Seven-coordinated BiO₇ motif as critical active site in oxidized bismuth for CO₂ electroreduction to formate

The BiO bond is widely regarded as the key motif for CO₂ electroreduction towards formate, but the role of specific BiO coordination remains unclear. Herein, we study the electrocatalytic behavior of a Bi₄Ti₃O₁₂ perovskite containing BiO₆ and BiO₇ structures. Under 24-h CO₂ reduction reaction (CO₂RR), Bi₄Ti₃O₁₂ reconstructs into Bi₂O₂CO₃ while retaining BiO₇ and maintaining high formate Faradaic efficiency (FE). In contrast, electrochemical measurements and in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) confirm Bi₂O₃ lacking BiO₇ favors hydrogen evolution reaction (HER). Density functional theory (DFT) calculations indicate BiO₇ lowers the energy barrier for *OCHO generation, identifying it as the key active site. Using a solid-state electrolyte (SSE) reactor, pure formic acid (0.19 M) is continuously produced with ∼70% FE over 48 h. This work indicates that the coordination environment of BiO motif displays an essential role in selectivity, and that the BiO₇ motif might be the critical active site for formate production.