Operando nuclear magnetic resonance decodes alkali-tuned proton-electron relay boosting CO2-to-formate conversion

The proton-coupled electron transfer (PCET) kinetics plays a critical role in governing the CO2-to-formate conversion efficiency during CO2 eletroreduction reaction. While alkali metal cations are known to influence the reaction pathway, elucidating how trace doping modifies the catalytic sites remains a key challenge. Here we show that incorporating Li into bismuth oxycarbonate (BOC-Li) induces structural modifications that optimize the PCET process at bismuth-active sites, thereby boosting CO2-to-formate conversion. By employing dual-isotope (2H/13C) operando nuclear magnetic resonance (NMR) to track the formation of 1H13COO−/2H13COO−, combined with kinetic isotope effect, Tafel analysis and in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy, we observe a more efficient proton-electron transfer pathway. Density functional theory (DFT) calculations suggest that Li doping is associated with enhanced activity of Bi sites, potentially strengthening H2O/CO2 adsorption and reducing the O–H activation energy. Collectively, this work highlights alkali doping as a promising strategy for structurally engineering catalytic sites to improve PCET kinetics. Understanding how alkali doping promotes CO2 electroreduction is challenging, as tracking proton transfer is difficult. Here, the authors report operando nuclear magnetic resonance spectroscopy reveals Li doping promotes a proton–electron relay from water, thereby boosting CO2-to-formate conversion.