN are crucial for this S-scheme interfacial charge transfer, which contributes to the enhanced CO₂-to-CO transformation activity and selectivity. This S-scheme heterojunction, incorporating a charge-storing material as an excess electron reservoir, offers a promising template for designing efficient photocatalytic systems.