Tailoring the Film Thickness of Template-Assisted Sol–Gel-Derived Porous WO3 Photoanodes for Highly Efficient Photoelectrochemical Water Oxidation

Photoelectrochemical hydrogen production is a promising and cost-effective strategy to provide clean and sustainable fuel. Due to its excellent electrical and optical properties, tungsten trioxide (WO₃) is one of the most studied electrode materials in this field, and it is well known that the incorporation of pores into the semiconductor can improve its photoelectrochemical performance. Using a facile and scalable template-assisted sol–gel technique, porous WO₃ thin films were tailored by simply varying the number of dip coating cycles. By crystallizing these films at 400 °C, a $$-orthorhombic/$$-monoclinic crystal structure and an average surface area of 32 m² g⁻¹ were obtained. By optimizing the layer thickness of these photoanodes on fluorine-doped tin oxide, photocurrents of up to 3.3 mA cm⁻² at 1.23 V_RHE (in 0.1M H₂SO₄, pH = 0.71) were achieved without the use of any co-catalysts or sacrificial agents. Our photoelectrodes also showed highly reproducible photocurrents, and their high stability was proven in cycling tests, long-term measurement and post-photoelectrochemical characterization. Our work represents a very simple preparation optimization to achieve high-performing WO₃ photoanodes for photoelectrochemical applications.