WO3 coatings for photoelectrochemical synthesis of persulfate: efficiency, stability and applicability

Light-assisted electrochemical processes have the potential to replace energy-intensive electrosynthesis technologies, especially in the area of strong oxidant production. The efficiency of photoelectrochemical (PEC) synthesis relies mainly on the properties of a photoanode. PEC reaction as a multistep process, involving light absorption, charge carrier generation, separation, transport and transfer across electrode/electrolyte interface, is strongly dependent on the morphology, crystallinity and structural properties of the semiconductor layer. In this study, light-sensitive tungsten (VI) oxide, WO3, films were formed applying a simple chemical solution deposition technique. Formation conditions were modified by using four different alcohols (methanol, ethanol, isopropanol and butanol) as reductants and different annealing temperatures. Detailed morphological, structural and compositional characterization of WO3 samples was performed by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. Significant differences in surface morphology and crystallinity of the films were observed. PEC activity of the synthesized coatings was evaluated in sulfuric acid solution, where photocurrent stability and variation of Faradaic efficiency of persulfate generation were investigated. Possible causes of photocurrent decay and WO3 surface passivation are discussed. Applicability of the system for deactivation of Bacillus spp. bacteria under visible light illumination is demonstrated.