【作者】 刘勇；

【导师】 朱文；

【作者基本信息】 华中科技大学 ， 材料工程， 2012， 硕士

【摘要】 利用太阳能光分解水制氢是未来彻底解决能源危机的理想途径之一，其中关键环节是开发出稳定、高效和廉价的光催化剂。1972年，Fujishima和Honda首次报道采用n型TiO₂半导体光阳极进行光催化分解水制取氢气之后，TiO₂纳米材料因其潜在的多方面应用受到人们更多的关注。在所有TiO₂纳米结构的材料中，金属钛片上制备出的垂直导向的TiO₂纳米管阵列因其有较大的比表面积和较强的吸附能力，在光催化分解水上的应用变得非常普遍。然而，TiO₂纳米材料光响应范围窄和量子效率低严重限制了其广泛应用。本论文在垂直排列、管口规整的TiO₂纳米管的管壁上外延生长出窄带隙化合物半导体CdSe，形成良好的同轴异质结结构，同时探究了同轴异质结薄膜电极的光电化学性质，取得了一些成果。采用两步阳极氧化法，将金属钛片置于H2O+NH4F+乙二醇的电解质体系中，制备出管口规整的TiO₂纳米管阵列。FE-SEM和XRD分析结果表明，在随后的第二步阳极氧化过程中，第一步阳极氧化生成的混晶型的氧化膜充当保护层，能有效减少下端纳米管顶部的崩裂。研究了TiO₂纳米管阵列衬底上镉和硒的欠电位沉积电化学行为。结合欠电位沉积技术和共沉积技术，优选出合适的沉积电位，以此为依据在高度规整有序的TiO₂纳米管管壁上外延生长窄带隙化合物半导体CdSe。FE-SEM、XRD、EDAX、TEM综合检测结果表明，已成功地在纳米管外壁制备出具有准化学计量比的CdSe外延层，获得了CdSe/TiO₂纳米管阵列同轴异质结结构。通过UV-vis漫反射谱对比测试表明，在引入外延层CdSe之后，TiO₂纳米管阵列薄膜具有良好的可见光响应性能。在合适的沉积电位下，通过改变沉积时间来调节外延层的厚度。对制备的CdSe/TiO₂/Ti样品进行了光电性能测试，结果表明当沉积时间为7h时制备得到的样品最大光电效率最高（6.45%），几乎是纯TiO₂纳米管阵列薄膜最大光电效率的5倍。当沉积时间进一步增长后，其光电转化效率却开始出现下降，可能是因为过多的外延层的量导致样品吸光面积急剧下降，光活性受到影响。此外，实验还对比研究了不同退火气氛对于样品光活性的影响，表明在氮气中退火能在TiO₂晶格中引入N原子，有利于光敏性的提高，但是提高幅度随着CdSe沉积时间增大而下降。本文最后尝试对同轴异质结结构进行Cu掺杂，发现TiO₂/CdSe/Cu/CdSe夹层结构相对于其他结构的光电活性更佳。对比发现，当Cu单次沉积电量为0.6C时光电性能最佳，最大光电转化效率达到14.20%。更多还原

【Abstract】 The photoinduced water splitting to produce hydrogen by utilizing solar energyeffectively, is considered to be an ideal way to solve energy crisis thoroughly in the future.The key segment is to develop a stable, efficient and inexpensive photocatalyst.In1972, Fujishima and Honda firstly reported the use of n-type TiO₂semiconductorphotoanode for photocatalytic water splitting. Since then, the TiO₂nanomaterials havebecome more and more attractive for their potential versatile application. Among all of theTiO₂nanostructured materials, vertically oriented TiO₂nanotubes （NTs） prepared on a Tifoil tend to be exceedingly popular in the application of photoinduced water splitting onaccount of their high specific surface area and excellent surface adsorption capability.However, due to their limited optical absorption and low quantum efficiency, theirwidespread use was severe limited.In this paper， CdSe, a kind of narrowband gap semiconductor compound, issuccessfully deposited onto the walls of the highly defined and ordered top-opening TiO₂nanotube array. Photoelectrochemistry properties of resulted film electrodes werediscussed and some results were achieved.A two-step anodization method was developed to obtain highly defined and orderedtop-opening TiO₂nanotube array in the electrolyte systems which contain H2O, NH4F andethylene glycol. Analysis results of FE-SEM and XRD indicate that the mixedcrystal-type oxide layers act as protective layers in the subsequent tube growth process,which can efficiently eliminate the undesired disintegration of the top end of nanotubesThe under-potential deposition （UPD） of Cd and Se elements on TiO₂nanotubesarray substrate was studied. CdSe, a kind of narrowband gap semiconductor compound, issuccessfully deposited onto the walls of the highly structured and orderly TiO₂nanotubesarray using a combination of UPD and co-deposition at a suitable potential. FESEM，XRD，EDAX and TEM analyses show that CdSe/TiO₂nanotube arrays with coaxialheterojunction structure have been formed.Contrastive analysis of the UV-vis diffuse spectrum showed that the resulted film hadgood visible response performance after the introduction of epitaxial layer CdSe onto the walls of TiO₂nanotube arrays.The thickness of the epitaxial layer was adjusted through changing the deposit time ata suitable potential. The photoelectrochemical properties of the resulted films with theCdSe/TiO₂nanotube-array coaxial heterojunction were discussed. The results show thatthe maximum photoconversion efficiency （6.45%）, almost a5-fold enhancement inphotoelectric activity comparedto that of a pure TiO₂nanotube array film,can be obtainedfor the sample with the sensitization layer using the deposition time of7h. However, itwas found in this study that as the deposition time increased, the photoconversioneffciency of corresponding sample abnormally minished. The reducedphotoelectrochemical performance of sample deposited CdSe for9h can be attributed to adecrease of surface area of the NTs for harvesting light.In addition, the effect of annealing atmosphere on the photoactivity of as-preparedsamples was also investigated. It suggested that the annealing in nitrogen atmospherecould introduce the N atoms to TiO₂lattice to a certain extent, which was conducive to theimprovement of photoactivity. However, the efficacy tended to decline as increasing thedeposition time.The modification through the Cu doping to coaxial heterojunction structure wastentatively performed at the end of experiment.It was found that sandwich structure ofTiO₂/CdSe/Cu/CdSe could achieve a better photoelectric activity compared to otherstructures. The maximum photoconversion efficiency reached14.20%when the Cudepsition charge was0.6C.更多还原