Ag-induced Phase Transition of Bi2O3 Nanofibers for Enhanced Energy Conversion Efficiency towards Formate in CO2 Electroreduction

Abstract

Bi-based electrocatalysts have been widely investigated in the CO2 reduction reaction (CO2RR) 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−Bi2O3 hybrid nanofiber (Ag−Bi2O3) for highly efficient electrochemical reduction of CO2 to formate. Ag−Bi2O3 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−Bi2O3 increased the EE (52.7%) by nearly 10% compared to a Bi2O3 only counterpart. Structural characterization and in-situ Raman results suggest that the presence of Ag induced the conversion of Bi2O3 from a monoclinic phase (α-Bi2O3) to a metastable tetragonal phase (β-Bi2O3) and accelerated the formation of active metallic Bi at low overpotentials (at > −0.3 V), which together contributes to the highly efficient formate formation.