Tailored preparation of WO₃ nano-grassblades on FTO substrate for photoelectrochemical water splitting

WO₃ nano-grassblades (NGs) were successfully synthesized on a fluorine-doped tin dioxide (FTO) substrate by a two-step hydrothermal method, which involves a nanoseed-generating step and a nano-grassblade-growth step using urea as the morphology-controlling agent. The influence of the seeding procedure on the morphology of the obtained WO₃ nanostructure was systematically investigated. The synthesized WO₃ NGs were revealed to have a single crystalline structure with a large aspect ratio and perpendicular alignment on FTO substrates. The photoelectrochemical (PEC) water splitting properties of the annealed WO₃ NGs were performed in 0.1 M KH₂PO₄/K₂HPO₄ buffer solution (pH 7), exhibiting an onset potential of ca. -0.1 V vs. SCE and a maximum photocurrent density of 1.2 mA cm^-2 under 1.5 G illumination. Growth time-dependent PEC activity and specific surface area data confirm that the efficient PEC activity of WO₃ NGs is attributed to their high specific surface area, which is beneficial in enlarging the WO₃/solution interface for water oxidation. This two-step hydrothermal growth technique demonstrates a unique advantage in ensuring firm adhesion of the WO₃ film to the FTO substrate and offers a novel route for improving the performance of PEC water splitting devices.