Nano- and micro-structural control of WO 3 photoelectrode films through aqueous synthesis of WO 3 ·H 2 O and (NH 4 ) 0.33 WO 3 precursors.

Nano- and micro-structured tungsten trioxide (WO 3 ) photoelectrode films were prepared through an aqueous solution route. WO 3 precursor layers were deposited on glass substrates through heterogeneous nucleation from (NH 4 ) 10 W 12 O 41 aqueous solutions at 50-60 °C. The crystal phase of the precursors changed from WO 3 ·H 2 O to (NH 4 ) 0.33 WO 3 with increasing (NH 4 ) 10 W 12 O 41 concentration ( x ), which involved a morphological change from micron-scale plates to nano-scale fine particles. The WO 3 ·H 2 O and (NH 4 ) 0.33 WO 3 layers were thermally converted to the monoclinic WO 3 phase. The fine-particle WO 3 films obtained from (NH 4 ) 0.33 WO 3 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 WO 3 films were obtained from WO 3 ·H 2 O layers, which exhibited strong light scattering in the visible range, and resulted in an enhanced photoanodic response at wavelengths above 375 nm.