Regulating the *OCCHO intermediate pathway towards highly selective photocatalytic CO₂ reduction to CH₃CHO over locally crystallized carbon nitride

Photocatalytic conversion of CO₂ to CH₃CHO is of increasing interest but confronts the significant challenges of forming C–C bonds and keeping the CO bond intact throughout the process. Here, we report the selective photocatalytic hydrogenation of CO₂ to CH₃CHO using a modified polymeric carbon nitride (PCN) under mild conditions. The locally crystallized PCN offers a photocatalytic activity of 1814.7 μmol h⁻¹ g⁻¹ with a high selectivity of 98.3% for CH₃CHO production and a quantum efficiency of 22.4% at 385 nm, outperforming all the state-of-art CO₂ photocatalysts. The promoted formation of the *OCCHO intermediate on the locally crystallized PCN is disclosed as the key factor leading to the highly selective CH₃CHO generation. The locally crystallized PCN favors spontaneous C–C coupling towards *OCCHO formation rather than *CHO protonation, thus preventing HCHO formation. This work provides a new strategy for designing carbon nitrides for highly selective and sustainable conversion of CO₂ to CH₃CHO.