Promoting Electrocatalytic CO2 Reduction to CO via Sulfur-Doped Co-N-C Single-Atom Catalyst

Electrocatalytic reduction of CO2 to fuels and chemicals possesses huge potential to alleviate current environmental crisis. Heteroatom doping in metal-nitrogen-carbon (M-N-C) single-atom catalysts (SACs) has been found to be capable to promote the electrocatalytic CO2 reduction reaction (CO2RR). However, the origin of the enhanced activity is still elusive. Here, we report that sulfur-doped cobalt-nitrogen-carbon single-atom catalyst (Co1-SNC) exhibits superior CO2RR performance compared to sulfur-free counterpart (Co1-NC). On the basis of in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), kinetic isotope effect (KIE) and theoretical calculation, it is demonstrated that sulfur doping can promote water activation, elevate the d-band center of Co active site, and reduce the free energy of *COOH intermediate formation. This work deepens the understanding of the CO2RR chemistry over heteroatom-doped SACs for designing efficient CO2RR processes.