Facile fabrication of bitter-gourd-shaped copper (II) tungstate thin films for improved photocatalytic water splitting

Copper (II) tungstate (CuWO4) has better light absorption and selectivity for a photochemical water-splitting reaction than those of its binary oxide counterpart. In this work, we report a facile single-step hydrothermal method to grow CuWO4 with a bitter gourd shape directly on a transparent conductive substrate for the first time. CuWO4 was synthesized via the condensation of a stable aqueous precursor solution of peroxopolytungstic acid and a copper precursor. The proposed method uniformly deposited CuWO4 on fluorine-doped tin oxide with strong adhesion. The obtained CuWO4 films showed a superior photocurrent density of 0.6 mA/cm2 at 1.23 V vs. a reversible hydrogen electrode in a 0.1 M Na2SO4 electrolyte, which was relatively higher than the values recently reported for CuWO4 photoanodes. The optimized CuWO4 exhibited an incident photon-to-current conversion efficiency of 30% at 350 nm for the photoelectrochemical oxidation of water. An X-ray photoelectron spectroscopy valence band edge analysis revealed an increase in the valence band edge position in the CuWO4, along with a decrease in the band gap compared to those in WO3. The procedure proposed here provides a promising approach for the design of an efficient CuWO4 photoanode for water splitting.