Perovskite‐Derived Bismuth with I⁻ and Cs⁺ Dual Modification for High‐Efficiency CO₂‐to‐Formate Electrosynthesis and Al‐CO₂ Batteries

Abstract Bi‐based materials are one of the most promising candidates for electrochemical CO₂ reduction reaction (CO₂RR) to formate; however, the majority of them still suffer from low current density and stability that essentially constrain their potential applications at the industrial scale. Surface modification represents an effective approach to modulate the electrode microenvironment and the relative binding strength of key intermediates. Herein, it is demonstrated that the surface comodification with halides and alkali metal ions from the conversion of Bi‐based halide perovskite nanocrystals is a viable strategy to boost the CO₂RR performance of Bi for formate electrosynthesis. Cs₃Bi₂I₉ nanocrystals are prepared by a hot‐injection method. The as‐prepared products feature well‐defined hexagonal shape and uniform size distribution. When used as the precatalyst, Cs₃Bi₂I₉ nanocrystals are converted to Cs⁺ and I⁻ comodified Bi. The resultant catalyst exhibits high formate Faradaic efficiency close to 100%, and remarkable partial current density up to 44 mA cm⁻² in an H‐cell and up to 276 mA cm⁻² in a flow cell. Moreover, Cs₃Bi₂I₉ is used as the cathode catalyst and paired with an Al anode in an Al‐CO₂ battery for simultaneous CO₂ valorization and power generation.