WO3 photoanodes for photoelectrochemical applications

WO₃ layers were prepared by spray pyrolysis of a peroxotungstic acid solution on FTO/glass substrates. Investigated parameters were layer thickness and influence of post-annealing in air. Films deposited at 250 °C were amorphous. Post-annealing at 550 °C for 2 h resulted in the formation of monoclinic crystalline structure. A comprehensive account of electrochemical efficiency in terms of IPCE for WO₃ films as a function of the three parameters (wavelength, thickness and direction of light incidence) fully characterizing the photoelectrodes is presented here for the first time. The highest improvement in crystallinity and also the highest photocurrent response was found for WO₃ layers deposited at 250 °C and post-annealed at 550 °C, namely 1.9 mA/cm² (in 0.1 M HClO₄ at 1.6 V vs. Ag/AgCl) under irradiation with a solar simulator (AM 1.5, 100 mW/cm²) and IPCE = 0.5 at 369 nm (front side irradiation), which is comparable with values obtained by other deposition techniques (e.g., hydrothermal or sol gel). Spray pyrolysis as a method of fabricating WO₃ electrodes has the advantage of being able to produce large electrodes for use in practical applications.