2D Heterolayer-Structured MoSe₂-Carbon with Fast Kinetics for Sodium-Ion Capacitors

Two-dimensional (2D) layered MoSe₂ has been demonstrated to be a promising electrode material for new energy storage systems. However, its nature of poor conductivity and the undesirable interlayer spacing hinder its further application. In this paper, a general and simple plasma-enhanced chemical vapor deposition method is proposed to produce 2D heterolayer-structured MoSe₂-carbon (MoSe₂/C) with carbon atoms inserted in the MoSe₂ layers. After morphology optimization, when applying flat-type MoSe₂/C-200 nanosheets with an enlarged interlayer spacing of 0.79 nm as the anode and activated carbon as the cathode, the assembled sodium-ion hybrid capacitors can reach a maximum energy/power density of 116.5 W h kg^-1/107.5 W kg^-1 and exhibit superior cycling durability (91.3% capacitance retention after 4000 cycles at 1 A g^-1). The good electrochemical property can be ascribed to the enlarged interlayer spacing that can offer fast diffusion channels for Na ions, and the carbon layer sandwiched in the MoSe₂ layer can not only enhance the electron transfer, accelerating the reaction kinetics, but also alleviate the volume change of MoSe₂, ensuring the good stability of the electrode. The proposed approach can also be extended to other 2D transition metal chalcogenide (TMC) materials for constructing the TMC/C heterostructures for the application in energy storage systems.