A simple route for preparation of textured WO3 thin films from colloidal W nanoparticles and their photoelectrochemical water splitting properties

• W nanoparticles were synthesized via a wet-chemistry method.
• Spin-coating of W nanoparticles onto FTO substrates yielded uniform W films.
• Oxidation of W films at high temperature allowed the preparation of textured WO3 films.
• The WO3 films were used as photoanode in photoelectrochimical water splitting.

Colloidal tungsten (W) nanoparticles (NPs) were synthesized by pyrolysis of W(CO)6 precursor in a mixture of 1-octadecene, oleylamine and oleic acid at ∼230 °C under Ar atmosphere. The metallic W NPs were spin-coated on fluorine-doped tin oxide (FTO) substrates and later were transformed to WO3 phase by heat treatment at 500 and 550 °C. We prepared WO3 thin films with different thicknesses which we used in photoelectrochemical water splitting. The highest achieved photocurrent was ∼830 μA/cm2 at 1.9 V vs. reference reversible hydrogen electrode (RHE) with the 900 nm thick WO3 film. Incident photon-to-current conversion efficiency (IPCE) showed that the quantum efficiency of WO3 thin films can reach up to 66% at 320 nm. Characterization of W NPs and WO3 thin films was carried out with UV–vis absorption spectroscopy, diffused reflectance spectroscopy, X-ray diffraction, transmission electron microscope and scanning electron microscope. The procedure given herein is a novel fabrication approach for the preparation of textured WO3 thin films where metallic W NPs are used as a precursor material. The proposed method can be generalized and extended to the preparation of other types of textured metal oxide thin films.

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