Synthesis of transparent mesoporous tungsten trioxide films with enhanced photoelectrochemical response: Application to unassisted solar water splitting

Tungsten trioxide (WO₃) films with a mesoporous morphology, high transparency, and monoclinic phase crystallinity were prepared using polyethyleneglycol (PEG) as a surfactant and their photoelectrochemical properties were measured. By controlling the weight ratio of the tungsten precursor to PEG, a sphere-like WO₃ nanoparticle film with high transparency can be synthesized. The photocurrent responses of the films under 1 sun solar light illumination were measured. Due to the high transparency of the WO₃ photoanode, it is possible to fabricate a tandem cell composed of a WO₃/Pt bipolar electrode connected with a dye-sensitized solar cell. Unassisted water splitting from the tandem cell was demonstrated but the maximum current density was exhibited at around +0.4 V (vs. Pt).