Dual-Anion Regulation for Reversible and Energetic Aqueous Zn-CO 2 Batteries.

Aqueous Zn-CO 2 batteries can not only convert CO 2 into high-value chemicals but also store/output electric energy for external use. However, their performance is limited by sluggish and complicated CO 2 electroreduction at the cathode. Herein, a dual-anion regulated Bi electrocatalyst is developed to selectively reduce CO 2 to formate with a Faradaic efficiency of up to 97% at a large current density of 250 mA cm -2 . With O and/or F, the rate-determine step of CO 2 electroreduction has been manipulated (from the first hydrogenation to *HCOOH desorption step) with a reduced energy barrier. Significantly, the fabricated Zn-CO 2 battery exhibits a high discharge voltage of 1.2 V, optimal power density of 4.51 mW cm -2 , remarkable energy density of 802 Wh kg -1 , and energy-conversion efficiency of 70.74%, stability up to 200 cycles and 68 h. This study provides possible strategies to fabricate reversible and energetic aqueous Zn-CO 2 batteries by addressing cathodic problems.