Unpaired Electron Engineering Enables Efficient and Selective Photocatalytic CO2 Reduction to CH4.

Abstract

The photocatalytic CO2 reduction to CH4 reaction is a long process of proton-coupled charge transfer accompanied by various reaction intermediates. Achieving high CH4 selectivity with satisfactory conversion efficiency therefore remains rather challenging. Herein, we propose a novel strategy of unpaired electron engineering to break through such a demanding bottleneck. By taking TiO2 as a photocatalyst prototype, we prove that unpaired electrons stabilize the key intermediate of CH4 production, i.e., CHO*, via chemical bonding, which converts the endothermic step of CHO* formation to an exothermic process, thereby altering the reaction pathway to selectively produce CH4. Meanwhile, these unpaired electrons generate midgap states to restrict charge recombination by trapping free electrons. As an outcome, such an unpaired electron-engineered TiO2 achieves an electron-consumption rate as high as 28.3 μmol·g-1·h-1 (15.7-fold with respect to normal TiO2) with a 97% CH4 selectivity. This work demonstrates that electron regulation holds great promise in attaining efficient and selective heterogeneous photocatalytic conversion.