Fabrication And Photoelectrochemical Properties Of One-dimensional Self-organized NiO_x-doped TiO₂Nanotubes

In recent years, the performances of functional materials and devices weregreatly improved by the introduction of the nanomaterials. TiO₂have the dualfunctions of energy conversion by using solar energy and degradating pollutants inenvironment. Therefore, TiO₂nanomaterials are widely used in solar cell,electrochromic devices, photocatalysis, electrochemical energy storage, drugrelease and so on.However, as we known TiO₂is a wide band gap semiconductor with bandgapof3.2eV-3.4eV. Only ultraviolet light of sunlight can be absorbed, which limits thefully use of solar light. One-dimensional nanostructures with fast electron transferchannel and large specific surface area, exhibit more and more advantages in theapplications of physics, chemistry and biology. In this thesis, in order to modifyTiO₂energy band structure and improve the electronic transport performance, wefabricated one-dimensional self-organized Ni doped TiO₂nanotube arrays byelectrochemical anodization method. The details were shown as following:To grow self-ordered nanotubes, Ti–Ni alloys were used as the workingelectrode during electrochemical anodiztion process in ethylene glycol electrolytecontained F-. The doping concentration of Ni can be controlled by changing thecontent of Ni in the alloy （Ni contents of wt%,1wt%,2wt%,5wt%,50.8wt%）. Weexplored the effects of morphology of nanotube layers by change the experimentalparameters, such as anodic voltage, anodization time and Ni doping concentration.After annealing at different temperature, NiO_x-TiO₂nanotubes werecharacterized by means of SEM, XRD and XPS to obtain the information of surfacemorphology, crystallization and chemical compostion. The results domenstrated thatthe nanotube structure can be maintained at high temperature and the main valancestate of Ni element in TiO₂nanotubes is Ni²⁺and Ni³⁺.In order to further investigate NiO_xdoping effects on electrochemicalproperties of TiO₂,5%NiO_xdoped TiO₂nanotubes were studied by cyclicvoltammetry （CV）, electrochemical impedance spectroscopy （EIS） andMott-Schottky measurement. As expected, Ni doped TiO₂nanotubes show asignifancent enhancement in OH-intercalation ability, electrical conductivity anddonor concentration.To gain a better understanding of effect of Ni doping on kinetics ofphoto-generated charges transfer and photoresponse in visible range, surfacephotovoltage （SPV） measurements were performed. The results showed that the photoresponse of TiO₂nanotube was successfully extended to visible light range byNi doping. In addition, after annealing at proper temperature, the separationefficiency of photoinduced electrons-hole pairs was improved. These results willprovide theoretical basis for nanomaterials application in photoelectrochemistry.