High-performance Na–CO2 batteries with ZnCo2O4@CNT as the cathode catalyst

Abstract

Rechargeable Na–CO₂ batteries are promising energy storage devices as they not only provide high energy density but also utilize earth-abundant Na and the greenhouse gas CO₂. However, Na–CO₂ battery development is deterred due to the sluggish electrochemical reactions at the cathode. The cathode catalyst is unable to decompose the insulating discharge product Na₂CO₃, thereby leading to increasing charge overpotential and poor cycle performance of the Na–CO₂ battery. Herein, we report spinel ZnCo₂O₄ porous nanorods with multiwall carbon nanotubes (ZnCo₂O₄@CNT) as a cathode composite in the Na–CO₂ batteries to effectively decompose Na₂CO₃ and improve the cycle performance. The battery shows stable discharge–charge for at least 150 cycles with a limited capacity of 500 mA h g⁻¹ at 100 mA g⁻¹. Moreover, the battery with the ZnCo₂O₄@CNT cathode catalyst exhibits a reversible discharge–charge capacity of 12 475 mA h g⁻¹. Theoretical simulations suggest that the adsorption energies of CO₂, Na, and Na₂CO₃ on the three surfaces of ZnCo₂O₄ are favorable for the CO₂RR and CO₂ER during the charge–discharge of the Na–CO₂ battery. The surfaces of ZnCo₂O₄ investigated for catalytic activity include the [001] surface, the [111] surface with only exposed Co atoms, and the [111] surface with exposed Co and Zn atoms. The density of states calculation results further reveal that Co atoms on these three surfaces are possibly the catalytic active sites for the CO₂RR and CO₂ER during the charge–discharge of the Na–CO₂ battery.