Nano- and micro-structural control of WO3 photoelectrode films through aqueous synthesis of WO3·H2O and (NH4)0.33WO3 precursors

Abstract

Nano- and micro-structured tungsten trioxide (WO₃) photoelectrode films were prepared through an aqueous solution route. WO₃ precursor layers were deposited on glass substrates through heterogeneous nucleation from (NH₄)₁₀W₁₂O₄₁ aqueous solutions at 50–60 °C. The crystal phase of the precursors changed from WO₃·H₂O to (NH₄)_0.33WO₃ with increasing (NH₄)₁₀W₁₂O₄₁ concentration (x), which involved a morphological change from micron-scale plates to nano-scale fine particles. The WO₃·H₂O and (NH₄)_0.33WO₃ layers were thermally converted to the monoclinic WO₃ phase. The fine-particle WO₃ films obtained from (NH₄)_0.33WO₃ layers showed a better photoanodic performance in the UV range below 350 nm, which was attributed to the larger surface area arising from the porous structure. On the other hand, platy-particle WO₃ films were obtained from WO₃·H₂O layers, which exhibited strong light scattering in the visible range, and resulted in an enhanced photoanodic response at wavelengths above 375 nm.