Triphase Photocatalytic CO₂ Reduction over Silver‐Decorated Titanium Oxide at a Gas–Water Boundary

Photocatalytic CO 2 reduction reaction (CO 2 RR) is an attractive process to convert CO 2 into valuable chemicals. But this reaction is often restricted by the poor mass transfer of CO 2 in the liquid phase. Here, we have developed a triphase photocatalytic CO 2 RR system by supporting Ag‐decorated TiO 2 nanoparticles at a gas–water boundary with hydrophobic–hydrophilic abrupt interfacial wettability. Such a triphase system allows the rapid delivery of gas‐phase CO 2 to the surface of photocatalysts while maintaining an efficient water supply and uncovered active sites. Ag‐TiO 2 supported at the gas–water boundary showed a CO 2 reduction rate of 305.7 μmol g −1 h −1 , without hole scavengers, approximately 8 times higher than the nanoparticles dispersed in the liquid phase. Even using diluted CO 2 (10 %) as the reactant, the CO 2 RR activity was superior to most reported Ag‐TiO 2 based photocatalysts using pure CO 2 . The findings provide a general strategy to promote the interfacial CO 2 mass transfer to improve photoactivity and selectivity.