Catalytically Active Site Identification of Molybdenum Disulfide as Gas Cathode in a Nonaqueous Li-CO₂ Battery

Li-CO₂ batteries have recently attracted attention as promising candidates for next-generation energy storage devices due to their extremely high theoretical energy density. The real application of Li-CO₂ cells involves addressing several drawbacks, including high charging potential, poor coulombic efficiency, and low rechargeability. Molybdenum disulfide supported on carbon nanotubes (MoS₂/CNT) with various ratios functioned as a cathode catalyst for Li-CO₂ batteries. The optimal MoS₂/CNT composite achieved a maximum discharge capacity of 8551 mAh g^-1 with a coulombic efficiency of 96.7%. This hybrid also obtained an initial charging plateau of 3.87 V at a current density of 100 mA g^-1 with a cutoff capacity of 500 mAh g^-1. It provided ideal electrochemical stability of 142 cycles at the current densities of 100 mA g^-1, which was comparable with that of some precious metal catalysts. This optimized MoS₂/CNT was also cycled at 200 and 400 mA g^-1 for 112 and 55 times, respectively. Density functional theory calculations demonstrated that the sulfided Mo-edge (s-Mo-edge) on MoS₂ materials showed appropriate adsorption strengths of Li, CO₂, and Li₂CO₃. Moreover, joint results of Raman profiles and extended X-ray absorption fine structure spectra elucidated that the catalytic efficiencies of MoS₂/CNT hybrids were proportional to the quantities of exposed s-Mo-edge active sites.