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

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.