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Xin Wang, Wenhui He, Jialin Shi, João Ricardo Coelho Junqueira, Jian Zhang, Stefan Dieckhöfer, Sabine Seisel, Debanjan Das, Wolfgang Schuhmann

• Bi-based electrocatalysts have been widely investigated in the CO\(_{2}\) reduction reaction (CO\(_{2}\)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−Bi\(_{2}\)O\(_{3}\) hybrid nanofiber (Ag−Bi\(_{2}\)O\(_{3}\)) for highly efficient electrochemical reduction of CO\(_{2}\) to formate. Ag−Bi\(_{2}\)O\(_{3}\) 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−Bi\(_{2}\)O\(_{3}\) increased the EE (52.7%) by nearly 10% compared to a Bi\(_{2}\)O\(_{3}\) only counterpart. Structural characterization and in-situ Raman results suggest that the presence of Ag induced the conversion of Bi\(_{2}\)O\(_{3}\) from a monoclinic phase (\(\alpha\)-Bi\(_{2}\)O\(_{3}\)) to a metastable tetragonal phase (\(\beta\)-Bi\(_{2}\)O\(_{3}\)) and accelerated the formation of active metallic Bi at low overpotentials (at > −0.3 V), which together contributes to the highly efficient formate formation.