Bismuth Nanosheets Derived by In Situ Morphology Transformation of Bismuth Oxides for Selective Electrochemical CO₂ Reduction to Formate

Bismuth nanosheets (BiNSs) have been recognized as a promising catalyst for electrochemical CO2 reduction (CO2RR) to formate, but their preparation typically involves an elaborate synthesis of Bi precursors under elevated temperatures and pressures. Here, we demonstrate a simple surfactant-free method of preparing Bi2O3-derived BiNSs (OD-BiNSs) by aqueous precipitation and cyclic voltammetry (CV) under ambient conditions. In situ morphology transformation from Bi2O3 to BiNSs was observed during CV, in which the presence of oxygen and the initial morphology of Bi2O3 are crucial for the phase transformation. The as-prepared OD-BiNSs showed 93% of faradic efficiency (FE) to formate with a partial current density of 62 mA cm–2 at −0.95 VRHE in the H-cell and >94% FE at 50–200 mA cm–2 with cell voltages of 2.4–4.0 V in the flow cell.