Rational design of Ti₃C₂/carbon nanotubes/MnCo₂S₄ electrodes for symmetric supercapacitors with high energy storage

The enhancement of electrochemical performance of supercapacitors with high-energy storage is largely determined by the selective electrode materials and their rational structural design. In this paper, we fabricated Ti₃C₂/CNTs/MnCo₂S₄ composite electrodes by electrostatic self-assembly between positively charged multiwalled carbon nanotubes (CNTs) and negatively charged Ti₃C₂, followed by subsequent anchoring of bimetallic sulphide MnCo₂S₄ nanoparticles to Ti₃C₂/CNTs hybrid via a two-step hydrothermal method. All the Ti₃C₂/CNTs/MnCo₂S₄ composite electrodes exhibit enhanced specific capacitance comparing with the pure Ti₃C₂ electrodes. The optimized Ti₃C₂/CNTs/MnCo₂S₄ electrode shows paramount gravimetric capacitance (C_s) (823 F/g at a current density of 1A/g), high rate retention (63.5% of specific capacitance retains when current density increases from 1 to 5A/g), and excellent cycling stability (94.09% after 5000 charging and discharging cycles). These improved electrochemical performances are mainly attributed to the synergistic effect of high specific capacitance from the pseudocapative material of MnCo₂S₄, remarkable conductivity of Ti₃C₂ and CNTs, and the micro-/nano-porous structures constructed by stacking Ti₃C₂ flakes with CNTs. Moreover, the as-synthesized Ti₃C₂/CNTs/MnCo₂S₄ electrode-based symmetric supercapacitor demonstrates a high energy density of 49.5 Wh/kg at a power density of 350 W/kg, suggesting that the electrochemical performance of Ti₃C₂-based supercapacitors can be substantially boosted by rational design and modification of Ti₃C₂ electrodes with MnCo₂S₄ and multilayer CNTs.