WO3 PHOTOANODE FOR ADVANCED OXIDATION PROCESSES Maliha Parvin, Milda Petrulevičienė, Irena Savickaja, Arnas Naujokaitis, Vidas Pakštas, Jurga Juodkazytė Center for Physical Sciences and Technology, Saulėtekio av. 3, Vilnius 10257, Lithuania maliha.parvin@ftmc.lt Electrochemical advanced oxidation processes (EAOPs) have received great attention recently as a promising technology for utilization of renewable solar energy to produce strong oxidants, e.g. reactive chlorine species (RCS), persulfate, hydrogen peroxide, percarbonate, etc [1]. Tungsten (VI) oxide (WO3) is an n-type semiconductor that has been widely investigated as a photoanode due to its relatively low cost, chemical stability, and ability to absorb visible light (bandgap is 2.5 - 2.8 eV) [2,3]. In this work, WO3 layers with different morphology and thickness (0.4–10 μm) have been prepared by two different chemical solution deposition methods (“peroxotungstic acid route” and “tungstic acid route”) and their performance in photoelectrochemical (PEC) generation of RCS and persulfate was tested. The crystalline structure and morphology of the coatings were analyzed by X-ray diffraction and scanning electron microscopy (SEM) techniques. Photoelectrochemical behavior was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. Iodometric and chromatometric titration methods were used to determine the amounts of photoelectrochemically produced RCS and S2O82-, respectively, to evaluate the faradaic efficiency (FE) of PEC processes. The morphology-dependent competition between possible photoanodic processes occurring on WO3 surface in the solutions of 0.5 M NaCl and 0.5 M H2SO4 was analyzed considering the specific adsorption and electrostatic interactions between the reacting species at rough electrified interfaces. It was demonstrated that chloride ions tend to adsorb specifically on the surface of WO3 electrodes, which provides them with a kinetic advantage over other solution species in the process of hole scavenging and leads to high Faradaic efficiencies (up to almost 100%) of PEC generation of reactive chlorine species (ClO− + ClO2−). FE of S2O82- formation ranged between 40 % and 80 % [4]. Hole-mediated formation of radical intermediates was suggested to explain the photoelectrochemical performance of prepared photoanodes. The stability of WO3 films during prolonged photoelectrolysis in 0.5 M NaCl and 0.5 M H2SO4 solutions was tested and antimicrobial effect of PEC generation of strong oxidants was demonstrated. The obtained results show that photoelectrochemical systems with WO3 can find application in visible light-assisted advanced oxidation processes in the areas of water disinfection and organic pollutants degradation. [1] F. C. Moreira, R. A. R. Boaventura, E. Brillas, and V. J. P. Vilar, Electrochemical advanced oxidation processes: A review on their application to synthetic and real wastewaters, Appl. Catal. B. 202, 217–261, (2017). [2] K. Sayama, Production of high-value-added chemicals on oxide semiconductor photoanodes under visible light for solar chemical-conversion processes, ACS Energy Lett. 3,1093–1101, (2018). [3] J. C. Hill and K. S. Choi, Effect of electrolytes on the selectivity and stability of n-type WO3 photoelectrodes for use in solar water oxidation, J. Phys. Chem. C 116, 7612–7620, (2012). [4 ] M. Parvin, M. Petrulevičienė, I. Savickaja, B. Šebeka, R. Karpicz, A. Grigucevičienė, R. Ramanauskas, J. Juodkazytė, Influence of morphology on photoanodic behaviour of WO3 films in chloride and sulphate electrolytes, Electrochim. Acta 403,139710, (2022). Acknowledgment: This research was funded by the M-ERA.NET project “Multiscale computer modelling, synthesis and rational design of photo(electro)catalysts for efficient visible-light-driven seawater splitting” (CatWatSplit), Ref. Number: project8168, under a grant agreement Nr. S-M-ERA.NET-21-3 with the Research Council of Lithuania(LMTLT).