氧化物半导体异质结构的合成及光电化学分解水性能研究

发布时间：2018-09-07 21:27

【摘要】：由于化石燃料的不断锐减以及其给环境所带来的负面影响,致使研究者对于利用太阳能分解水制备氢能越来越有兴趣。太阳能裂解水制氢的推广应用需要降低催化剂的成本以及提高分解水效率。光电化学(PEC)分解水制氢综合利用太阳能和电能,这有利于提高分解水效率。为了进一步提高PEC分解水效率,需要提高光阳极对入射光的捕获能力、光生电荷的传输/分离能力以及光阳极表面的水氧化动力学过程。半导体异质结构作为PEC光阳极在提高电子传输、提高光捕获能力、提高表面反应效率等方面都非常有效。本文着重于异质氧化物半导体材料的合成以及在PEC分解水方面的应用,主要研究内容如下:(1)三维TiO2/ZnO异质结构的合成及PEC分解水性能研究。利用水热法在FTO基底上合成TiO2纳米棒阵列,然后以TiO2纳米棒阵列为基底修饰ZnO晶种,随后在ZnO的前驱液中进行水热反应得到三维TiO2/ZnO异质结构阵列。通过改变前驱液浓度、反应温度、反应时间调控三维TiO2/ZnO的形貌并研究对PEC活性的影响。实验结果表明硝酸锌的浓度为10m M,反应温度与时间分别为90oC和3h得到的三维TiO2/ZnO异质结构,在1.23 V vs RHE光电流能够达到1.13 mA/cm2(1.23 V vs RHE),是纯ZnO纳米棒(0.3 mA/cm2)的近四倍、纯TiO2(0.6 mA/cm2)的近二倍。与TiO2和ZnO光阳极相比,三维TiO2/ZnO异质结构的载流子密度及电子寿命均有明显提高。光吸收及动力学测试结果表明三维TiO2/ZnO异质结构有利于提高光阳极的光捕获能力、增强载流子密度及其电荷传输与分离效率,表现出优异的光电化学性能。(2)WO3/ZnO异质结构的合成及PEC分解水性能研究。首先通过化学浴法在FTO导电基板上生长ZnO纳米棒。研究了反应时间对ZnO薄膜形貌和性能的影响。根据光电化学测试结果,反应时间为3h制备的ZnO光阳极表现出较高的PEC性能。随后利用仲钨酸铵为原料,以ZnO纳米棒阵列为基底通过水热法合成了WO3/ZnO异质结构,并作为PEC分解水的光阳极。WO3/ZnO异质结构的光电流密度是1.225 mA/cm2(1.23 V vsRHE),是纯ZnO光阳极的两倍(0.508 mA/cm2)。通过Mott-Schottky和EIS证实WO3/ZnO异质结构光电流提高的原因在于WO3/ZnO异质结构扩宽了可见光响应、增加了载流子密度,另外界面处的电荷分离以及电荷传输也明显增加。(3)CuWO4/WO3复合材料的合成及PEC分解水性能研究。根据水热法可成功合成直径约为50nm的WO3纳米棒阵列,随后利用温和的浸泡-煅烧法制备CuWO4/WO3异质结。由于CuWO4沉积到WO3表面调整了该复合结构的带隙值,使得材料的光吸收明显增大。光照下,与裸露的WO3对比,CuWO4/WO3材料的光电流1.731 mA/cm2(1.23V vs RHE)增高近一倍。电化学阻抗和莫特肖特基测试表明,异质结构可显著增强载流子密度和电荷传输速率,材料能够表现较优性能。
[Abstract]:Due to the decreasing of fossil fuels and the negative effects on the environment, researchers are more and more interested in using solar energy to decompose water to produce hydrogen energy. The application of solar pyrolysis water to hydrogen production needs to reduce the cost of catalyst and improve the efficiency of decomposition water. The photochemical (PEC) decomposes the water to produce hydrogen synthetically uses the solar energy and the electric energy, this is advantageous to raise the decomposition water efficiency. In order to further improve the efficiency of water decomposition of PEC, it is necessary to improve the capture ability of incident light, the transport / separation ability of photogenerated charge and the kinetic process of water oxidation on the surface of photoanode. Semiconductor heterostructure as PEC photoanode is very effective in improving electron transmission, optical trapping ability and surface reaction efficiency. This paper focuses on the synthesis of heterooxide semiconductor materials and their applications in water decomposition by PEC. The main research contents are as follows: (1) Synthesis of 3D TiO2/ZnO heterostructures and study on the water decomposition properties of PEC. TiO2 nanorod arrays were synthesized on FTO substrates by hydrothermal method. Then TiO2 nanorod arrays were used as the substrate to modify ZnO seeds. The three-dimensional TiO2/ZnO heterostructure arrays were obtained by hydrothermal reaction in the precursor solution of ZnO. The morphology of 3D TiO2/ZnO was regulated by changing the concentration of precursor solution, reaction temperature and reaction time, and the effect on PEC activity was studied. The experimental results show that the concentration of zinc nitrate is 10mm, and the reaction temperature and time are 90oC and 3h, respectively. The photocurrent of TiO2/ZnO at 1.23 V vs RHE can reach 1.13 mA/cm2 (1.23 V vs RHE), nearly four times that of pure ZnO nanorods (0.3 mA/cm2), and nearly twice that of pure TiO2 (0.6 mA/cm2). Compared with TiO2 and ZnO photoanode, the carrier density and electron lifetime of 3D TiO2/ZnO heterostructure are improved obviously. The results of optical absorption and kinetic measurements show that the three-dimensional TiO2/ZnO heterostructure can improve the photocapture ability of the photoanode and enhance the carrier density and charge transport and separation efficiency. (2) Synthesis of WO3/ZnO heterostructure and study on PEC decomposition of water. Firstly, ZnO nanorods were grown on FTO conductive substrate by chemical bath method. The effect of reaction time on the morphology and properties of ZnO films was studied. According to the photochemical test results, the ZnO photoanode prepared at the reaction time of 3 h showed high PEC performance. WO3/ZnO heterostructure was synthesized by hydrothermal method using ammonium paratungstate as raw material and ZnO nanorod array as substrate. The photocurrent density of the photoanode, WO _ 3 / ZnO heterostructure used as the photoanode to decompose water for PEC was 1.225 mA/cm2 (1.23 V vsRHE), twice as high as that of pure ZnO photoanode (0.508 mA/cm2). It is proved by Mott-Schottky and EIS that the increase of photocurrent in WO3/ZnO heterostructure is due to the broadening of visible light response and the increase of carrier density in WO3/ZnO heterostructure. In addition, the charge separation and charge transport at the interface also increased significantly. (3) the synthesis of CuWO4/WO3 composites and the water decomposition properties of PEC. WO3 nanorods with a diameter of about 50nm were successfully synthesized by hydrothermal method, and then CuWO4/WO3 heterostructures were prepared by mild soaking and calcination. Because the CuWO4 deposited on the WO3 surface adjusts the band gap of the composite structure, the light absorption of the composite structure increases obviously. The photocurrent (1.731 mA/cm2) (1.23V vs RHE) of CuWO4 / WO _ 3 material was nearly doubled when compared with exposed WO3. Electrochemical impedance and Mott Schottky measurements show that the heterostructure can significantly enhance the carrier density and charge transfer rate, and the material can exhibit better performance.
【学位授予单位】：河南师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN303

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