Mesoporous thin film WO3 photoanode for photoelectrochemical water splitting: a sol–gel dip coating approach

Abstract

A facile and cost-efficient method to fabricate a mesoporous structured WO₃ photoanode was implemented for use in a tandem dual photosystem water splitting photoelectrochemical cell. Semi-transparent thin films of tungsten trioxide were fabricated by sol–gel process, incorporating a block co-polymer to induce a template-directed mesoporous structure. These thin films are deposited by dip coating onto transparent conducting oxide substrates and crystallized at a low temperature of 400 °C in air. These WO₃ photoanodes exhibit a photocurrent of up to 0.6 mA cm⁻² in potassium phosphate buffers of pH 2, 4, and 6 at 1.23 V vs. RHE under 300 mW cm⁻² visible (400–900 nm) light irradiation with a faradaic efficiency of up to 75%. Furthermore, we have demonstrated that corrosion occurs in electrolytes of pH > 4. The faradaic efficiencies in varying pH solutions suggest that parasitic redox reactions occurs in acidic conditions, limiting the O₂ production and demonstrating the need for stable surface co-catalysts to increase faradaic efficiencies. In neutral conditions, protective layers and/or co-catalysts are needed for increasing WO₃ photoanode stability.