High-performance Na-CO₂batteries with ZnCo₂O₄@CNT as the cathode catalyst

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.