Molybdenum Disulfide/Tin Disulfide Ultrathin Nanosheets as Cathodes for Sodium-Carbon Dioxide Batteries.

Metal-CO rechargeable batteries are of great importance due to their higher energy density and carbon capture capability. In particular, Na-CO batteries are potential energy-storage devices that can replace Li-based batteries due to their lower cost and abundance. However, because of the slow electrochemical processes owing to the carbonated discharge products, the cell shows a high overpotential. The charge overpotential of the Na-CO battery increases because of the cathode catalyst's inability to break down the insulating discharge product NaCO, thereby resulting in poor cycle performance. Herein, we develop an ultrathin nanosheet MoS/SnS cathode composite catalyst for Na-CO battery application. Insertion of SnS reduces the overpotential and improves the cyclic stability compared to pristine MoS. As shown by a cycle test with a restricted capacity of 500 mAh/g at 50 mA/g, the battery is stable up to 100 discharge-charge cycles as the prepared catalyst successfully decomposes NaCO. Furthermore, the battery with the MoS/SnS cathode catalyst has a discharge capacity of 35 889 mAh/g. The reasons for improvements in the cycle performance and overpotential of the MoS/SnS composite cathode catalyst are examined by a combination of Raman, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure analysis, which reveals an underneath phase transformation and changes in the local atomic environment to be responsible. SnS incorporation induces S-vacancies in the basal plane and 1T character in 2H MoS. This combined impact of SnS incorporation results in undercoordinated Mo atoms. Such a change in the electronic structure and the phase of the MoS/SnS composite cathode catalyst results in higher catalytic activity and reduces the cell overpotential.