J. Georgieva

Morphology, Structure and Photoelectrocatalytic Activity of TiO2 / WO3 Coatings Obtained by Pulsed Electrodeposition onto Stainless Steel

A simple two-step pulsed electrodeposition/ electrosynthesis technique is employed for the preparation of a bicomponent photocatalyst, TiO2/WO3, onto metal substrates. TiO2 can be activated under UV light illumination and is well known for its water detoxification capabilities. The coupling between this wide band-gap semiconductor with a suitable narrow band-gap one, WO3, is used for effective separation of the photogenerated charge carriers. Besides the reduced surface recombinetion due to directional charge transfer, the combination with the visible light (Vis)-activated WO3 entails an extended photoactivity towards Vis wavelengths. In addition, the photocatalytic decomposition of organic water pollutants at TiO2/WO3 layers supported on conductive substrates can be further enhanced by applying a positive bias in an appropriate electrochemical cell. Drawing the electrons away from the surface through the external circuit reduces surface recombination rates of photogenerated electron-hole pairs. Recently, bilayer TiO2/WO3 photocatalysts were prepared onto stainless steel substrates by continuous cathodic electrodeposition of WO3 followed by TiO2 electrosynthesis [1, 2]. Their photoelectrocatalytic efficiency is very promising and superior to both their single-component counterparts. Also, there have been indications of the considerable impact of composition, morphology and structure on photoelectrocatalytic activity [3]. This implicates the necessity for appropriate monitoring and design of these factors. By applying a consecutive pulsed electrodeposition/electrosynthesis method for WO3 and TiO2, a favorable modification of the electronic properties at the TiO2-WO3 junction and an increased catalyst surface area has been sought. The morphology, structure and related composition distribution of the pulsed-deposited films onto metal substrates have been characterized by high resolution Field Emission SEM (FE SEM) (Fig. 1), SEMEDS and Raman spectroscopy. The photocurrents at photoanodes with various loadings, structure and morphology have been evaluated in the presence and absence of the model pollutants Na-oxalate and 4chlorophenol under UV and Vis light illumination. Similar to the case of continuous electrodeposition [3], a trend was observed of the impact and the need for optimization of the TiO2/WO3 loading ratio, surface morphology, structure and composition distribution to design high-performance photocatalysts. The performance for bulk photo-decomposition of 4-chlorophenol has been evaluated at photoanodes WO3 and TiO2/WO3 prepared by continuous electrodeposition and compared with that at pulsed-plated TiO2/WO3. Long-term photoelectrolysis at constant potential was applied, using spectrophotometry to monitor the variation of the pollutant concentration.