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.