P-type Semiconductor Materials for Photoelectrochemical and Photocatalytic Water Splitting

本学位论文主要探讨了两种p型半导体材料的制备、表征和应用：氧化亚铜（Cu2O）以及锡磷硫三元化合物（Sn2P2S6）。第一部分针对高效氧化亚铜光阴极的开发。首先以铜为基底用一种新的湿化学方法制备出了高活性的氧化亚铜光阴极。进一步我们将氧化亚铜修饰在铜纳米线阵列上合成了一种新的光阴极。第二部分对Sn2P2S6作为一种新型可见光响应的光催化剂进行了探讨。第一章：基于单质铜和二价铜离子之间存在的氧化还原反应，用一种新颖的湿化学方法在铜基底上制备出了具有极高光电催化性能的氧化亚铜膜。在标准强度模拟太阳光照射下，该光阴极在可逆氢电极电位产生的光电流达到了创纪录的4.8 mA cm-2。通过电镜表征发现，原位生长的氧化亚铜晶体和铜基底有着牢固的结合。在修饰了铝掺杂的氧化锌和二氧化钛保护层之后，该氧化亚铜光阴极用于光电催化分解水的效率和稳定性得到进一步提升。第二章：将氧化亚铜修饰到铜纳米线阵列上，得到一种更高效的光阴极。由于氧化亚铜本身的载流子扩散距离短而吸光所需路径长，而纳米线的构型有利于克服这两者不匹配的问题。同时，每根纳米线内部的铜具有良好的导电性，提供了氧化亚铜和外电路之间进行电荷传输的路径。光电测试结果显示，该光阴极产生的光电流大于平面构型的氧化亚铜和传统带有很多裂口的氧化亚铜纳米线。第三章：通过一步球磨加一步煅烧的方法合成了Sn2P2S6。利用X射线衍射、X射线光电子能谱、扫描电镜以及透射电镜对合成得到的Sn2P2S6进行了表征。结合紫外可见漫反射光谱、莫特肖特基曲线和光电子能谱价带谱的结果分析得到了Sn2P2S6的能带位置。伴随2.1 eV的带隙，Sn2P2S6在可见光下显示出了良好的光催化产氢性能。进一步通过光电催化测试表明，Sn2P2S6作为一种p型半导体可以应用于光阴极材料。附录一：以红磷和硫酸镍为原料，通过一步水热法制备了负载磷化镍（Ni2P）的红磷。该复合物的光催化产氢性能为纯红磷的13倍，以及负载铂的红磷的2倍。在该复合物中，磷化镍起到了助催化剂的作用，并且促进了红磷中光生电子空穴对的分离。附录二：本工作设计开发了一个用于制备固态太阳能电池的教学实验。通过化学浴沉积法在n型硅片表面修饰了一层硫化铜薄膜，随之形成的p-n结有明显的光伏效应。该项目使得学生有机会可以亲自动手制备固态太阳能电池。This thesis focuses on the preparation, characterization and applications of two kinds of p-type semiconductor materials: cuprous oxide (Cu2O) and tin hypothiodiphosphate (Sn2P2S6). In the first part, a highly active Cu2O photocathode was obtained using a facile wet-chemistry method. Furthermore, highly aligned Cu nanowire arrays coated with Cu2O as photocathodes were designed and fabricated. In the second part, Sn2P2S6 as a new visible-light-driven photocatalyst for hydrogen production from water was explored.In the first chapter, a highly photoactive Cu2O film was formed on Cu substrate via a novel wet-chemistry method based on a simple redox reaction between Cu and Cu2+. The Cu mesh/Cu2O photocathode exhibited excellent photoelectrochemical performance with a record high photocurrent of 4.8 mA cm-2 at 0 V vs. RHE under AM 1.5G simulated sunlight. Characterization by SEM and TEM revealed that the in-situ grown Cu2O crystals adhered firmly to the Cu substrate. After coating protective layers of Al:ZnO and TiO2, this Cu2O-based photocathode showed higher efficiency and stability toward PEC water splitting.Then Cu2O crystals were coated on highly aligned Cu nanowire arrays to construct a more efficient photocathode. The nanowire configuration is known to overcome the mismatch between the short carrier diffusion length and the long light absorption path of Cu2O. In addition, the conducting Cu inside the nanowires provides direct pathway for efficient charge transfer between Cu2O and substrate. As a result, this photocathode generated a larger photocurrent than that of planar configuration and conventional Cu2O nanowires with many isolated fractures.In the third chapter, a new visible-light-driven photocatalyst Sn2P2S6 was prepared through a mechanical ball milling process followed by a calcination step. The obtained Sn2P2S6 nanoparticles were characterized by X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The energy band position of Sn2P2S6 was determined by the combination of UV-Vis diffuse reflectance spectroscopy (DRS), Mott–Schottky plot and XPS valence band spectrum. With a bandgap of 2.1 eV, the as-prepared Sn2P2S6 exhibited good photocatalytic hydrogen production activities under visible light irradiation. Moreover, the PEC analysis showed the potential of p-type Sn2P2S6 as a photocathode material.Appendix I: Ni2P-loaded red phosphorus (Ni2P-P) was prepared from red phosphorus (red P) and nickel sulfate by a hydrothermal method. The photocatalytic H2 production activity of Ni2P-P was about 13 times higher than that of pure red P and 2 times higher than that of Pt-loaded red P. In the composite, Ni2P is believed to serve as an efficient cocatalyst to facilitate the separation of photogenerated electron-hole pairs from red P.Appendix II: A laboratory experiment for the fabrication of a solid-state photovoltaic cell was developed. A copper sulfide film was coated onto an n-type silicon wafer via a chemical bath deposition method. The resulting p-n junction shows obvious phJin, Zexun.Thesis Ph.D. Chinese University of Hong Kong 2016.Includes bibliographical references (leaves ).Abstracts also in Chinese.Title from PDF title page (viewed on …).Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only