Upgrading Cycling Stability and Capability of Hybrid Na-CO2 Batteries via Tailoring Reaction Environment for Efficient Conversion CO2 to HCOOH

Rechargeable Na-CO 2 batteries are considered to be an effective way to address the energy crisis and greenhouse effect due to their dual functions of CO 2 fixation/utilization and energy storage. However, the insolubility and irreversibility of solid discharge products lead to poor discharge capacity and poor cycle performance. Herein, a novel strategy is proposed to enhance the electrochemical performance of hybrid Na-CO 2 batteries, using water-in-salt electrolyte (WiSE) to establish an optimal reaction environment, regulate the CO 2 reduction pathway, and ultimately convert the discharge product of the battery from Na 2 CO 3 to formic acid (HCOOH). This strategy effectively resolves the issue of poor reversibility, allowing the battery to exhibit excellent cycle performance (over 1200 cycles at 30 °C), especially under low-temperature conditions (2534 cycles at −20 °C). Furthermore, density functional theory (DFT) calculations and experiments indicate that by adjusting the relative concentration of H/O atoms at the electrolyte/catalyst interface, the CO 2 reduction pathway in the battery can be regulated, thus effectively enhancing CO 2 capture capability and consequently achieving an ultra-high discharge specific capacity of 148.1 mAh cm −2 . This work effectively promotes the practical application of hybrid Na-CO 2 batteries and shall provide a guidance for converting CO 2 into products with high-value-added chemicals.