Synergistic effect of redox couple VO²⁺/VO₂⁺ with H₃PO₄ to enhance the supercapacitor performance

The purpose of this paper is to give a comprehensive study on the effect of redox additive (VOSO₄) and the properties of supercapacitor. In this study, for the electrode of supercapacitor, carbon based material (synthesized from eucalyptus leaves) is used. This electrode material is characterized by using the X-ray diffraction, Raman spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy techniques that confirm its well porous structure in graphitic conducting phase and its ability to use as an electrode material. Fabricated supercapacitor cells, by using H₃PO₄ and H₃PO₄ added VOSO₄ electrolytes, are tested with electrochemical impedance spectroscopy, cyclic voltammetry and charge–discharge techniques. The cell consisting H₃PO₄ + VOSO₄ has provided 5–6 times higher capacitive performance than what observed with its pristine H₃PO₄ counterpart. The maximum specific capacitance and energy detected using H₃PO₄ were 117.6 F g⁻¹ and 8.6 Wh kg⁻¹ whereas the same parameters were found 704.1 F g⁻¹ and 52.2 Wh kg⁻¹, respectively for the VOSO₄ based system. Maximum specific power, so it was also obtained higher (9.2 kW kg⁻¹) for redox system than the pristine one (7.9 kW kg⁻¹). The credit for this performance goes to the VO²⁺/VO₂⁺ redox couple as well as the functional groups present in the active material. Furthermore, the cycle life, open circuit potential and thermal effects have been explored for the fabricated cells and in all those tests VOSO₄ based redox system got succeed to leave its ample effect on the supercapacitor performance, positively.