Effect of Thermal Treatment on the Crystallographic, Surface Energetics, and Photoelectrochemical Properties of Reactively Cosputtered Copper Tungstate for Water Splitting

摘要

In this Article, we report the effect of postdeposi-tion thermal treatment on reactively cosputtered copper tungstate (CuWO4) thin films and its impact on photoelectrochemical performances. This study indicates that CUWO4 films fabricated at 275 °C were amorphous and did not show significant photo-response in 0.33 M H3PO4 electrolyte when irradiated with air mass 1.5_(Global) simulated illumination. However, a major improvement in photoelectrochemical performance was observed in identical test conditions after a postdeposition treatment performed at 500 °C in pure argon for 8 h. Indeed, a photo- current density of approximately 400 μA cm~(-2) at 1.6 V vs saturated calomel electrode was measured on the annealed CuWO4 samples. Subsequent X-ray diffraction analysis revealed a clear transformation of as-deposited amorphous thin films into a triclinic CuWO4 structure after the annealing step. The polycrystalline CuWO4 films exhibited n-type conductivity, an indirect band gap of 2.25 eV, and a flat-band potential of -0.35 V vs saturated calomel electrode.