Restructuring‐Regulated Bismuth Catalyst Promotes Electrochemical CO 2 Reduction to Formic Acid in Acidic Electrolyte

Electrochemical CO 2 reduction (eCO 2 R) in acidic electrolytes is appealing due to its high CO 2 utilization efficiency. For this reaction, bismuth (Bi)‐based catalysts have drawn considerable attention for their potential in producing formate/formic acid. However, the presynthesized materials for Bi‐based catalysts often undergo restructuring during electrocatalysis, resulting in altered electrochemical performance. Furthermore, the mechanisms underlying the restructuring of Bi‐based catalysts in acidic environments have not yet been clearly elucidated. Herein, distinct restructuring mechanisms are revealed in structurally different Bi‐based compounds, such as Bi 9 O 7.5 S 6 and Bi 2 O 2 S. Among them, the Bi 9 O 7.5 S 6 precatalyst exhibits high selectivity and activity for formic acid production, attributed to its unique structure, featuring stacking of [Bi 2 O 2 ] 2+ and [BiS 2 ] − layers. In contrast, the conventional Bi 2 O 2 S catalyst, characterized by alternating [Bi 2 O 2 ] 2+ layers with S 2− ions, delivers inferior eCO 2 R performances. Quasi‐in situ X‐ray diffraction and in situ Raman spectra results reveal that metal elements situated between two [Bi 2 O 2 ] 2+ layers can resist decomposition and prevent the over‐reduction of catalysts, leading to the restructuring in Bi/Bi 2 O 2 CO 3 composite material with active Bi‐Bi 2 O 2 CO 3 interface for formic acid production. As a result, the Bi 9 O 7.5 S 6 precatalyst achieves a high Faraday efficiency above 95% at 100 mA cm −2 and remarkable stability of 117 h in a flow cell.