Toward unlocking the potential of aqueous Zn-CO₂ batteries: What factors affect the electrochemical performance?

Aqueous rechargeable Zn-CO₂ batteries (ARZCBs) have garnered significant attention due to their dual potential for energy storage and the conversion of CO₂ into high-value chemicals or fuels. Despite recent advancements in preliminary validation of ARZCBs feasibility, considerable debate persists regarding the parameters influencing their electrochemical performances. In this study, we fabricated ARZCBs based on a flow-type configuration using coralloid Au catalyst and systematically evaluated their electrochemical performances by exploring electrolyte composition, gas environment, and device design, while analyzing the effect of these factors on battery performance. The results reveal that optimizing the electrolyte combination (catholyte: 2 M KHCO₃/6 M KOH, anolyte: 0.2 M Zn(OAc)₂) significantly enhances the electrochemical performance of H-type ARZCBs. Furthermore, the implementation of a flow-cell configuration, featured with a gas diffusion electrode, reduced electrode spacing and a bipolar membrane, effectively mitigates CO₂ mass transfer limitations and reduces cell impedance, resulting in substantial improvements in power density, and cycling stability. Therefore, our ARZCBs achieve a maximum power density of 5.04 mW cm⁻². The voltage gap remains stable after 80 cycles, demonstrating excellent cycling stability and reversibility. Additionally, a high CO Faradaic efficiency of up to 86.8 % is achieved at 5 mA cm⁻², further validating the effectiveness of our optimization strategies in enhancing ARZCBs performance. The strategies in this work provide valuable insights for the design of next-generation ARZCBs and highlight their application potential in efficient CO₂ conversion technologies.