Reversible Aqueous Zinc–CO2 Batteries Based on CO2–HCOOH Interconversion

As a promising technique for CO2 fixation/utilization and energy conversion/storage, the metal–CO2 battery has been studied to improve its interconversion between CO2 and carbonates/oxalates. Herein, we propose and realize a reversible aqueous Zn–CO2 battery based on the reversible conversion between CO2 and liquid HCOOH on a bifunctional Pd cathode. The 3D porous Pd interconnected nanosheet with enriched edge and pore structure, has a highly electrochemical active surface to facilitate simultaneous selective CO2 reduction and HCOOH oxidation at low overpotentials. The resulting battery has a 1 V charge voltage, a cycling durability over 100 cycles, and a high energy efficiency of 81.2 %. The battery mechanism is proposed as Zn+CO2+2 H++2 OH−↔ ZnO+HCOOH+H2O, through which the reversible conversion between CO2 and liquid HCOOH was realized. Zn–CO2 battery: The first reversible aqueous Zn–CO2 battery is prepared using 3D porous Pd interconnected nanosheets as the cathode which bifunctionally electrocatalyzes CO2 reduction and HCOOH oxidation with high activity and selectivity at low overpotentials.