【作者】 阴育新；

【导师】 靳正国；

【作者基本信息】 天津大学 ， 材料学， 2007， 博士

【摘要】 自Fujishima等发现TiO₂半导体光电极具有分解水的功能,纳米TiO₂光催化氧化技术作为一种制氢技术引起广泛重视。垂直于电极的TiO₂纳米管阵列具有高的光生电子传输效率,并且通过金属、非金属掺杂和与窄带半导体复合,可以提高TiO₂半导体光阳极对可见光的吸收,从而提高分解水的效率。本工作主要开展了电化学阳极氧化制备TiO₂纳米管阵列的研究,系统探讨了工艺参数对纳米管阵列生长的影响。另一方面在紫外和可见光下,研究了TiO₂纳米管阵列光电催化分解水的性能,通过对TiO₂纳米管阵列进行改性,明显提高了光电转换效率。主要研究结果和进展如下:1.HF水基电解液由于对TiO₂高的溶解速度限制了纳米管的生长,所以仅能得到长度小于500nm的阵列。采用NH4F/乙二醇/水体系电解液,制得的TiO₂纳米管阵列膜的厚度可达36μm,在含水量少、高的阳极氧化电压条件下,纳米管顶部沿管轴向垂直劈裂为直径20nm、长度达几微米的无定型TiO₂纳米线。2.在NH4F/甘油/水新体系电解液研究中,随着电解液pH值的减小,TiO₂纳米管的表面平整度增加,管底部的溶解速度增加。在碱性和加入缓蚀剂（HMT和NaAc）的电解液中,由于大大降低了电解液对管口处TiO₂的溶解速度,增加了纳米管的净生长速度。经550℃热处理、管结构完整、管径为60nm、长度为3.3μm的TiO₂纳米管阵列膜在强度为1.6mW/cm2紫外光的照射下,光电催化分解水的效率达23.8%。3.采用还原气氛热处理工艺,在TiO₂中引入氧缺位,提高了纳米管阵列对可见光的吸收,使光电解水的电流密度提高1倍。交流电沉积法制备的Pt/TiO₂纳米管阵列,在测试电压为–0.95V处（vs. Ag/AgCl）出现Pt2+催化峰;浸渍提拉法制备的Pt/TiO₂纳米管阵列,在测试电压为–0.95和–0.7V处（vs. Ag/AgCl）出现Pt2+和Pt0两个催化峰。4.首次采用交流电沉积技术制备了核/壳异质结型CdS@TiO₂纳米管阵列,沉积的CdS层经过400℃热处理1h后呈六方结构。在管径为150nm、长度为2.5μm的TiO₂纳米管阵列基底上,按照交流电压5V、沉积30min的工艺获得的光阳极,在可见光区具有较高的光电分解水的电流密度。更多还原

【Abstract】 Since the discovery of photoelectrochemical splitting of water into hydrogen and oxygen on n-TiO₂ electrodes, semiconductor-based photoelectrolysis of water has received much attention in hydrogen fuel. A variety of reports have indicated that the highly ordered vertically oriented nature of the crystalline TiO₂ nanotube （NT） arrays makes them excellent electron percolation pathways for vectorial charge transfer between interfaces. Furthermore, to increase water splitting efficiency, several attemps have been made to obtain a good visible light adsorption for n-TiO₂ NT arrays by metal and non-metal doping, combinainon with narrow-band gap semiconductor.In the present work, we focused on the development of electrochemical anodic oxidation technique to prepare self-organized TiO₂ NT arrays on titanium foil. The effects of the process parameters on the TiO₂ NT arrays growth were systemically studied. On the other hand, we examined the use of TiO₂ NT arrays as anode for the photocleavage of water under UV and Xe lamp irradiation, with particular emphasis on the enhancement of photoelectric efficiency by modifying the TiO₂ NT arrays, such as introducing vacancies in oxygen lattice sites, depositing Pt or CdS microcrystals onto TiO₂ NT. The main results and progresses of this dissertation are outlined as following:1. Highly density, well ordered and uniform TiO₂ NT arrays were fabricaed by electrochemical anodization of titanium sheets in the HF/water electrolyte. The results confirmed that the length of NT arrays was limited to 500nm due to high chemical dissolution rate of solution to the top of TiO₂ NT arrays. In NH4F/glycol electrolytes, the ordered TiO₂ NT arrays with lengths up to 36μm were achieved because of the low quality barrier layers through which ionic transport may be enhanced. We have demonstrated that TiO₂ nanowires with a diameter of 20nm and a length up to several micron only can be synthesized in NH4F/glycol solution with a small amount of water and high anodic voltage. The nanowires originated from the vertical splitting of anodically grown nanotubes.2. A new NH4F/glycerol system has been developed to prepare the controllable architecture of TiO₂ NT arrays. It was found that uniform surface morphology of the NT arrays was obtained in acidic condition. However, the basic and inhibitor （HMT and NaAc） added environments were much more efficient for relatively longer nanotubes by effectively slowing the chemical dissolution rate at the tube mouth. The TiO₂ NT arrays with 60nm inner pore diameter, 3.3μm length and 20nm wall-thickness, annealed at 550℃, behaved a remarkable water photoelectrolysis efficiency of 23.8% upon UV illumination at intensity of 1.6mW/cm2.3. Optical absorption spectra showed that TiO₂ NT arrays annealed under H2 atmosphere noticeably absorbed the light at visible light by introducing vacancies in oxygen lattice sites, whereas the TiO₂ NT arrays annealed under air and Ar atmosphere did not. So the TiO₂ NT arrays （H2） generated photocurrents double of what the others （air and Ar） sample do in the Xe illustration. Pt nanoparticles were successfully deposited on the surface of TiO₂ NT arrays by ac electrodeposition and dipping method. There was one catalytic peak of the electrodeposition electrode, which was at -0.95 V vs. Ag/AgCl attributed mainly to Pt2+ catalysis. There were two catalytic peaks of the dipped electrodes, one was at -0.95 V vs. Ag/AgCl attributed mainly to Pt2+ catalysis and the other was at -0.7 V vs. Ag/AgCl attributed to Pto catalysis.4. Furthermore, a novel fabrication route for core/sheath heterostructure CdS@TiO₂ NT arrays was proposed using ac electrodeposition for application in photoelectrochemical cells. The deposited material was found to be hexagonal CdS structure annealed at 400℃. The maximum photocurrent density was obtained with the core/sheath heterostructure CdS/TiO₂ nanotube arrays with 2.5μm tube length, which were fabricated by CdS deposition at 5 V for 30 min.更多还原