爲了實現清潔的和可持續的能源供應，直接利用太陽能產生化學能的研究已持續多年。特別地，因為只需要廣泛分佈于地球表面的水和太陽光做原材料，半導體光電極光電解水產生氫氣引起了極大的關注。因為易於獲取和高的太陽能到氫能理論轉化效率，地球富有及對可見光響應的材料對于這種應用是值得期待的。在這篇論文中，我們製備并表徵了基於硫化鎘和銅氧化物的光電極以研究它們的光電水解能力。 / 作為一種帶隙相對窄的半導體，硫化鎘(2.4eV)擁有比水還原電位更負的導帶邊和比水氧化電位更正的價帶邊，這使得n 型和p 型硫化鎘可以分別成為良好的光電陽極和光電陰極材料。大約2μm 厚的硫化鎘薄膜沉積在與其形成歐姆接觸的鉬背電極上。因為易於形成硫空位，這樣製備的硫化鎘是本征n 型導電，它通過可控的銅原子熱擴散以取代鎘形成受主態可以被轉化為p 型。研究發現對於水的光電分解最合適的銅摻雜濃度是5.4%。 / 作為一種金屬氧化物，氧化亞銅(2.0eV)是另一種引起高度關注的光電極材料。通過熱氧化電沉積在金襯底上的銅膜和銅納米線，薄膜和高度有序納米線陣列的氧化亞銅都被成功製備。因為形成銅空位，氧化亞銅呈現p 型導電。在相同的光照條件下，氧化亞銅納米線光電極的光電流是薄膜的兩倍。同時，氧化亞銅光電極遭受嚴重的光致還原分解。氧化銅和二氧化鈦保護層對其表面的修飾避免了氧化亞銅和電解液的直接接觸。相對於裸露的氧化亞銅納米線陣列，Cu₂O/CuO/TiO₂同軸納米纜光電極獲得了74%光電流和4.5 倍穩定性的提升。 / 此外，共催化劑也被用來修飾光電極表面以減小水分解的過電勢，它們可以促進光生載流子從光電極到電解液的轉移。實驗發現屬於鈷基共催化劑的Co²⁺和Co₃O₄ 提高了本征n 型硫化鎘光電陽極的穩定性。鉑有效地消除了銅摻雜硫化鎘光電陰極的暫電流，同時提高了光電流和穩定性及正向移動陰極光電流起始電勢達90 mV。此外，氫氣從CdS:Cu/Pt 光電陰極的析出也被首次探測到。 / 這篇論文不僅研究了硫化鎘和氧化亞銅的水光電解能力，同時也提出可廣泛應用于防止光腐蝕和提高光活性的普適方法。它們可以應用于其它的可見光響應及地球富有的材料以擴大光水解的材料選擇空間。 / With the aim of creating a clean and sustainable energy supply, the direct use of solar energy to produce chemical energy has been pursued for many years. Particularly, the photoelectrolysis of water to generate hydrogen by semiconductor photoelectrodes has attracted great attention because of its advantage of using only water and sunlight, both of which are widely distributed, as raw materials. The earth abundant and visible light absorbing materials are promising for this application for the advantages of easy access and high theoretical solar to hydrogen conversion efficiency. In this thesis, the cadmium sulfide based and copper oxide based photoelectrodes were fabricated and characterized to determine their potential for photoelectrolysis. / As one of the semiconductors with relatively narrow band gap, CdS (2.4eV) has a conduction band edge more negative than the water reduction potential level and a valence band edge more positive than the water oxidation potential level, enabling n-type CdS and p-type CdS as good candidates for photoanode and photocathode respectively. CdS thin film with thickness around 2μm was deposited onto Mo back contact on glass, which formed ohmic contact with CdS. The as-prepared CdS was intrinsic n-type due to the easy formation of sulfur vacancies and it was converted to p-type by the controlled thermal diffusion of copper atoms which substituted cadmium to produce acceptor state. The optimal Cu doping level for the interest of water photoelectrolysis was found to be at 5.4% concentration. / Cu₂O with band gap of 2.0eV is another attracting competitor for the photoelectrode among the metal-oxide semiconductors. Both thin film and highly aligned nanowire arrays Cu₂O were prepared by thermal oxidation of Cu film and Cu nanowires on Au substrates synthesized by electrodeposition. Cu₂O was found to be p-type because of the copper vacancies. The photocurrent of the Cu₂O nanowires photocathode was found to be twice that of the Cu₂O film, and the bare Cu₂O photocathode suffered from a significant photo-induced reductive decomposition. By modifying the surface of the Cu₂O nanowires with protecting layers of CuO and TiO₂, direct contact of Cu₂O with the electrolyte was avoided, and the Cu₂O/CuO/TiO₂ coaxial nanocable structures were found to gain 74% higher photocurrent and 4.5 times higher stability. / Furthermore, the co-catalysts were also used to modify the photoelectrode surface to reduce the water splitting overpotentials by facilitating the transfer of the photo-induced carriers to the electrolyte. Cobalt based co-catalysts, both the Co²⁺ and Co₃O₄ thin film, enhanced the stability of the intrinsic n-CdS photoanode. The Pt modification of CdS:Cu, effectively eliminating the large transient photocurrent, enhanced the photocurrent and stability and positively shifted the onset potential of the cathodic photocurrent by 90 mV, and the hydrogen evolution from the p-type CdS:Cu/Pt photocathode was observed for the first time. / This thesis not only studied the water photoelectrolysis potentials of CdS and Cu₂O, but also presented general methods to prevent photocorrosion and enhance photo-activity, which could be also applied to other visible light responsive and earth abundant materials to enlarge the range of material choice for solar water splitting. / 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. / Huang, Qiang = 由地球富集元素構成可見光驅動的水光電解電極 / 黃强. