Electrosynthesized TiO2 films: dependence of the brookite–anatase ratio on the applied potential

Abstract

TiO2 films were produced on ITO using a two-step method: (i) potentiostatic electrosynthesis of an amorphous titanium oxyhydroxide gel and (ii) subsequent crystallization by a thermal treatment (TT). The influence of applied potential on the morphology and on the crystalline structure of the resulting films was studied for three different TT temperatures, using SEM, XRD, and Raman spectroscopy. The films were porous and their morphology was more affected by the potential than by the temperature. The obtained TiO2 presented a high degree of crystallinity. The brookite–anatase coexistence was observed for all synthesis conditions. Nevertheless, the brookite content decreased for samples synthesized at more negative potentials, irrespective of the TT temperature. A relative estimate of brookite content variation among the prepared samples was obtained from an analysis of Raman spectra, and it was shown to be related with the pH variation during electrosynthesis. This correlation is in accordance with reported dependence of brookite-anatase ratio in sol-gel synthesis, which decreases with an increase in pH.