Ag-induced Phase Transition of Bi₂ O₃ Nanofibers for Enhanced Energy Conversion Efficiency towards Formate in CO₂ Electroreduction

Bi-based electrocatalysts have been widely investigated in the CO₂ reduction reaction (CO₂ RR) for the formation of formate. However, it remains a challenge to achieve high Faradaic efficiency (FE) and industrial current densities at low overpotentials for obtaining both high formate productivity and energy efficiency (EE). Herein, we report an Ag-Bi₂ O₃ hybrid nanofiber (Ag-Bi₂ O₃ ) for highly efficient electrochemical reduction of CO₂ to formate. Ag-Bi₂ O₃ exhibits a formate FE of >90% for current densities from -10 to -250 mA ⋅ cm^-2 and attains a yield rate of 11.7 mmol ⋅ s^-1 ⋅ m^-2 at -250 mA ⋅ cm^-2 . Moreover, Ag-Bi₂ O₃ increased the EE (52.7%) by nearly 10% compared to a Bi₂ O₃ only counterpart. Structural characterization and in-situ Raman results suggest that the presence of Ag induced the conversion of Bi₂ O₃ from a monoclinic phase (α-Bi₂ O₃ ) to a metastable tetragonal phase (β-Bi₂ O₃ ) and accelerated the formation of active metallic Bi at low overpotentials (at > -0.3 V), which together contributes to the highly efficient formate formation.