Sb-Doped Bi₂O₃ Nanosheets for Selective Electroreduction of CO₂ to Formic Acid

Electrochemical carbon dioxide reduction reaction (CO2RR) into value-added chemicals offers a promising pathway to mitigate climate change and promote sustainable energy conversion. In this work, we synthesize antimony (Sb)-doped bismuth oxide (Bi2O3) nanosheets (NSs) as highly efficient and selective electrocatalysts for the CO2RR to formic acid. Incorporating Sb into Bi2O3 effectively modulates the local electronic environment of Bi atoms, creating electron-deficient sites. These sites significantly enhance CO2 adsorption and stabilize the key intermediate (*OCHO), verified by in situ Raman spectroscopy, where the Sb-doped Bi2O3 NSs exhibited the early onset and stronger intensity of the *OCHO vibrational signature compared to undoped Bi2O3. Among the various Sb doping levels, 10% Sb-doped Bi2O3 NSs exhibit the highest CO2RR performance, achieving a maximum Faradaic efficiency (FEHCOO–) of 88.2% at −1.5 V (vs RHE) and a partial current density (jHCOO–) of 80.1 mA·cm–2 at −1.7 V (vs RHE) in an H-type cell. Moreover, in a solid-state electrolyte (SSE) cell for electrolyte-free formic acid (HCOOH) production, the Sb-doped Bi2O3 NSs show an excellent partial current density (jHCOOH) of 279.8 mA·cm–2 for HCOOH production. Notably, the direct formation of highly concentrated formic acid (>10 wt %) is achieved as a single-pass product. Furthermore, the catalyst demonstrates robust stability, maintaining consistent performance over 24 h of operation. This study demonstrates Sb doping as an effective strategy for enhancing the electrocatalytic performance of Bi2O3-based electrocatalysts.