Effect of annealing environment on the electrochemical performance of biosynthesized V2O5@C thin films

Abstract

In the present work, the V2O5 thin films were prepared on flexible stainless steel mesh (FSSM) substrate using Bengal gram bean extract (BGBE) as a medium by reflux condensation method for its use as an electrode for supercapacitor application. The bio-molecules present in BGBE were in-situ converted into carbonaceous material after the annealing process. A systematic study of the influence of the annealing environment was investigated by heating the as-prepared V2O5 thin films in two different annealing atmospheres viz nitrogen and air. The annealing of the as-prepared V2O5 thin films under N2 atmosphere (V2O5-N) produces more carbonaceous material when compared to V2O5 thin films annealed in air atmosphere (V2O5-A). Interestingly, annealing in air atmosphere completely oxidizes the biomass, while annealing in nitrogen leaves traces of carbonaceous matrix in the thin film. This improves the conductivity and electrical properties of the material and its advantage is taken in fabricating supercapacitor devices. The obtained V2O5-N and V2O5-A thin films were characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman, and X-ray Photoelectron Microscopy (XPS). Moreover, the electrochemical performance of V2O5-N and V2O5-A was investigated. The V2O5-N electrode exhibited a specific capacitance (Csp) of 633.3 F g−1 with an energy density (ED) of 87.9 wh kg−1 at 2 mA cm−2 current density and good cycles stability with capacitive retention of 86.2 % over the 10,000 continuous GCD cycles which is higher than the V2O5-A. A flexible symmetric solid state (SSC) device was assembled using V2O5-N electrodes with PVA-LiClO4 gel electrolyte. The device exhibited a Csp of 82.6 F g−1 with an ED of 22.4 wh kg−1 at 1 mA cm−2 current density. In summary, the V2O5-N demonstrated significantly improved electrochemical performance than the V2O5-A electrode and is supported with the appropriate data.