Electronic-Brake-Enabled Generation and Stabilization of Dynamic Active Interfaces for CO2-to-Formate Electroreduction

Controlling the dynamic reconstruction of oxide-derived catalysts is critical for electrochemical CO 2 reduction because their active structures are often metastable under cathodic conditions. For SnO 2 -based catalysts, partial reduction generates reconstructed SnO 2 /Sn interfacial structures that favor formate production, whereas excessive reduction to metallic Sn destroys these interfaces and promotes hydrogen evolution. Here, we develop a dopant-regulated reconstruction strategy in which low-valence, high-electronegativity Bi acts as an electronic brake to modulate SnO 2 reduction kinetics. The optimized Bi0.2 catalyst delivers a formate Faradaic efficiency above 93% for more than 130 h at 250 mA cm −2 in a flow cell and maintains robust performance across diverse electrolyte environments. In situ and ex situ structural/electronic characterizations show that Bi incorporation mitigates deep SnO 2 reduction and helps preserve the reconstructed SnO 2 /Sn interface under cathodic operating conditions. In situ Raman spectroscopy and attenuated total reflection surface-enhanced infrared absorption spectroscopy measurements reveal potential-dependent changes in the interfacial water environment and support the involvement of activated CO 2 -related and * OCHO-related species in formate formation. Density functional theory calculations further show that Bi lowers the largest uphill Gibbs free-energy step for * OCHO formation while increasing that for the competing hydrogen evolution reaction pathway. These results establish dopant-regulated reconstruction and interfacial proton-coupled reaction regulation as design principles for sustainable CO 2 valorization.