| The Energy shortage problem is presently playing a role of limitting the economic development of modern society, which has drawn a lot of attention from scientists and researchers in both academia and industry. With a huge consumption of coal, oil and other fossil fuel energy resources that are not generally renewable, human beings are in a great need of developing the novel renewable energy. Solar energy has many advantages including cleaness, high efficiency and high resource supply therefore has been one of the most promising renewable energy rescources. Among the multiple research projects on solar energy, the exploration of collecting, converting and making full use of this novel energy has attracted plenty of interests. TiO2is well-known for its abundant reserves, low price and good performance (such as environmental friendly, stable and durable), which makes it stand out of the numerous materials that are capable of absorbing solar energy and directly converting it for practical applications.TiO2nanotube arrays (TNTAs) prepared by anodic oxidation method has a very large specific surface area and excellent photoelectrochemical properties. In this paper, the research starts from changing the shapes of traditional TNTAs. After the two-step anodic oxidation method, some TiO2nano rings with large diameters assembled on the traditionally structured TNTAs and enhanced the photoelectrochemical properties. Based on the results obtained by adjusting the reaction voltage and time of the two-step anodic oxidation method, a trend of the influence on the performance of the electrodes is concluded, as well as a novel preparation method of TNTAs with a highly-ordered and controllable structure is reported.Due to the disadvantage of a wide band gap (anatase, Eg-3.2eV) besided advantages, TNTAs can only absorb and respond to the UV light of which the wavelength is shorter than380nm. This kind of light only covers no more than5%of the sunchine sourced to the surface of the earth, which hence leads to a result that most of the solar energy cannot be fully and effecticely utilized. The method of metal elements doping can form a new impurity level or even a new middle level and the band gap of TiO2can be narrowed and the excitation energy of the electron jumping can also be lowered by this method. It has been realized that the response to the visible light, the better use of solar energy, and the improvement of the photoelectric conversion efficiency can be accomplished. Some previous research has reported that the metal ions doping (such as Co, Fe) can greatly improve the photoelectrochemical properties of TNTAs. These results coincide with the conclusion of the theoretical calculation from our group members. Furthermore, Co and Fe are abundantly reserved, environmentally friendly, non-toxic, stable and cheap, boosting the utilization of them for doping TNTAs.Hierachical TiO2nanotube arrays (TNTAs) were prepared by a two-step anodic oxidation method. Then, Co-doped and Fe-doped hierachical TNTAs were prepared by a microwave assisted method, where ethylene glycol acted as the microwave dielectric. The samples were characterized by SEM, XRD, UV-vis diffuse reflectance spectra and electrochemical tests. The results show that the photoelectrical performance could be improved and the response to the visible light was achieved in the Co-doped and Fe-doped samples. Under visible light irradiation at10mW/cm2, the saturation photocurrent, photoconversion efficiency and carrier density of the optimized Co-doped sample were increased by18times,20times and5times, respectively, and the optimized Fe-doped sample were increased by7times,8times and11times, respectively, in comparison to the un-doped sample. These results show that the microwave-assisited doping technology is an easy and efficient experimental method which can effectively improve the photoelectical performance of TiO2nanotube arrays. |
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