Intrinsic bimetallic cations regulating band centers and reactive sites for boosting CO2 photoreduction

Abstract

Artificial photosynthesis utilizing crucial photocatalysts to convert CO₂ into chemical fuels using solar energy shows huge potential. However, the efficiency is restricted by the weak reducibility of the catalyst and the chemical inertness of CO₂ molecules. The introduction of foreign metallic species is well recognized, while regulation of intrinsic metallic sites gains less attention. Herein, we unravel the atomic-level mechanism of intrinsic metallic cation regulation for promoting photocatalytic CO₂ reduction based on the model of bimetallic CdBiO₂Br with varied cation proportions. The introduction of Cd atoms leads to the formation of a favorable conduction band bottom dominated by Cd 5s with an orbital center of 0.79 eV, far more positive than that of Bi 6p (−0.29 eV) in BiOBr, accompanied by the greatly reduced work function from 4.42 eV to 2.73 eV. This not only largely elevates the reduction ability of electrons, but also opens up more possibilities for the transition of excited electrons from interfacial Cd atoms to adsorbed CO₂ on the catalyst surface. In particular, the reactive sites switch from Bi in BiOBr to O–Cd sites in CdBiO₂Br, which allows stronger chemisorption and easier activation of CO₂ molecules, benefiting the formation of the *COOH key intermediate with a low energy barrier and subsequent reactions to produce CO. Nonetheless, excessive Cd dilutes the CO₂ adsorption amount and charge separation. Thus, the well-optimized Cd_0.46Bi_1.36O₂Br shows an excellent CO yield of 36.3 μmol g⁻¹ with high selectivity. This work presents a feasible methodology to manipulate and design the catalytic sites on the basis of ontological cation constitution.