Sulfur Tailoring the d-Band Center of Cu Single Atoms via Engineering the Second Scattering Shell for Photocatalytic CO2 Reduction

Abstract Modulating the d-band center of metal emerges as an efficient strategy to boost photocatalytic CO2 reduction reaction (CO2RR). However, simple methods for accurate Cu d-band center control are lacking. Herein, a sulfur doping strategy was developed to precisely tailor the d-band center of a Cu single atom via the second scattering shell engineering. The prepared CuCN–S catalyst coupled with BiOBr exhibits superior photocatalytic performance of CO2 reduction to CO and delivers a CO evolution rate of 95.8 μmol g–1 h–1 with a 98% selectivity in pure water. Experimental and theoretical results confirm that S doping enhances light harvesting and charge separation in Cu SACs. Importantly, S doping in the second shell of the Cu site can effectively upshift Cu toward the Fermi level and simultaneously strengthens the metal–support interaction. The optimized electronic structure of Cu enhances the adsorption of CO2 and key *COOH intermediates, thereby lowering the energy barrier of the reaction. CuCN–S/BiOBr complex further promotes charge separation by the built-in electric field, strengthens the reaction kinetics at the oxidation reaction, and thereby further enhances the reaction activity. This work offers an insightful modulation strategy of the electronic structure for designing high-efficiency CO2RR photocatalysts.