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

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.