【作者】 陈达；

【导师】 李景虹；

【作者基本信息】 中国科学技术大学 ， 分析化学， 2008， 博士

【摘要】 近年来,人类目前所面临的这些能源危机和环境污染问题的日益突出,社会的发展要求开发出高效,无污染的清洁能源,支撑人类生存和发展的能源正从以石油,煤等为主的污染消费型能源转向清洁再生型能源。光电化学技术以其室温深度反应和可直接利用太阳能作为光源来驱动反应等独特性能,而成为一种理想的环境污染治理技术和洁净能源生产技术。其中,半导体纳米材料尤其是TiO₂纳米材料由于具有独特的光电化学性能、优异的热稳定性、生物惰性、无毒无害及制作简便等,使得它无论是在太阳能光电转换方面,还是在废物的降解处理方面都有很好的实际应用前景。然而,纳米TiO₂本身也存在诸多问题,比如:禁带宽,产生的电子—空穴对寿命短且极易复合,光谱响应范围较窄,这些都很大程度上抑制了纳米TiO₂的光电化学活性及其应用。针对目前纳米TiO₂存在的这些缺陷,本论文采用染料敏化、半导体复合、纳米电极有序构建以及新型电解质设计等途径对纳米TiO₂光电化学体系进行改性和优化,利用TEM、SEM、XRD和UV-vis等技术对这些TiO₂体系的微观结构和形貌进行了分析,并采用电化学阻抗谱（EIS）、Mott-Schottky谱（MS）、光电流谱以及光催化活性测试等手段测试其光电化学性能,对其相应的光电化学反应机理也进行了一定程度上的探索,为实现如何改善和控制纳米TiO₂（复合）体系的光电化学性能提供了重要的理论和实践参考价值。本论文主要开展了以下几方面的研究工作:1.利用静电层层自组装（LbL）技术,我们将卟吩染料分子和纳米TiO₂组装到FTO导电玻璃表面上,成功构建得到了有机染料/TiO₂纳米颗粒的有序复合薄膜,为染料敏化纳米TiO₂电极的有序化构建提供了新思路。光电化学测试结果表明,由于TiO₂复合薄膜中染料分子的光敏作用和膜层的线性有序组装,导致了该TiO₂复合薄膜体系不仅在紫外和可见光区域都出现了光电流响应,而且光电流的大小与膜层层数之间具有较好的线性关系。本论文的研究结果为如何有效改善和控制纳米TiO₂的光电化学性能提供了一种新方法,具有重要的研究意义。2.对准固态染料敏化TiO₂纳米晶太阳能电池（DSSCs）而言,电解液的组成与性能至关重要,影响到准固态DSSCs的光电转化效率和长期稳定性。目前,通常采用的聚合物电解液都不具备良好的离子导电性能,严重影响了准固态DSSCs的性能。针对目前准固态DSSCs中聚合物电解液离子导电性能较差的特点,我们在聚合物电解液的聚合过程中引入具有高离子导电性能的离子液体（BMlmPF₆,1-丁基-3-甲基-咪唑六氟磷酸盐）和杂多酸（PWA,磷钨酸）,成功合成得到了含有离子液体和杂多酸的聚合物复合电解液,实现了对聚合物电解液离子导电性的大幅改善,为新型聚合物电解液合成技术的探索提供了新的思路和途径。测试结果表明,在聚合物电解液中引入离子液体和杂多酸后,聚合物电解液的离子导电性大大提高;采用该聚合物复合电解液构建的准固态DSSCs电池的光电化学性能也在很大程度上得到了改善。本论文为纳米TiO₂光电化学体系提供一种新型聚合物电解质的同时,也为新型高效长期稳定的准固态DSSCs的构建及其可能应用提供了实验依据和重要参考价值。3.如何实现对纳米TiO₂体系的光电化学性能进行有效调控,一直是科研工作者们关注和研究的热点之一。本论文设计了一种制备纳米TiO₂图案化阵列电极的新型方法,并通过调控其相应的图案尺寸的方式发展和建立了一种简便有效控制纳米TiO₂体系光电化学性能的新途径。纳米TiO₂图案化阵列是基于传统光刻技术—微接触法（μCP）并结合热处理氧化法制备得到的,将作为“墨汁”的TiO₂前驱体溶液通过作为“印章”的图案化PDMS软模具压印复制转移到经过预处理过的FTO导电玻璃表面,得到图案化TiO₂前驱体阵列,再经热处理氧化后,即可制备得到有序规整排列的纳米TiO₂图案化阵列。采用这种方法来制备的纳米TiO₂图案化阵列具有许多重要的特性和优点,例如制备过程简便、成本低廉、快速、反应条件相对温和、结晶性能好而且图案化尺寸调控方便易行等。光电化学测试结果表明,不同特征尺寸的图案化纳米TiO₂阵列具有明显不同的光电流响应和光催化活性,随着图案尺寸的减小,其相应的光电化学性能则相应的增加;由此,通过控制纳米TiO₂图案化阵列中图案特征尺寸的大小,可以有效地调控纳米TiO₂阵列的光电化学性能。本论文的研究结果对有序化半导体纳米电极表面的构建及其光电化学性能的有效调控都具有积极而重要的参考价值和指导意义。4.半导体复合是纳米TiO₂改性的重要途径之一,然而通常的复合方式大多集中在纳米颗粒之间或一维纳米材料之间,而对（零维）纳米颗粒与（一维）纳米棒间的复合研究很少。本论文通过简便温和的水热法,一步合成制备得到了TiO₂纳米颗粒/ZnO纳米棒的半导体复合纳米材料。通过调节前驱体中Ti/Zn的摩尔比,就可以实现对TiO₂/ZnO纳米复合材料形貌的有效调控。光电化学测试结果表明,相对于单纯的TiO₂纳米颗粒或ZnO纳米棒而言,TiO₂/ZnO纳米复合材料的光谱响应范围明显的增加,而且光电流和光催化活性都大大地改善了。这是因为,TiO₂纳米颗粒与ZnO纳米棒进行复合后,在TiO₂/ZnO界面形成了异质结,有效地促进了光生电荷的分离,增加了光谱响应范围,同时增大了半导体材料的比表面积,从而很大程度上改善了其相应的光电化学性能。本论文为纳米TiO₂光电化学性能的改善提供了一种新的思路和手段,在一定程度上丰富了合成新型半导体纳米复合材料的内容,具有重要的科学意义和参考价值。更多还原

【Abstract】 Recently,in response to the increasing demands for solving the energy crisis and environment pollution,which severely threaten the human’s survival, considerable efforts in this aspect have to be directly connected with a challenging search for new clean and regenerative energy sources with high efficiencies and no pollution to replace the pollutive and consumptive energy sources such as petroleum and coal.It is generally accepted that breakthroughs in photoelectrochemical technologies hold the key to new generations of the direct solar energy-based photovoltaic cells,not only for applications in providing clean and regenerative energy but especially for eliminating environmental pollution.To date,due to their unique photoelectrochemical properties,excellent chemical stability,bioinertness, innocuity and easy preparation,semiconductor nanomaterials especially TiO₂ nanomaterials have been widely used in the photoelectrochemical fields such as solar photo-electric conversion and photocatalytic treatment of the pollutants.However,TiO₂ nanomaterials still have several drawbacks,such as wide bandgap,short-lifetime and easy recombination of the photogenerated electron-hole pairs and the limited photoresponding range,which to a great