THE EFFECT OF STABILIZING AGENTS IN SOL-GEL SYNTHESIS OF BiVO4 COATINGS

Donatas Pleškys; Irena Savickaja; Vidas Pakštas; Arnas Naujokaitis; Jurga Juodkazytė; Milda Petrulevičienė

Open Readings 2021 • P6-49

THE EFFECT OF STABILIZING AGENTS IN SOL-GEL SYNTHESIS OF BiVO₄ COATINGS

Donatas Pleškys¹, Irena Savickaja², Vidas Pakštas², 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]

Recently, photoelectrochemical (PEC) sensing techniques have attracted substantial research interest in the area of detection of biomolecules. Compared to conventional electrochemical methods, the PEC sensor has high sensitivity and a low background signal, which can be ascribed to its separate excitation source and detection signals [1]. Efficiency of PEC systems strongly depends on photoanodes, which convert the energy of visible light into chemical energy. Among the various photoelectrodes studied for PEC applications, monoclinic bismuth vanadate (BiVO₄) is considered to be a promising material owing to its moderate band gap (2.4 eV) and appropriate band-edge positions, which allow it to absorb as much as 11% of the solar spectrum. Nevertheless, the photocatalytic activity of bare BiVO₄ is still not ideal for practical applications because of its excessive charge recombination, poor charge transport, and slow oxidation kinetics [2].

In our work citric acid, urea and polyethylene glycol (PEG) were used as stabilizing agents for formation of BiVO₄ thin films in sol-gel approach. Organic additives serve as complexing agents of Bi³⁺ ion, therefore different morphology and photoelectrochemical properties of BiVO₄ coatings are obtained. Ratio of citric acid and PEG to BiVO₄ was chosen to be 2:1, however ratio of urea to BiVO₄ was 0.5:1, because at higher amounts of urea formation of precipitates occurred. After dip-coating of BiVO₄ on conducting glass (FTO) substrate all samples were annealed at 450°C for 2h. Crystallinity and morphology of coatings were evaluated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Photoelectrochemical response of obtained coatings were analyzed using cyclic voltammetry in three electrode cell in 0.5M Na₂SO₄ solution in the dark and under illumination (Fig. 1). Photoelectrochemical oxidation of glucose was studied in three electrode cell in sodium borate buffer (pH=9) with 5-35mM of glucose.

**Fig. 1.** Cyclic voltammograms of BiVO₄ electrodes in 0.5 M Na₂SO₄ solution; potential scan rate 50 mV/s, intensity of illumination ~ 100 mW cm^-2

Obtained results revealed, that different stabilizing agents strongly influence morphology and PEC activity of the coatings. The highest photocurrent was obtained for coating synthesized with urea (Fig. 1). Photoelectrochemical oxidation of glucose showed the linear enhancement of photocurrent with increased concentration of glucose in the range of 5~35 mM. Obtained sensitivity of BiVO₄ for glucose detection will be evaluated and presented.

[1] S. Wang, S. Li, W.Wang et al. A non-enzymatic photoelectrochemical glucose sensor based on BiVO₄ electrode under visible light, Sensors and Actuators B: Chemical, 291, 34-41 (2019).

[2] L. Xia, J. Li, J. Bai et al. BiVO₄ Photoanode with Exposed (040) Facets for Enhanced Photoelectrochemical Performance, Nano-micro Letters 11, 1-10 (2018).