Structural Role of Different MXenes in CoMnS Composites for High-Energy Ionic Liquid Supercapacitors

Abstract A systematic comparative study of three MXenes, Ti3C2 (TC), V2C (VC), and Mo2Ti2C3 (MTC), and their corresponding CoMnS (CMS) composites was conducted to elucidate the influence of MXene chemistry on electrochemical performance. The composites were synthesized via in situ growth of CMS on MXene surfaces, promoting strong interfacial interactions and uniform dispersion of redox-active species. Structural characterization revealed that TC possesses the most ordered layered structure and highest synthesis efficiency, whereas MTC exhibits a more disordered morphology. Despite this, MTC-based composites delivered superior electrochemical performance owing to enhanced interfacial activity and faster ion/electron transport. All MXene/CMS composites significantly outperformed their pristine counterparts when employed as positive electrodes in asymmetric supercapacitors. A maximum energy density of 432.3 Wh kg–1 and a specific capacitance of 1216 F g–1 were achieved by the MTC/CMS device at 0.5 A g–1. The highest power density of 8000 W kg–1 was obtained from the MTC/CMS device at 5 A g–1 current density. In addition, a capacitance retention of ∼94% was observed after 10,000 continuous cycles in an ionic liquid electrolyte. These enhanced properties are credited to a mutual reinforcement between Co/Mn redox-active pseudocapacitance and MXene-derived electric double-layer capacitance. Overall, the electrochemical performance follows the order: MTC/CMS > VC/CMS > TC/CMS > MTC > VC > TC > CMS, highlighting the importance of MXene-dependent interfacial engineering for advanced energy-storage systems.