Electronegativity drives charge polarization in indium single-atom catalysts for low-overpotential CO₂ electroreduction

Electrochemical CO₂ reduction to formate is limited by high overpotentials and competing reactions. Herein, we report an indium single-atom catalyst that modulates the adsorption geometry of CO₂ by engineering the charge state of the active site. The optimized catalyst achieves a Faradaic efficiency (FE) for formate of 93.5% at −0.6 V vs. RHE in a flow cell with 400 mV overpotential and maintains high selectivity across a wide potential window (-0.6 to −0.9 V). The overpotential of formate is highly sensitive to the initial dispersion of In atoms causing optimal CO₂ adsorption and fast electron transfer, and increases significantly when In clusters/particles become predominant species. In situ characterizations and theoretical calculations indicate that oxygen-coordinated isolated In sites induce significant interfacial charge polarization, which preferentially stabilizes a bidentate O-bound adsorption configuration of CO₂-derived intermediates through strong In-O interactions and thereby enables highly selective conversion to formate. This work identifies electronegativity as a key descriptor for controlling intermediate adsorption on p-block single-atom catalysts and provides insights into the rational design of selective CO₂RR electrocatalysts.