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

As a promising technique for CO 2 fixation/utilization and energy conversion/storage, the metal–CO 2 battery has been studied to improve its interconversion between CO 2 and carbonates/oxalates. Herein, we propose and realize a reversible aqueous Zn–CO 2 battery based on the reversible conversion between CO 2 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 CO 2 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+CO 2 +2 H + +2 OH − ↔ ZnO+HCOOH+H 2 O, through which the reversible conversion between CO 2 and liquid HCOOH was realized.