Unpaired Electron Engineering Enables Efficient and Selective Photocatalytic CO 2 Reduction to CH 4 .

The photocatalytic CO 2 reduction to CH 4 reaction is a long process of proton-coupled charge transfer accompanied by various reaction intermediates. Achieving high CH 4 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 TiO 2 as a photocatalyst prototype, we prove that unpaired electrons stabilize the key intermediate of CH 4 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 CH 4 . Meanwhile, these unpaired electrons generate midgap states to restrict charge recombination by trapping free electrons. As an outcome, such an unpaired electron-engineered TiO 2 achieves an electron-consumption rate as high as 28.3 μmol·g -1 ·h -1 (15.7-fold with respect to normal TiO 2 ) with a 97% CH 4 selectivity. This work demonstrates that electron regulation holds great promise in attaining efficient and selective heterogeneous photocatalytic conversion.