聚合物介导自组装构建新型二氧化钛基高效光电解水阳极的研究

发布时间：2018-04-16 15:11

本文选题：光电催化 + 二氧化钛纳米线阵列　；参考：《西南大学》2017年硕士论文

【摘要】：进入21世纪以来,日益枯竭的能源储备和日渐严峻的环境污染是世界各国人民所要面临的两大挑战。由于太阳能资源丰富并且清洁无污染,因此人们对于探索利用太阳能的步伐从来都没有停止过。通过水裂解将太阳能转化为氢气形式的化学能可能是解决当今能源和环境危机的终极策略。光电化学(PEC)水分解是太阳能水分解中一种非常有潜力的方式,因为它的成本低、效率高、清洁环保且具有可工业化生产的潜能等优点。然而,其性能受到非常缓慢的水氧化反应的限制。因此,大量研究集中于改善催化水氧化反应的光阳极。在各种光阳极材料中,二氧化钛(TiO_2)由于其有利的能带边缘位置、强的光学吸收、优异的化学稳定性、耐光腐蚀性以及低成本受到了广泛关注。然而,TiO_2的STH效率在本质上受其大的禁带宽度和快速电子-空穴复合的限制。一方面,大量的研究集中于增强宽带隙金属氧化物半导体的可见光吸收。例如,利用窄禁带半导体的敏化或通过元素掺杂使带隙变窄是两种普遍使用的方法,以达到改变金属氧化物光电极的光吸收系数和吸收波长范围从而改善金属氧化物光电极的转换效率。另一方面,同样重要的是从根本上改善TiO_2的形貌和电子结构以有效分离和传递光生载流子。本论文将分别采用Cu_2O和CoO_x对TiO_2纳米线阵列光电极进行表面修饰,所形成的复合异质结均有效地提高了纳米线阵列的光电解水性能,并进一步探讨了材料的合成机理以及光生载流子在这些异质结光电极中的转移机理。本论文具体内容分为三个部分:1.我国2016年的能源生产消耗现状,表明了清洁能源研发生产的重要性,简要回顾了光解水、光催化剂以及PEC光催化系统的发展和目前所面临的困境,系统介绍了二氧化钛用于光解水体系的现状,二氧化钛的晶体结构、能带结构和催化机制,以及提升二氧化钛在PEC系统中催化活性的途径。自组装在构建纳米材料方面有着广阔的应用前景,特别是在模板上利用自组装的方式构建纳米级复合材料,主要介绍了在软模板如小分子、线性聚合物、生物分子等和硬模板如碳纳米管上的自组装,而后介绍了影响自组装的几大因素,最后介绍了本论文所涉及实验的实验用品,材料表征方法及电化学性能测试方法。2.聚合物介导自组装的TiO_2@Cu_2O核壳纳米线阵列用于高效光电化学水氧化。我们利用新型、简便、经济以及易于工业化生产的聚合物调节自组装的方法在TiO_2纳米线阵列(NWA)上有规律地生长Cu_2O的超薄连续薄层以形成真正的核壳结构TiO_2@Cu_2O NWA光电极,在此过程中聚合物作为稳定剂、还原剂和连接剂。将该异质结直接作为PEC水分解的光阳极,在0.5 M Na_2SO_4溶液中显示出(在相对于RHE为1.23 V时)的光电流密度为4.66 mA cm~(-2),最大光转化效率为0.71%,两者都是在相同条件(中性条件和没有任何牺牲剂)下以TiO_2作基底的光阳极测量报道的最高值。TiO_2@Cu_2O NWA对水氧化优异的PEC性能主要是由于它大大增强了电极对可见光的吸收并促进了电荷分离使得光生载流子密度增大、转移和传递速度增加。这项工作不仅制备了一种新颖的TiO_2@Cu_2O核壳NWA光阳极材料用于高效PEC水氧化过程,并深入研究了其增强机制,科学探讨了聚合物调节的自组装合成材料的机理,使其能拓展应用到制造各种其他的核-壳纳米架构。3.聚合物调节自组装CoO_x纳米颗粒于TiO_2纳米线阵列上显著促进光电化学水氧化过程。助催化剂在以TiO_2为基底的光阳极的光电化学(PEC)水分解性能改进上起着重要的作用,但它的合成和组装仍面临着很大的挑战。在这个工作中,我们研究了在TiO_2 NWA上通过聚合物调节自组装的方式直接生长超小尺寸、均匀分散和高度密集的CoO_x NP_s,聚合物使CoO_x NP_s强烈地与TiO_2相互作用,这有效地稳定了纳米线阵列上的CoO_x NP_s及其前驱体,并在高温水热条件下可靠地还原Co~(2+)。将制得的杂化纳米阵列作为PEC水氧化的光电极,其中CoO_x NP_s作为TiO_2 NWA的助催化剂,测得的光电流密度为1.67 mA cm~(-2),光转化效率为0.79%,这分别为纯TiO_2 NWA(0.54 mA cm~(-2),0.30%)的3.02倍和2.63倍,均高于已报道的在相同条件下发生水氧化的助催化剂修饰的TiO_2光阳极的最大值。此外,其光电流密度在6900 s衰减?11.81%,而纯TiO_2 NWA衰减为54.40%。CoO_x NP_s显著的助催化效应归因于其高的自身催化活性、超小的尺寸、良好的分散、高的组装密度以及其结构的稳定带来的明显增强的电荷分离、转移、传输和减少的载流子复合。这项工作创造了一个新的CoO_x NP_s/TiO_2 NWA光电极,它显著地提高了TiO_2 NWA的PEC水氧化性能,另外我们深入地研究了其增强机制,并提供了一个可广泛应用的自组装各种纳米结构光电极的方法。
[Abstract]:Since twenty-first Century, the increasing depletion of energy reserves and the increasingly serious environmental pollution are two major challenges faced by the people all over the world. Because of abundant solar energy resources and clean, so people for exploring the use of solar energy the pace never stopped. By water splitting to convert solar energy into chemical energy may be in the form of hydrogen the ultimate strategy to solve the energy and environmental crisis. Photoelectrochemical (PEC) water decomposition is a promising way of solar water decomposition, because of its low cost, high efficiency, environmental protection and clean industrial production has potential advantages. However, its performance is very slow water oxidation reaction limit light anode. Therefore, many researchers focused on improving water catalytic oxidation. In the light of various anode materials, titanium dioxide (TiO_2) due to its favorable band edge position The strong optical absorption, excellent chemical stability, corrosion resistance and low cost has attracted widespread attention. However, the efficiency of TiO_2 STH by its large band gap and fast electron hole recombination restriction in nature. On the one hand, a large number of studies have focused on enhancement of wide band gap metal oxide semiconductor visible light absorption. For example, the use of narrow gap semiconductor or sensitized by element doping is the two methods commonly used to achieve the change of band gap narrowing, metal oxide photoelectrode light absorption coefficient and wavelength range so as to improve the efficiency of the photoelectric conversion of metal oxide. On the other hand, it is also important to improve the morphology and electronic structure TiO_2 to transfer and effective separation of photogenerated carriers from the root. This paper uses Cu_2O and CoO_x arrays of TiO_2 nanowires photoelectrode surface modification, the formation of the complex He heterojunction effectively raised photoelectric nano wire array solution of water resistance, and further explore the mechanism of synthesis of materials and photo carrier node transfer mechanism in the heterogeneous photo electrode. The main contents of this thesis is divided into three parts: energy production and