| 摘要: | 第一部份，探討AM 1.5(G)太陽光於光電化學法產氫的熱力學分析。因裂解水的能量隨著反應器的溫度升高而降低，故利用太陽光長波能量加熱反應器可增加產氫的效率。 半導體光電極能隙的增加會降低光電流的輸出，當AM 1.5(G)太陽光全部激發成電子產生光電流，理論最大的光電流為63.8 mA/cm2。對半導體能隙2.0 eV及3.0 eV的理論最大光電流分別為12.4 mA/cm2及1.29 mA/cm2。太陽光理論最大功率轉換效率為44.1 %，對能隙2.0 eV及3.0 eV的功率轉換效率則分別為24.7 %及3.9 %。探討溫度及量子效率上，當溫度為647 K及量子效率為30 %時，半導體能隙為2.0 eV及3.0 eV的理論最大產氫量分別為47.5 L/m2-hr及8.0 L/m2-hr；而理論最大產氫效率則分別為16.1 %及2.7 %。增加量子效率較提升反應器溫度能更有效地增加產氫量及產氫量效率，但若固定量子效率下，提升反應器溫度對增加產氫量及產氫效率為一非常有效的方法。 第二部份，探討4種不同光電化學法產氫反應器的熱傳設計及熱流特性。AM 1.5(G)太陽光根據半導體光電極的能隙，分為短波及長波。短波能量用來產生電子與電洞對，長波能量則利用於加熱反應器。由於裂解水所需的能量隨溫度升高而降低，故利用長波能量加熱反應器可增加系統效率。因此，長波能量如何利用來加熱反應器，為非常重要的課題。 結果顯示，越多長波能量被反應器所吸收，產氫量及產氫效率越高。D設計下，太陽光強度為4000 W/m2及量子效率為30 %時，產氫量及產氫效率於能隙2.0 eV分別為186.5 L/m2-hr及15.9 %。光電化學法產氫反應器參數設計的影響，將於本論文中詳細討論。 In partⅠ, the thermodynamic analysis of photoelectrochemical (PEC) hydrogen production is performed in this thesis for air mass 1.5 solar irradiation. Because the energy required for splitting water decreases as temperature is increased, heating the system by using the long wavelength energy will increase the system efficiency. As the energy band gap of the photoelectrode increases, the induced photo-current is decreased. If photons absorbed are all excited, the maximum photo-current is 63.8 mA/cm2. For energy band of 2.0 eV and 3.0 eV, the maximum photo-current is respectively 12.4 mA/cm2 and 1.29 mA/cm2. The maximum power conversion efficiency of a PEC cell is 44.1 %. For 2.0 eV and 3.0 eV, the power conversion efficiency is 24.7 % and 3.9 %, respectively. At 647 K and quantum efficiency=30 %, the maximum hydrogen production rate is 47.5 L/m2-hr and 8.0 L/m2-hr for 2.0 eV and 3.0 eV, and the maximum solar-to-hydrogen efficiency is 16.1 % and 2.7 % for 2.0 eV and 3.0 eV, respectively. In order to increase the maximum hydrogen production rate and the solar-to-hydrogen efficiency, it is more effective to raise the quantum efficiency than raising the reaction temperature. But for fixed quantum efficiency, raising the reactor temperature is also an effective way to increase the solar-to-hydrogen efficiency. In part Ⅱ, the heat transfer and flow characteristics of a PEC hydrogen generation reactor are investigated numerically. Four different reactor designs are considered. The solar irradiation is separated into short and long wavelength parts depending on the energy band gap of the photoelectrode used. While short wavelength part is used to generate electron and hole pairs, the long wavelength part is used to heat the system. Because the energy required for splitting water decreases as temperature is increased, heating the reactor by using the long wave energy increases the system efficiency. Thus, how the long wavelength energy is absorbed by the reactor is very important. The results show that more long wavelength energy kept inside the reactor can increase the solar-to-hydrogen efficiency. For energy band gap of 2.0 eV photoelectrode, careful reactor design can increase solar-to-hydrogen efficiency by 9.7 %. For design D under 4000 W/m2 irradiation and a quantum efficiency of 30 %, is found to be 15.9 % and the hydrogen volume production rate is 186.5 L/m2-hr for 2.0 eV. Effects of several parameters on the PEC hydrogen reactor are discussed in detail. |
