Electrochemical performance investigation of electrospun urchin-like V₂O₃-CNF composite nanostructure for vanadium redox flow battery

Home-made electrospun catalyst based on urchin-like vanadium (III) oxide-carbon nanofiber (V₂O₃-CNF) composite is synthesized from a solution containing vanadium (V) oxytriisopropoxide VO-(OiPr)₃ as metal oxide precursor and polyvinylpyrrolidone (PVP) as carbon source for vanadium redox flow battery (VRFB) application. X-ray diffraction (XRD) as well as scanning electron microscopy (SEM) analysis show a typical V₂O₃ rhombohedral structure and an urchin-like V₂O₃-CNF morphology, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements show a high electrocatalytic activity for the composite electrospun samples both in terms of peak to peak separation (ΔE = 0,02 V) and lower charge transfer resistance (R_ct = 0.12 ohm cm²) with respect to a pristine CNF. The better reversibility is ascribed to the oxygen functional groups presence that act as catalytic sites reducing kinetic overpotentials. Moreover, thanks to the rhombohedral structure of V₂O₃, as well as to the more graphitic structure of the carbon, a suitable electrical conductivity is guaranteed for reducing ohmic overpotentials.