Facile Synthesis of a Pyrovanadate Ni2V2O7 Hollow Sphere/Reduced Graphene Oxide Nanocomposite as a Solid-State Hybrid Supercapacitor.

Nickel pyrovanadate (NVO) and compositing rGO in different concentrations with NVO are synthesized via the solvothermal process. XRD patterns reveal the formation of crystalline NVO and amorphous rGO in the nanocomposite. The morphology of the material resembles the formation of an NVO hollow nanosphere through a template-free synthesis route with the effect of ethylene glycol. From the CV oxidation and reduction curve, the battery-type faradic reaction is observed. The specific surface area increment via the rGO concentration increment in nanocomposites is due to the partially encapsulated hollow sphere on the 2D active surface area of rGO owing to better specific capacitance and electrochemical stability. In addition, the maximum specific capacitance of 3807 F g^-1 at 1 A g^-1 for NVO@rGO 20 is obtained via a three-electrode system. The solid-state device shows the specific capacitance retention of ∼70% even after 10,000 cycles for a scan rate of 10 A g^-1. The liquid electrolyte device shows the specific capacitance retention of ∼90% from its initial value and the successive charge-discharge process seen over the 10,000 cycles for the scan rate 10 A g^-1. The suitable device is identified from this work in terms of high stability, high specific capacitance, and excellent reversibility for electrochemical performance.