In this paper, the electrochemical impedance spectroscopy (EIS) mathematical model of TiO2 photoelectrocatalytic (PEC) reactions involving charge transfer and recombination through surface states was developed. The model was used to study the kinetics of photoelectrocatalytic decomposition of salicylic acid. The model simulation results show that the appearance of two distinguishable semicircles in the EIS response depends on the charging of surface state and light intensity. The experimental results demonstrated that similar phenomena to the theoretical simulation results. The model provides a way to obtain the rate constants for the photoelectrochemical reactions of surface states mediating charge transfer and recombination. The applied potential changes not only the recombination rate constant but also the charge-transfer rate constant. Moreover, the experimental EIS results here and those previous published on PEC degradation reactions can be explained by the present model satisfactorily. The relevance of surface states was discussed briefly. The results demonstrated that EIS is a powerful tool for studying the kinetics of PEC decomposition of organic pollutants on TiO2 electrodes.

We report on the mechanism of water splitting by TiO 2 in the absence of chemical scavengers in a fully functional photoelectrochemical (PEC) cell. The application of a positive potential to a nanocrystalline-TiO 2 film is shown to lead to the formation of long-lived holes which oxidize water on the milliseconds time scale. These first time-resolved studies of a nanocrystalline-TiO 2 (nc-TiO 2 ) film in a complete PEC cell also showed that all of the long-lived photoholes go on to generate O 2 , and that there are no major branching inefficiencies in the catalysis itself, which appears to be operating at efficiencies close to 100%. The overall quantum yield of oxygen production under pulsed illumination (355 nm) was found to be ∼8% at excitation densities of 4.4 photons per particle. Under all conditions examined, electron-hole recombination was found to be the dominant loss pathway.

Nanocrystalline TiO 2 films were prepared on conductive fluorine doped glass (FTO, TEC-15, Hartford glass) and coverslip (50 µm thick) by the doctor blade method using Scotch tape as the spacer, prior to use the glass was sonicated in acetone and water for 30 minutes each, dried in air and then placed in a furnace at 450 o C in air for 30 minutes. The film thickness was measured using a profilometer (Alpha-Step 200, Tencor Instruments) and found to be approximately 4 μm for each tape spacer layer used. Thicker films were obtained by increasing the number of tape layers, thinner films were made using a k-bar. The TiO 2 films on FTO were cut to approximately 1.0 cm × 2.5 cm pieces with TiO 2 film covering a surface area of 1.0 cm × 1.5 cm. To make a photoelectrode, an electrical contact was made with FTO substrate by using silver conducting paste connected to a copper wire which was then enclosed in a glass tube. The working geometric surface area of TiO 2 was 1.0 cm × 1.0

Because n‐butanol as a fuel additive has more advantageous physicochemical properties than those of ethanol, ethanol valorization to n‐butanol through homo‐ or heterogeneous catalysis has received much attention in recent decades in both scientific and industrial fields. Recent progress in catalyst development for upgrading ethanol to n‐butanol, which involves homogeneous catalysts, such as iridium and ruthenium complexes, and heterogeneous catalysts, including metal oxides, hydroxyapatite (HAP), and, in particular, supported metal catalysts, is reviewed herein. The structure–activity relationships of catalysts and underlying reaction mechanisms are critically examined, and future research directions on the design and improvement of catalysts are also proposed.