Sm～(3+) Doped And Dye Sensitized Nanometer TiO₂ Film Electrodes For Photoelectrocatalytic Oxidation Of Methanol

Among the large number of nanostructured metal oxide semiconductors applied to the research of photocatalysis and solar cell field, nanometer TiO₂ is regarded as the most attractive material. But the absorption band of TiO₂ is only limited in ultraviolet region, which hinders its practical application. How to improve the conversion efficiency of light energy to electric energy becomes the research hotspot. Among various kinds of ways to modify the surface of the catalyst, metal ion doping and (or) dye sensitization of nanometer TiO₂ film electrode receive more and more attention. Study on the photoeletrocatalytic behavior and mechanism of metal ion doped and (or) dye sensitized nanometer TiO₂ film electrode are informative to the increase of the photoelectricity conversion efficiency. In this paper, Sm³⁺ doped nanometer TiO₂ film electrodes sensitized by RuL₂(SCN)₂:2TBA dye(where L=2,2 -bipyridyl-4,4 -dicarboxylicacid;TBA=tetrabutylammonium) have been prepared by improved sol-gel method and applied to photoelectrocatalytic oxidation of methanol. The activities of photoelectrooxidation of methanol and electrode/solution interface structure have been characterized by SEM, XRD, UV-vis, CV(single scan voltammetry) and EIS( electrochemical impedance spectrum). The main content is as follows.1. Sm³⁺ doped TiO₂ film electrodes have been prepared with different concentration and different calcining heat for the photoelectrooxidation of methanol. XRD SEM and CV characterization show that many factors including quantity of ion doped ,calcining heat ,uniformity degree of electrode surface , particle diameter and etc. have an important impact on the activity of photoelectrocatalytic oxidation of methanol. Under present condition,0.6% [n(Sm³⁺)/n(Ti02)] doping and 450°C calcining are the optimum process parameters.2.Methanol photoelectrooxidation activities of RuL₂(SCN)₂:2TBA sensitized and(or) ion doped TiO₂ film electrodes have been researched by CV and transient photocurrent response. The electronic coupling is established between dye and TiO₂ film through the interaction of absorbing functional radical of dye and TiO₂ film. So electrons are injected to the conductive band of TiO₂ electrode from excited state of dye , which extends the rangeof wavelength exciting T1O2 and enhances the efficiency of photoelectricity conversion. This implies that the synergistic effect exists between sensitizer and doped ion.3.The behavior of the electrode for photoelectrooxidation of methanol has been studyed in different methanol concentrations and in different pH values by CV. The results show that methanol is adsorbed to the electrode surface and then is oxidated. Electrode reaction begins with an activation process. The oxidated methanol concentration has a maximum, which verifies that the photoelectrooxidation of methanol involves adsorbing process . Compared with H2O, OH has priority to be absorbed on the surface of the TiC>2 electrode ,and is easily turned into ? OH .Thus, the photocurrent and corresponding maximum concentration of methanol are bigger in the alkaline solution than in the neutral solution or in the acid solution.4. The electrode/solution interface structure of Sm + doped and dye sensitized TiO2 film electrodes has been investigated by EIS. The relative parameters have been acquired. The flat band potential of ion doped TiO2 electrode sensitized by dye changes towards more negative potential. The density of holes on electrode surface increases. As a result, the photoelectrocatalytic activity improves. Measurement of electrode/solution interface structure parameters of ion doped and (or) dye sensitized TiO2 electrodes can be informative to explain the mechanism and the electric charge transmission property.This project is financially supported by the Natural Science Foundation of Hebei Province (No. 202351).