extent hinder their photoelectrochemical activities as well as their applications. In this dissertation,pursuing these efforts towards improving the photoresponding range and the photoelectrochemical activities of TiO₂ nanomaterials,we have explored the feasibility to design and optimize the nano-TiO₂ architectures for potential photoelectrochemical applications by means of dye-sensitization,semiconductor hybridization,fabrication of ordered surface,utilization of novel electrolytes,and so on,which were characterized by TEM,SEM,XRD and UV-vis measurements.Their photoelectrochemical performances have been evaluated by means of various techniques including electrochemical impedance spectroscopy（EIS）,Mott-Schottky（MS） spectroscopy,photocurrent and photocatalytic measurements,and the corresponding photoelectrochemical mechanisms were to some extent investigated.It is expected that the research work in this dissertation can provide useful and important theoretical and practical guidances for the effective enhancement and control of photoelectrochemical performances of nano-TiO₂ architectures.The main contents in this work are listed in the following:1.The stepwise assembly of negatively charged dye molecules and positively charged TiO₂ colloids on pretreated fluorin-dopped tin oxide（FTO） conductive glass substrate surfaces utilizing the layer-by-layer（LbL）approach was successfully fabricated,which was characterized by UV-vis spectrophotometry and electrochemistry.Photocurrent measurements demonstrated that the photocurrent response within the UV and visible wavelength range were observed in these hybrid thin films,and the generated photocurrent increased linearly as the deposited bilayers increased,which could be attributed to the dye-sensitized effect of the layered dye molecules and the linearly ordered assembly of hybrid thin films.It was demonstrated that electrostatic LbL films were attractive systems for the photoelectrochemical investigation,and the effective control of the photoelectrochemical performances of nano-TiO₂ architectures could be achieved by the structure of the multilayered films.2.Growing attention has been paid to quasi-solid dye-sensitized solar cells（DSSCs）using polymer gel electrolytes due to their unique hybrid network structure and favorable properties such as thermal stability, non-flammability,negligible vapor pressure and easy solidification,when compared with the liquid electrolytes.To pursue high conversion efficiency of DSSCs,it is necessary and pivotal to enhance the ionic conductivities of these polymer gel electrolytes.However,conventional polymer electrolytes exhibit very low ambient ionic conductivity because of the severe crystallinity of polymers.In this respect,a novel composite polymeric gel comprising room-temperature ionic liquids（1-butyl-3-methyl-imidazoliumhexafluorophosphate, BMImPF₆）and heteropolyacids（phosphotungstic acid, PWA）in polymer matrix was successfully prepared and employed as a quasi-solid state electrolyte in DSSCs.These composite polymer electrolytes offered specific benefits over the ionic liquids,and heteropolyacids,which effectively enhanced the ionic conductivity of the composite polymer electrolyte.The performances of the unsealed DSSCs employing these composite polymer electrolytes were also enhanced to a great extent.It is expected that these composite polymer electrolytes are new attractive alternative electrolytes for the fabrication of the long-term stable quasi-solid state or solid state DSSCs.3.In efforts to make use of unprecedented physical and chemical characteristics of TiO₂ nanomaterials