Phase‐Controlled Bi 2 O 3 Nanosheets for Highly Efficient Electrochemical CO 2 Reduction to Formate

Abstract

ABSTRACT The electrochemical carbon dioxide reduction reaction (CO 2 RR) offers a sustainable route to convert CO 2 into valuable chemicals, with formic acid being one of the most economically attractive products. Bismuth (Bi)‐based materials have shown promise as CO 2 RR electrocatalysts, yet their practical application is hindered by structural instability, competing side reactions, and the lack of a systematic understanding of phase‐dependent catalytic behavior. Herein, we report the synthesis of β‐Bi 2 O 3 , δ‐Bi 2 O 3 , and α‐Bi 2 O 3 with uniform 2D nanosheet morphologies, enabling a direct and fair comparison of their CO 2 RR performance. Notably, the β‐Bi 2 O 3 nanosheets (NSs), which have not been previously reported, deliver a formate faradaic efficiency of 99.0% at −0.8 V versus the reversible hydrogen electrode in 1.0 m KOH, along with a formate production rate of 3321 µmol cm −2 h −1 , surpassing most reported Bi‐based catalysts. Through comprehensive structural characterization and combined experimental and theoretical investigations covering CO 2 ‐to‐formate reduction, formate decomposition, and the hydrogen evolution reaction, we establish a clear phase‐activity relationship. This work not only demonstrates the performance of β‐Bi 2 O 3 NSs but also provides new insights into the rational design of phase‐engineered Bi‐based electrocatalysts for CO 2 RR.