Effects of Heat Treatment and Electrolyte Type on the Properties of Vanadium Pentoxide

Abstract

In this work, the effect of heat treatment in the synthesis of vanadium pentoxide (V₂O₅) on its physicochemical properties was studied. Furthermore, the effect of liquid and viscous electrolytes based on lithium perchlorate (LiClO₄) on the performance of electrochromic devices (ECDs) was evaluated using heat-treated V₂O₅ as electrochromic film. V₂O₅ was synthesized using the chemical bath technique. The V₂O₅ without and with heat treatment at 400 °C was characterized using FT-IR, UV-Vis, XRD, XPS, FESEM, AFM, and cyclic voltammetry (CV) techniques. Better physicochemical behavior was shown by the thermally treated V₂O₅, which is why it was used in the ECDs. Single ECDs were characterized using optical transmittance spectra, kinetic curves, and electrochemical impedance spectroscopy. A broadening of the absorption band towards the red and better electrochemical properties were observed when a thermal treatment was applied to the amorphous V₂O₅. A charge storage capacity of 1061.42 mC/cm² was obtained for the crystalline V₂O₅ film (with heat treatment) compared to the charge storage capacity of 303.38 mC/cm² obtained for the amorphous V₂O₅ film. A better distribution and decrease in grain size was observed for V₂O₅ with heat treatment. The CV curves showed higher stability of crystalline V₂O₅ compared to amorphous V₂O₅, even after several cycles and at different scan rates. A higher flow of ions between the working electrode and the counter electrode was achieved with the use of liquid electrolyte in the ECD, allowing a more efficient ECD with greater change in transmittance in the near-infrared region, compared to the use of viscous electrolyte. This research work contributes to the improvement of the physicochemical properties of V₂O₅.

Graphical Abstract