Metal oxides with moderate band gaps are desired for efficient production of hydrogen from sunlight and water via photoelectrochemical water splitting. Here, we report an α-SnWO4 photoanode with optical band gaps of 1.6 eV (indirect) and 2.3 eV (direct), synthesized by hydrothermal conversion of WO3 films. This photoanode is promising for overall photoelectrochemical water-splitting because the voltage of photocurrent onset is more negative than the potential of hydrogen evolution. Furthermore, the photoanode utilizes a large portion of the solar spectrum, with photon-current conversion observed at wavelengths up to 750 nm. However, the photocurrent density reaches only a small fraction of that which is theoretically-possible. Density functional theory-based thermodynamic and electronic structure calculations were performed to elucidate the nature and impact of defects in α-SnWO4 prepared by this synthetic route, from which hole localization at Sn-at-W anti-site defects was determined to be a likely cause for the poor photocurrent. Measurements further showed that the photocurrent decreases over time due to surface oxidation, which was suppressed by improving the kinetics of hole transfer at the semiconductor/electrolyte interface. Alternative synthetic methods and the addition of protective coatings and/or oxygen evolution catalysts are suggested to improve the photoelectrochemical performance and stability of this promising α-SnWO4 material.

Photoelectrochemical properties and behavior of α-SnWO4 photoanodes synthesized by hydrothermal conversion of WO3 films

253rd National Meeting (2017)

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