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+H₂ O, through which the reversible conversion between CO₂ and liquid HCOOH was realized.