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

Metal-CO₂ rechargeable batteries are of great importance due to their higher energy density and carbon capture capability. In particular, Na-CO₂ 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-CO₂ battery increases because of the cathode catalyst's inability to break down the insulating discharge product Na₂CO₃, thereby resulting in poor cycle performance. Herein, we develop an ultrathin nanosheet MoS₂/SnS₂ cathode composite catalyst for Na-CO₂ battery application. Insertion of SnS₂ reduces the overpotential and improves the cyclic stability compared to pristine MoS₂. 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 Na₂CO₃. Furthermore, the battery with the MoS₂/SnS₂ cathode catalyst has a discharge capacity of 35 889 mAh/g. The reasons for improvements in the cycle performance and overpotential of the MoS₂/SnS₂ 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. SnS₂ incorporation induces S-vacancies in the basal plane and 1T character in 2H MoS₂. This combined impact of SnS₂ incorporation results in undercoordinated Mo atoms. Such a change in the electronic structure and the phase of the MoS₂/SnS₂ composite cathode catalyst results in higher catalytic activity and reduces the cell overpotential.