and effectively control their unique photoelectrochemical properties,it is essential to affix them on surfaces or arrange them in an organized network.In this work,patterned TiO₂ microarrays with different features were successfully fabricated by using a simple,fast and cheap patterning technique,and their photoelectrochemical performances could be adjusted by the control of the feature size of TiO₂ patterns.As an alternative to typical pattern transfer techniques for microfabrication,this work employed a standard microcontact printing（μCP） process for the fabrication of patterned TiO₂ microarrays onto FTO substrates. During theμCP process,the TiO₂ precursor was used as the "ink" and transferred from a pattern-featured poly（dimethylsiloxane）（PDMS）"stamp" onto the pretreated FTO substrate.Following the subsequent thermal oxidation,patterned TiO₂ microarrays with different features were successfully achieved.It was demonstrated that their photoelectrochemical properties were dependent on the feature size of the TiO₂ patterns.With the decrease of the feature size,the photocurrent activity and photocatalytic ability of the patterned TiO₂ thin film increased,which was due to the increased TiO₂ surface area as well as the increased optical path length within the patterned TiO₂ thin film, resulting from multiple reflection of incident light.This work indicates that patterned TiO₂ thin films are attractive systems for surface tailoring and also provide a novel method to effectively control the photoelectrochemical properties of nanostructured TiO₂ thin films with promising applications in microsystem devices for solar energy conversion,photocatalysis,sensing,and SO on,4.In order to enhance the photogenerated charge separation and the photoresponding range of nano-TiO₂,considerable interest has focused on TiO₂-based nanocomposite.Generally,there has been considerable effort made toward the investigation of nanocomposites comprising zero-dimensional（1D）nanoparticles or one-dimensional（1D）nanostructures; however,to the best of our knowledge,little attention has been paid to the coupling of 1D nanostructures with 0D nanoparticles.In this work,novel coupled bicomponent nanocomposites consisting of anatase TiO₂ nanoparticles and wurtzite ZnO nanorods were successfully prepared using a one-step hydrothermal method for the first time,and their structures and morphologies could be controlled by adjusting the Ti/Zn molar ratio of the precursors.Compared with the mere TiO₂ nanoparticles or ZnO nanorods,the coupling of TiO₂ nanoparticles and ZnO nanorods produced a significant effect on its properties,such as surface morphologies,surface areas,electronic properties,and photoelectrochemical properties.The generated photocurrent of the coupled ZnO-TiO₂ nanocomposite was largely enhanced with several orders of magnitude higher intensities than that of the mere TiO₂ nanoparticles or ZnO nanorods.The photocatalytic activities of the coupled TiO₂-ZnO nanocomposites were also significantly enhanced.The enhancement of the photocurrent actions and photocatalytic activities might arise from the increased surface area,which can enhance the light harvest and the ability of generating photoinduced electron-hole pairs of active sites,and the favorable electron-transfer properties of the heterojunctions TiO₂/ZnO in the coupled ZnO-TiO₂ nanocomposites.It is expected that the present work is of notable significance for understanding the unique properties that result from the coupled nanocomposites and designing new nanocomposites with advanced functions in photoelectrochemical applications.更多还原