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 CO 2 -to-formate conversion efficiency during CO 2 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 CO 2 -to-formate conversion. By employing dual-isotope ( 2 H/ 13 C) operando nuclear magnetic resonance (NMR) to track the formation of 1 H 13 COO − / 2 H 13 COO − , 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 H 2 O/CO 2 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.