A Facile Design of Solution-Phase Based VS₂ Multifunctional Electrode for Green Energy Harvesting and Storage

This work reports the fabrication of vanadium sulfide (VS₂) microflower via one-step solvo-/hydro-thermal process. The impact of ethylene glycol on the VS₂ morphology and crystal structure as well as the ensuing influences on electrocatalytic hydrogen evolution reaction (HER) and supercapacitor performance are explored and compared with those of the VS₂ obtained from the standard pure-aqueous and pure-ethylene glycol solvents. The optimized VS₂ obtained from the ethylene glycol and water mixed solvents exhibits a highly ordered unique assembly of petals resulting a highly open microflower structure. The electrode based on the optimized VS₂ and exhibits a promising HER electrocatalysis in 0.5 M H₂SO₄ and 1 M KOH electrolytes, attaining a low overpotential of 161 and 197 mV, respectively, at 10 mA.cm^-2 with a small Tafel slope 83 and 139 mVdec^-1. In addition, the optimized VS₂ based electrode exhibits an excellent electrochemical durability over 13 h. Furthermore, the superior VS₂ electrode based symmetric supercapacitor delivers a specific capacitance of 139 Fg^-1 at a discharging current density of 0.7 Ag^-1 and exhibits an enhanced energy density of 15.63 Whkg^-1 at a power density 0.304 kWkg^-1. Notably, the device exhibits the capacity retention of 86.8% after 7000 charge/discharge cycles, demonstrating a high stability of the VS₂ electrode.