Morphology-dependent enhancement of the electrochemical performance of CNF-guided tunable VS4 heterostructures for symmetric supercapacitors

Abstract

Alteration in the morphology of layered materials to improve storage capacity for electrical energy storage (EES) systems, including supercapacitors (SCs), provides enormous opportunities to impart unique structural features and tunable electrochemical properties. Herein, we prepared VS₄@CNF heterostructures via a solvothermal process where in situ growth of VS₄ (vanadium tetrasulfide) occurred at the CNF (carbon nanofiber) surface. Variation in the relative weight percentage of CNF to VS₄ (as VS₄@CNF_x/2x/3x) affected the morphology of the grown VS₄ from nanosheets to micro-flower. The as-synthesized VS₄@CNFs composite was investigated as the active electrode material for SCs. Growth of layered VS₄ at the CNF surface added advantages to the resulting materials by improving the conductivity as well as the charge acceptor sites during the SC cycling process. A concomitant hybrid morphology VS₄@CNF_2x electrode demonstrated excellent electrochemical performance, with a specific capacitance of 840 F g⁻¹ at 1 A g⁻¹ over a wide voltage range from −1.4 to 0.2 V, which outperforms pristine VS₄. Density functional theory (DFT) calculations showed the proximity of VS₄ on CNF allowed V–C bond formation, which resulted in an enhancement of the electronic states near the Fermi level compared to pure VS₄. Therefore, the improved capacitance for the VS₄@CNF heterostructure is due to the contribution of pseudocapacitance from the CNF, and benefits from the altered VS₄ morphology over CNF, which may facilitate electrolyte accessibility. The observed high charge storage capacity and the cycling reversibility with 86% capacity retention after 5000 cycles of the VS₄@CNF_2x symmetric device is credited to the robustness of the layered VS₄@CNF composite material. This study highlights the rational design of 2D materials@1D nanomaterials to provide better interfacial interaction and assist in the self-assembled hierarchical growth of hybrid materials, to satisfy the ever-growing needs in a wide arena of applications.