Concerted Proton-Coupled Electron Transfer by Mo5+/Mo6+ Reversible Transformation for CO2 Photoreduction with Nearly 100% CH4 Selectivity

Regulation of the proton-coupled electron transfer (PCET) process to avoid the unbalanced proton and electron regions on the reduction active sites is key to dictating product selectivity in a photocatalytic CO₂ reduction reaction. Here, we show that reversible Mo⁵⁺/Mo⁶⁺ as a mediator can regulate the proton and electron transfer process at the Bi₂MoO₆ nanosheet/In₂O₃ microtube (BI) catalyst. The formed concerted proton-coupled electron transfer enables a champion solar-to-methane efficiency of 0.15%, resulting in nearly 100% CH₄ selectivity and a competitive CH₄ yield of 46.37 μmol g^–1 h^–1 in pure water. The experiments, together with theoretical calculations, clearly validate that In sites as H₂O oxidation centers provide protons, and the regulation of protons and electrons by using Mo sites forms approximate electroneutral proton/electron pairs, which are conjointly transferred to Bi sites as CO₂ adsorption/reduction centers, thus achieving precise hydrogenation on Bi sites for binding of the *CH₃O key intermediate to form CH₄.