Synthesis of α-SnWO4 thin-film electrodes by hydrothermal conversion from crystalline WO3

Thin film electrodes of the orthorhombic form of tin tungstate (α-SnWO4) were prepared using a hydrothermal method to convert thin films of WO3 in aqueous SnCl2. The pH dependence of the growth mechanism was identified by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD patterns show complete conversion of WO3(s) to SnWO4(s) at pH 1, 4, and 7. SEM images reveal a morphology change from sponge-like platelets to sharp nanowires as the pH increases from 1 to 7. The α-SnWO4 thin films were reddish brown in color, and display an indirect band gap of 1.9 eV by diffuse reflectance UV–vis spectroscopy. α-SnWO4 is therefore solar-responsive, and a chopped light linear sweep voltammogram recorded under 100 mW/cm2 AM1.5 simulated solar illumination in a pH 5 0.1 mol/L KPi buffer show a visible light response for photoelectrochemical water oxidation, producing 32 μA/cm2 at 1.23 V vs. RHE.

Graphical abstractMonoclinic WO3 films were converted to orthorhombic α-SnWO4 by a hydrothermal method. The resulting films show a visible light response for photoelectrochemical water oxidation.Figure optionsDownload full-size imageDownload as PowerPoint slide