Fabrication and evaluation of TiO₂/multiwalled carbon nanotube composite thin-film photoelectrodes via sol–gel electrophoretic deposition using mixed solvents

Improvement in the photoelectrochemical activity of photoanodes is required to employ them in energy conversion systems. Various titanium dioxide (TiO₂) films have been combined with conductive materials using diverse methods to increase the photocatalytic activity of TiO₂. Recently, sol–gel electrophoretic deposition (EPD) was used to deposit composite thin films of TiO₂ and multiwalled carbon nanotubes (MWCNTs) with various structures by changing the ratio of TiO₂ sol to MWCNTs in an electrophoresis bath. Results indicated that the optimization of the chemical composition and morphology of the composite films are the key to improving the photoelectrochemical performance of TiO₂–MWCNT thin-film electrodes. Herein, the effects of solvents on the as-prepared thin-film structures were investigated using sol–gel EPD and the photoelectrochemical performance of the thin-film electrodes. Acetone was mixed with 2-propanol to increase the deposition rate—by decreasing viscosity—and modify the solvent affinity to each solute (i.e., TiO₂ sol and MWCNTs) to tune the chemical composition and morphology of the involved film for enhanced photoelectrochemical performance. The acetone/2-propanol volume ratio influenced the crystal structure (crystal size and anatase/rutile ratio) of TiO₂ as well as the chemical composition and morphology of the film. The highest photocatalytic activity was obtained at an acetone/2-propanol volume ratio of 1:9, an anatase/(anatase + rutile) ratio of 94.8 wt.%, and a TiO₂/C ratio of 39.4 wt.%, resulting in the largest ultraviolet adsorption by TiO₂ and the smallest charge transfer resistance.