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 V_RHE 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.