(Photo)Electrochemical characterization of nanoporous TiO2 and Ce-doped TiO2 sol–gel film electrodes

• Published in: Electrochimica acta 2012-11, Vol.83, p.113-124
• Main Authors: Kityakarn, Sutasinee, Pooarporn, Yingyot, Songsiriritthigul, Prayoon, Worayingyong, Attera, Robl, Simone, Braun, André M., Wörner, Michael
• Format: Article
• Language: English
• Subjects: Ce-doped TiO2; Chemistry; Density; Electrochemical impedance spectroscopy; Electrochemical impedance spectroscopy (EIS); Electrochemistry; Electrodes; Exact sciences and technology; General and physical chemistry; Nanocomposites; Nanoporous TiO2 film electrode; Nanostructure; Photocurrent; Photoelectric effect; Photoelectrochemistry; Photoelectrochemistry. Electrochemiluminescence; Porous electrode model; Titanium dioxide
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2012.07.129

► Prevention of rutile phase formation by cerium doping. ► Observation of a photo-current maximum in dependence of the TiO2 film thickness. ► Limitation of photocurrent at higher radiant power by electron–hole recombination. ► Current doubling and suppression of charge recombination by methanol addition. ► 3D array of nanoparticles shows features similar to a solid crystalline electrode. Focusing on effects of charge separation limitations and doping on the photoactivity of TiO2, different nanoporous TiO2 film electrodes were prepared by the sol–gel or the suspension methods, respectively. X-ray diffraction (XRD) characterization revealed for all undoped TiO2 electrodes (TiO2-SG and TiO2-P25) mixed phases of anatase and rutile, whereas the 2%CeTiO2-SG electrode showed only anatase phase pattern, revealing that the incorporation of Ce ions prevented phase transformation. The (photo)electrochemical characterization of the nanoporous TiO2 film electrodes was performed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the dark and under UV irradiation, respectively. A photocurrent maximum depending on the film thickness was observed at about 13μm for all TiO2 electrodes investigated. The photocurrent responses of Ce-doped sol–gel TiO2 electrodes were comparably low, indicating an enhanced electron–hole recombination at the Ce ion levels within the band gap of TiO2. A porous electrode model was adapted for the fitting of the experimental EIS data. The potential and incident radiant power density dependence of the heterogeneous charge transfer reaction (RCT) and the coupled transport of photogenerated electrons to the collector electrode (ZS) were ascribed to promoted charge carrier separation and migration, i.e. electron drift dominated over diffusion. Consequently, the dependence of different discrete impedance elements was discussed, supposing a macroscopic electric field across the 3D array of interconnected TiO2 nanoparticles that form the film electrodes. Besides photocurrent doubling, addition of methanol as a hole scavenger revealed the limitation of the overall reaction by the heterogeneous charge transfer reaction, in particular at high radiant power densities.