Effect of Annealing Temperature on the Photoactivity of ITO/VO₂(M)/Au Film Electrodes for Water Splitting.

A metastable phase ITO/VO₂(B) film was prepared under the optimum conditions using a cyclic potentiometric device. Then, a monoclinic phase ITO/VO₂(M) film was prepared from the ITO/VO₂(B) film using annealing temperatures from 550 to 750 °C. From the XRD analysis, the crystallinity increases with the annealing temperature from 550 to 750 °C. The ITO/VO₂(M) film annealed at 750 °C had the optimum optical and structural properties. Then, three electrodes of ITO/VO₂(M)/Au were prepared: electrode (I), electrode (II), and electrode (III) at annealing temperatures of 550, 650, and 750 °C, respectively. The three electrodes were applied to generate hydrogen from H₂O and examined using the current-volt (I-V) relationship. Additionally, the incident photon-to-current conversion efficiency (IPCE) under monochromatic illumination was investigated. The electrode showed 4% efficiency at 25 °C and reached 8.1% at 45 °C. Finally, the different thermodynamic parameters, i.e., activation energy (Ea), enthalpy (ΔH*), and entropy (S*), were determined for electrode (III) to be 27.33 kJ mol-1, 124.93 kJmol-1, and 109.66 JKmol-1, respectively.