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Huang, Qiang = You di qiu fu ji yuan su gou cheng ke jian guang qu dong de shui guang dian jie dian ji / Huang Qiang. / Chapter Chapter 1. --- General Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Solar water splitting --- p.4 / Chapter 1.2.1 --- Material challenges --- p.6 / Chapter 1.2.2 --- Photocatalyst and photoelectrolysis cells --- p.8 / Chapter 1.3 --- Visible light responsive materials for water photoelectrolysis --- p.9 / Chapter 1.3.1 --- Metal oxides --- p.10 / Chapter 1.3.2 --- Non-metal oxides --- p.12 / Chapter 1.4 --- Research objectives --- p.14 / Chapter 1.5 --- References --- p.15 / Chapter Chapter 2. --- Preparation and Photoelectrochemical Properties of CdS:Cu with p-type Conductivity --- p.21 / Chapter 2.1 --- Introduction --- p.21 / Chapter 2.2 --- Experimental --- p.23 / Chapter 2.2.1 --- Photoelectrode preparation --- p.23 / Chapter 2.2.2 --- Photoelectrode characterization --- p.23 / Chapter 2.3 --- Results and discussion --- p.25 / Chapter 2.3.1 --- Comparative study of intrinsic n-CdS and Cu doped CdS --- p.25 / Chapter 2.3.2 --- Importance of Ohmic back contact --- p.29 / Chapter 2.3.3 --- Optimal Cu doping concentration --- p.32 / Chapter 2.4 --- Conclusions --- p.35 / Chapter 2.5 --- References --- p.36 / Chapter Chapter 3. --- Preparation and Photoelectrochemical Properties of Cu₂O Nanowire Arrays based Photocathodes --- p.39 / Chapter 3.1 --- Introduction --- p.39 / Chapter 3.2 --- Experimental --- p.40 / Chapter 3.2.1 --- Photocathode preparation --- p.40 / Chapter 3.2.2 --- Photocathode characterization --- p.42 / Chapter 3.3 --- Results and discussion --- p.43 / Chapter 3.3.1 --- Structural characterization --- p.43 / Chapter 3.3.2 --- Photoelectrochemical investigations --- p.48 / Chapter 3.3.3 --- The factors affecting the photocathodes’ stability --- p.51 / Chapter 3.3.4 --- The advantages of Cu₂O/CuO/TiO₂ configuration --- p.54 / Chapter 3.4 --- Conclusions --- p.62 / Chapter 3.5 --- References --- p.63 / Chapter Chapter 4. --- Modifying Photoelectrode Surface with Water Splitting Co-catalysts --- p.66 / Chapter 4.1 --- Introduction --- p.66 / Chapter 4.2 --- Experimental --- p.67 / Chapter 4.2.1 --- Co-catalyst deposition --- p.67 / Chapter 4.2.2 --- Characterization --- p.68 / Chapter 4.3 --- Results and discussion --- p.69 / Chapter 4.3.1 --- n-CdS photoanode modified with Co based co-catalyst --- p.69 / Chapter 4.3.2 --- Cu₂O/CuO/TiO₂ photocathode modified with Pt nanoparticles --- p.73 / Chapter 4.3.3 --- CdS:Cu photocathode modified with Pt nanoparticles --- p.77 / Chapter 4.3.3.1 --- Pt nanoparticles deposited by electrodeposition --- p.77 / Chapter 4.3.3.2 --- Pt nanoparticles deposited by DC sputtering --- p.77 / Chapter 4.3.3.3 --- Hydrogen evolution --- p.80 / Chapter 4.4 --- Conclusions --- p.82 / Chapter 4.5 --- References --- p.83 / Chapter Chapter 5. --- Conclusions --- p.86
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_328149 |
| Date | January 2013 |
| Contributors | Huang, Qiang, Chinese University of Hong Kong Graduate School. Division of Physics. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | electronic resource, electronic resource, remote, 1 online resource (xv, 88 leaves) : ill. (some col.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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