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

Abstract

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 CO 2 reduction reaction. Here, we show that reversible Mo 5+ /Mo 6+ as a mediator can regulate the proton and electron transfer process at the Bi 2 MoO 6 nanosheet/In 2 O 3 microtube (BI) catalyst. The formed concerted proton-coupled electron transfer enables a champion solar-to-methane efficiency of 0.15%, resulting in nearly 100% CH 4 selectivity and a competitive CH 4 yield of 46.37 μmol g −1 h −1 in pure water. The experiments, together with theoretical calculations, clearly validate that In sites as H 2 O 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 CO 2 adsorption/reduction centers, thus achieving precise hydrogenation on Bi sites for binding of the *CH 3 O key intermediate to form CH 4 .