Trace Sulfur Pre-Doped Bismuth Electrocatalysts for Stable and Efficient CO2 Reduction to Formate
Electrocatalytic CO2 reduction reaction (CO2RR) to formate offers a promising pathway for storing renewable electricity in chemical fuels and enabling carbon recycling. The development of efficient and stable catalysts for this specific pathway, however, remains a central challenge. Heteroatom doping can significantly tune the interaction between active sites and key intermediates, boosting catalytic performance. Conventional doping in Bi-based catalysts often relies on uncontrollable in-situ electrochemical processes, leading to ineffective bulk incorporation. Here, we present a simple pre-doping strategy that enables precise doping at surface active sites, thereby enhancing electrochemical performance. The resulting catalyst achieves >95% Faradaic efficiency for formate across 100–500 mA cm−2 in a flow cell and maintains >95% efficiency for over 70 h at 100 mA cm−2 in a membrane electrode assembly, outperforming pure Bi and Bi2S3. A solar-driven system further demonstrates a 4.4% solar-to-formate conversion efficiency. Mechanistic studies reveal that sulfur doping increases electron density, stabilizes the key *OCHO intermediate, and suppresses hydrogen evolution. These findings provide valuable insights into the precise pre-doping modulation of surface active sites for designing highly efficient and stable CO2RR catalysts.