Effect of Thickness of Chromium Hydroxide Layer on Ag Cocatalyst Surface for Highly Selective Photocatalytic Conversion of CO₂ by H₂O

In this study, we developed a Ag–Cr core–shell-structured (Ag@Cr) cocatalyst that modified the surface of the Ga2O3 photocatalyst. Compared to results provided by modifications with Ag cocatalysts and M–Cr dual cocatalysts (M = Au, Cu, Pd, and Pt), this change significantly improved the formation rate of CO and selectivity toward CO evolution in the photocatalytic conversion of CO2 by the electron donor H2O. As a result of this modification, the Cr­(OH)3·xH2O shell changed to Cr­(OH)x(CO3)y during the photocatalytic conversion. Furthermore, the thickness of the Cr­(OH)3·xH2O shell was found to influence the photocatalytic performance. More specifically, Cr­(OH)3·xH2O shells that were too thick or too thin were not beneficial to the CO evolution and suppression of H2 evolution. Notably, the highest photocatalytic activity (525.3 μmol h–1), selectivity toward CO evolution (85.2%), and turnover number of CO to Ag (167) was achieved over 0.25 mol % (Ag@Cr)/Ga2O3. In addition to Ga2O3, the Ag@Cr cocatalyst modification strategy can also be applied to other photocatalyst materials such as NaTaO3, ZnGa2O4, and ZnGa2O4/Ga2O3 for the highly effective photocatalytic conversion of CO2 to CO when using H2O as an electron donor