The introduction of heteroatoms (such as B, P, S and Se) into M-N-C catalysts provides a useful strategy to further enhance its catalytic activity due to the optimized electronic structure[11-14]. For example, Yang et al. developed S doped NiNC catalyst for robust CO2RR due to the formation of low-valent Ni(I)[15]. Besides, P doped FeNC catalyst also exhibited impressive performance owing to the moderate adsorption energy[16]. According to the previous reports, the formation of *COOH intermediate via the proton-electron transfer process is the rate-determining step (RDS) for CO2RR to CO[17, 18]. However, few studies have scrutinized the water activation and proton transfer.
In this work, we develop a Co1-SNC catalyst with S doped in the first shell of CoN4. The Co1-SNC exhibits superior CO2RR performance compared to Co1-NC. In situ ATR-SEIRAS and KIE studies indicate that Co1-SNC owns better water affinity and superior capability for water activation. Theoretical analyses further show that S doping can upshift the d-band center of Co active site and reduce the free energy of *COOH intermediate formation. This work enriches the understanding of CO2RR chemistry over heteroatom doping M-N-C SACs and offers new insights for developing high-performance catalysts for various important electrochemical reactions.
Results and Discussion