Electrochemical Characterization of TiO[sub 2] Films Formed by Cathodic EPD in Aqueous Media

Abstract

The present work studies the influence of applied electric field on the cathodic electrophoretic formation of TiO 2 films in an aqueous medium. The growth of the film was followed by measuring current density, deposited mass, and thickness under imposed electric field ͑͒. In scanning electronic microscopy images of the TiO 2 films formed under different electric fields, three regions can be seen: ͑i͒ formation of nuclei that are converted into agglomerates, ͑ii͒ uniform and one-sided growth, and ͑iii͒ growth by the formation of agglomerates on the TiO 2 surface. The characterization of semiconductor properties showed that increased for film growth leads to an increase in the density of donors and to a displacement of the flatband potential toward less negative values. The photoelectrochemical characterization of the oxide films revealed that the photoelectrochemical performance of the TiO 2 films decreases as a function of the electric field used to carry out the electrophoretic deposition ͑EPD͒ process. The electrochemical behavior observed for these films seems closely related to the content of Ti 3+ doping sites electrogenerated in situ during the EPD, which act as electron traps negatively affecting the electron transport toward the indium tin oxide collector, also making their photoelectrochemical activity inefficient.TiO 2 is the material that has been most frequently employed in photoelectrochemical cells because of its unique properties, such as high stability, high photocatalytic activity, and relatively low cost. 1-14 However, TiO 2 is generally found as a particulate material and requires processing for the formation of a film that allows its application in photoelectrochemical cells ͑with stability, high surface area, and good activity͒. Among different techniques proposed in the literature for the preparation of these films, the best for its application on an industrial scale, due to its relatively low cost and good reproducibility, is the electrophoretic deposition ͑EPD͒. 15 Although it has not been extensively employed in the preparation of photoanodes, the results achieved so far using this technique are promising and prove that semiconductive oxide films can be easily prepared from stable colloidal suspensions that exhibit good stability and photoelectrochemical performance. 7,8 The EPD technique is feasible for the preparation of films of different semiconductive materials; for instance, Kim et al. 6 employed EPD in the fabrication of solar cells with TiO 2 nanotubes and obtained a solar energy performance 6.72% higher than that achieved using the doctor blade method, whose efficiency was just 0.65%. The EPD has also been useful in the preparation of films made of composed materials, such as TiO 2 /PTh, 12 TiO 2 /C, 2 and TiO 2 nanotubes modified with WO 3 . 5 Likewise, it has been used to characterize the photoelectrochemical properties of materials such as WS 2 , SnS 2 , 16 and K 4 Nb 6 O 17 . 17 One important characteristic of the EPD is that it has different operating variables that allow al...

Formation of TiO2 photoanodes by simultaneous electrophoretic deposition of anatase and rutile particles for photoassisted electrolytic copper ions removal

“…The suspensions employed for the tests constituted 100 mg of TiO 2 in 1 L of a solvent composed by 5.0% v/v 2-propanol and distilled water. 18,19 For the measurements of electrophoretic mobility (m) versus pH, 0.1 M NaOH and HCl solutions were used to change the pH of the suspensions. The evaluation of the dispersant effect in m of TiO 2 particles was carried out for a concentration range of between 0.0 and 1.0% w/w.…”

“…Baker 99.97%) and distilled water, with 500 mg of TiO 2 , in an ultrasonic bath for 10 min. 18,19,24 The quantity of Anatase and Rutile added was 500 mg, but the Anatase fraction in the powders was changed (1.0, 0.8, 0.7, 0.5, 0.0). As the TiO 2 acquire a negative surface charge in the suspension, the stainless steel foils, employed as substrates for the films, were used as anodes while another stainless steel foil was used as a cathode.…”

“…Both foils were set at 2 cm and parallel to each other. The deposition was carried out in a manner similar that reported in earlier studies, reported before 18,19 but in this case, a field of 6 V/cm for 40 s was applied. After the electrophoretic deposition of TiO 2 particles, the films were withdrawn from the suspensions and dried in a desiccator.…”

“…18,19 Additionally, this technique offers the simultaneous and homogeneous growth of multicomponent films, allowing the deposition of different materials without altering physicochemical properties. [20][21][22][23] With this methodology, commercial materials can be used to form films with tailored properties, improving photo-reactivity.…”

Photo-assisted electrochemical copper removal from cyanide solutions using porous TiO2 thin film photo-anodes

“…In this system, the metals ions are reduced over a metallic electrode allowing its recovery, or just making easier its disposal. Additionally, due to the imposed potential, oxidation of the complex forming agent can occur at the photo-anode, avoiding the hole scavenger addition in the solution 15 . One of the most common methodologies for the elaboration of supported TiO 2 on conductive substrates is the combination of the Sol-gel process and the dip-coating or spin-coating techniques 16 , due to the low sintering temperatures required, versatility of the processes and homogeneity at molecular level 17 .…”