Stabilizing Lattice Oxygen of Bi₂O₃ by Interstitial Insertion of Indium for Efficient Formic Acid Electrosynthesis

Bismuth oxide (Bi₂O₃) emerges as a potent catalyst for converting CO₂ to formic acid (HCOOH), leveraging its abundant lattice oxygen and the high activity of its Bi-O bonds. Yet, its durability is usually impeded by the loss of lattice oxygen causing structure alteration and destabilized active bonds. Herein, we report an innovative approach via the interstitial incorporation of indium (In) into the Bi₂O₃, significantly enhancing bond stability and preserving lattice oxygen. The optimized In-Bi₂O₃-100 catalyst achieves over 90 % Faradaic efficiency for HCOOH production across a wide potential range, in both H-cells and flow cells, maintaining robust stability after 100 hours of continuous operation. In situ surface-enhanced infrared absorption spectroscopy and theoretical calculations reveal that the interstitial In doping precisely tunes the adsorption of CO₂* and OCHO* intermediate, facilitating rapid conversion. Further in situ Raman spectroscopy confirms the role of In bolstering the oxidized structure's stability within Bi₂O₃, critical for sustaining lattice oxygen during electrochemical CO₂ reduction.