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

Electrochemical carbon dioxide reduction reaction (CO 2 RR) 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 (Bi 2 O 3 ) nanosheets (NSs) as highly efficient and selective electrocatalysts for the CO 2 RR to formic acid. Incorporating Sb into Bi 2 O 3 effectively modulates the local electronic environment of Bi atoms, creating electron-deficient sites. These sites significantly enhance CO 2 adsorption and stabilize the key intermediate (*OCHO), verified by in situ Raman spectroscopy, where the Sb-doped Bi 2 O 3 NSs exhibited the early onset and stronger intensity of the *OCHO vibrational signature compared to undoped Bi 2 O 3 . Among the various Sb doping levels, 10% Sb-doped Bi 2 O 3 NSs exhibit the highest CO 2 RR performance, achieving a maximum Faradaic efficiency (FE HCOO – ) of 88.2% at −1.5 V (vs RHE) and a partial current density ( j HCOO – ) 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 Bi 2 O 3 NSs show an excellent partial current density ( j HCOOH ) 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 Bi 2 O 3 -based electrocatalysts.