ᐊ P5-2
Open Readings 2021 • P5-3
P5-4 ᐅ

OPTIMIZATION OF SOL-GEL SYNTHESIS PROCEDURE OF TUNGSTEN (VI) OXIDE COATINGS FOR EFFICIENT PHOTOELECTROCHEMICAL PRODUCTION OF HYPOCHLORITE

Evelina Griniuk1, 2, Irena Savickaja2, Arnas Naujokaitis2, Jurga Juodkazytė2, Milda Petrulevičienė2

1 Institute of Chemistry, Faculty of Chemistry and Geosciences, Naugarduko str. 24, LT-03225 Vilnius University, Lithuania

2 Center for Physical Sciences and Technology, Department of chemical engineering and technology Saulėtekio av. 3, LT-10257 Vilnius)

[email protected]

Photoelectrochemical (PEC) techniques have received a lot of attention because they provide insights into the utilization of solar energy for sustainable production of hydrogen and other chemicals, degradation of organic pollutants, generation of electricity in photofuel cells, etc. A pivotal challenge to realize PEC applications in practice is development of efficient photoelectrode materials [1-3].

Many semiconductor metal oxides, such as TiO2, WO3, BiVO4 and α-Fe2O3, have been intensely investigated as photoelectrodes due to their high chemical stability in oxidation conditions and reasonably high incident light-to-current conversion efficiencies. Among them, WO3 is a promising photoanode material for its moderate band gap of 2.5–2.7 eV, which allows absorbing ~12% of solar spectrum with a theoretical maximum energy conversion efficiency of ~6.3% [1].

In this work, WO3 thin films on conductive glass (FTO) substrate were synthesized using sol-gel method and dip-coating technique. Coatings were modified using different amount of polyethylene glycol (PEG) in order to evaluate the influence of this additive on photoelectrochemical response of the layers. The synthesis was carried out at 85°C for 180 minutes using different Na2WO4 to PEG ratios of (1:1; 1:2, 1:0.5; 1:0.1). Coatings were annealed at 400°C for 2 h in air. The composition and surface morphology of the coatings were investigated using X-ray diffraction and scanning electron microscopy (SEM) techniques. Photoelectrochemical response was investigated by cyclic voltammetry in three electrode cell in 0.5 M H2SO4 solution in the dark and under light irradiation. Chronoamperometry in two-electrode set-up along with titrimetric analysis were used to evaluate the Faradaic efficiency of photoelectrochemical hypochlorite production with WO3 photoelectrodes in NaCl solution.

Figure 1
Fig. 1. Top view SEM images of WO3 films synthesized with different Na2WO4 to PEG ratios: 1:0.1 (a), 1:0.5 (b), 1:1 (c) and 1:2 (d).

It was found that different amount of PEG used in sol-gel synthesis strongly influences morphology of the WO3 coatings (Fig. 1). All coatings were photoelectrochemically active, however the highest photocurrent of 0.7 mA cm-2 at 1.6 V (Ag/AgCl) was found for the coating synthesized with Na2WO4:PEG molar ratio of 1:0.5, which means that these synthesis conditions ensure the most effective generation and transport of photogenerated charge carriers in the oxide layer. Faradaic efficiency of hypochlorite formation ranged between 64 – 67%.

Acknowledgments: This research is funded by the European Social Fund under the No 09.3.3-LMT-K-712-22-0185 "Development of Competences of Scientists, other Researchers and Students through Practical Research Activities” measure.

[1] Q. Zeng, J. Li, J. Bai, X. Li, L. Xia, B. Zhou, Preparation of vertically aligned WO3 nanoplate array films based on peroxotungstate reduction reaction and their excellent photoelectrocatalytic performance, Applied Catalysis B: Environmental 202, 388-396 (2017)

[2] K. Sayama, Production of High-Value-Added Chemicals on Oxide Semiconductor Photoanodes under Visible Light for Solar Chemical-Conversion Processes, ACS Energy Letters 3 (5), 1093-1101 (2018).

[3] W. Yang, R. Ramanujam Prabhakar, J. Tan, S. David Tilley, J. Moon, Strategies for enhancing the photocurrent, photovoltage, and stability of photoelectrodes for photoelectrochemical water splitting, Chemical Society Reviews 48, 4945-5178 (2019).