One-dimensional TiO₂ And ?-Fe₂O₃ Photocatalysts For Photoelectrochemical Application

The major issue of 21 century is resource, environment, population and sustainable development of human society. The rapid development of economy in this century leads to large energy consuming and therefore, crisis of energy has become a serious problem needing to be addressed, though the traditional fossil fuel, including oil, natural gas and coal can meet our cuurent demand for energy. However, those fossil fuels are nonrenewable and closely associated with greenhouse, acid rain and the degradation of environment. Thus, it is greatly desired to find green and clean resource for maintaining economic development and reducing the negative effects on natural environment. Hydrogen, as a high efficiency and green energy, has attracted much attention of reseatchers.Photoelectrochemical water splitting has been known as a promising method to transform solar to hydrogen since Fujishima and Honda exploit Titanium dioxide as photocatalyst in 1972. In this technique, preparation of various semiconductors with unique morphology and advanced function as electrode are considered to be one of the main challenges for achieve high efficient photoelectrochemical water splitting. Among the semiconductors, TiO₂ and Fe₂O₃ are particularly concerned by researchers owing to their low cost and toxicity, highchemical and photochemical stability. The specific content of this paper is divided into the following three parts:Synthesizing PH₃-treated anatase TiO₂ nanorod films on transparent conducting substrate for improved photoelectrochemcial water splitting: In this work, we used hydrochloric acid?36.5 38 wt%?, concentrated sulfuric acid?98 wt%?, tetrabutyl titanate as raw materials, through a hydrothermal method to prepare the highly oriented, crystalline anatase TiO₂ nanowires on the transparent conducting substrate. Then, the anatase TiO₂ NWs samples were annealed by PH₃ at 300? for 1 h to prepare PH₃-treated anatase TiO₂ nanorod arrays. SEM, XRD, UV-vis, IPCE, UPS, I-V, Voc decay, IMPS measurements were used to characterize the samples and evaluate their photoelectrochemial performance. After testing, a greatly enhanced photocurrent of 0.4 mA/cm² can be achieved, which is two times higher than the untreated samples.Synthesizing PH₃-treated rutile TiO₂ nanorod films on transparent conducting substrate for improved photoelectrochemcial water splitting: Hydrothermal method was also used to prepare vertically aligned rutile TiO₂ nanorod arrays with reaction solution containing deionized water and hydrochloric acid?volume ratio 1:1? as well as 500 uL tetrabutyl titanate. Using the same method as above section for preparation of PH₃-treated anatase TiO₂ nanorod, PH₃-treated rutile TiO₂ can be also successfully synthesized. The morphology, electronic and photoelectrochemical properties of samples were characterized by SEM, XRD, UV-vis, IPCE, UPS, I-V, Voc decay and IMPS measurements. Surprisely, the largely improved photocurrent as high as 1.8 mA/cm² can be obtained for treated samples, which is 18 times higher than that for the prinstine rutile TiO₂ films?0.09 mA/cm²?.Preparation of Fe₂O₃ nanotubes: With the attempts for growing Fe₂O₃ nanotubes, iron sheets were anodized by the two-electrode system, with iron sheets as the anode and platinum plate as a counter electrode. The electrolyte for anodic oxidation is mainly composed of ethylene glycol, in which x wt% of NH₄F and y vol% of DI was added. SEM was used to characterize the morphology of samples. The parameters that influencing the morphology of samples, including temperature, the concentration of NH₄F, voltage and duration of reaction time, were discussed in detail. The photoelectrochemical performance of the samples were tested under illumination of AM 1.5G, with light intensity of 100 mW/cm².