consumption status of China in 2016 1., shows the importance of clean the energy research and development production, a brief review of the water splitting photocatalyst and photocatalytic PEC system development and are currently facing difficulties, introduces the present situation of the application of titanium dioxide photolysis of water system, the crystal structure of TiO2, the band structure and catalytic mechanism, and the way to enhance the catalytic activity of TiO2 in the PEC system. Self assembly in the construction of nano materials have broad application prospects, especially in the template by self-assembly method to build nano composite materials, mainly introduced in the soft template such as Small molecules, biological molecules and linear polymers, such as hard template self-assembly of carbon nanotubes, and then introduces some factors affecting the self-assembly, finally introduces the activities involved in this paper experiment, test method of material characterization and electrochemical properties of TiO_2@Cu_2O core-shell nanowires.2. polymer mediated self-assembly of array for efficient photoelectrochemical water oxidation. We use a new type, simple, economic and easy industrialized production method to adjust the polymer self-assembled nanowire arrays on TiO_2 (NWA) on the regular growth of Cu_2O thin continuous thin layer to form core-shell structure TiO_2@Cu_2O NWA photoelectrode real, in the process of polymer as stabilizer, reduction agent and connection agent. The heterojunction directly as light anode PEC water decomposition, shown in 0.5 M Na_2SO_4 solution (with respect to RHE for 1.23 V) of the photoelectric current. For 4.66 mA cm~ (-2), the maximum conversion efficiency of 0.71%, both of which are in the same conditions (neutral condition and no sacrificial agent) with TiO_2 as anode substrate measurements reported the highest.TiO_2@Cu_2O NWA on the performance of PEC water is mainly due to its excellent oxidation greatly enhances the absorption of visible electrode light and promote charge separation of the light induced carriers density increases, transfer speed increases. This work not only the preparation of a novel TiO_2@Cu_2O core-shell NWA photo anode materials for efficient PEC water oxidation process, and in-depth study of the mechanism of the enhanced science, discussed the mechanism of self-assembly synthesis of polymer materials regulation the so that it can be applied to manufacture all kinds of other core-shell structure polymer.3. regulation of self-assembled CoO_x nanoparticles in the TiO_2 nanowire array significantly promote the photoelectrochemical water oxidation process. The catalyst as the anode of Photoelectrochemical substrate in TiO_2 (PEC) decomposition of water plays an important role to the performance improvement, but the synthesis and assembly of it is still facing great challenges. In this work, we studied in TiO_2 NWA by adjusting polymer self-assembly approach direct growth of ultra small size. The uniform dispersion and high concentration of CoO_x NP_s, CoO_x polymer NP_s strongly interacted with TiO_2, which effectively stabilizes the CoO_x NP_s and its precursor on nanowire arrays, and reliable reduction of Co~ in high temperature hydrothermal conditions (2+). The hybrid nano array prepared as photoelectrode of PEC water oxidation among them, CoO_x NP_s TiO_2 NWA as cocatalyst, the photocurrent density measured for 1.67 mA cm~ (-2), optical conversion efficiency was 0.79%, which were pure TiO_2 NWA (0.54 mA cm~ (-2), 0.30%) 3.02 times and 2.63 times, were higher than those reported The maximum value of TiO_2 anode catalyst modified water oxidation under the same conditions. In addition, the photocurrent density of 6900 s attenuation? 11.81%, pure TiO_2 NWA and its catalytic activity for catalytic 54.40%.CoO_x NP_s attenuation effect was attributed to its high, ultra small size, good dispersion. High density assembly and stable structure has significantly enhanced the charge separation, transfer, transmission and reduce the carrier recombination. This work has created a new CoO_x NP_s/TiO_2 NWA photoelectrode, it significantly improves the performance of PEC water oxidation of TiO_2 NWA, we also studied the mechanism of the enhanced and, to provide a widely used self assembled nano structure photoelectric electrode method.

【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O646;TQ116.21

【参考文献】