| 摘要: | 在全球環境保護意識提升的情況下，尋找新興能源必然是現在全世界面臨的重要議題之一，而燃料電池為具有潛力發展的綠色能源，因為產物為水所以對環境污染較不嚴重，燃料電池依電解質的不同分為很多種類，其中質子交換膜燃料電池為近代發展較成熟之一，故本研究使用質子交換膜燃料電池作為探討方向。
提高溫度不但可以提升電池性能，還可以不必擔心因為排水困難而積水。本論文以五級高溫型質子交換膜燃料電池堆進行抗CO容忍度測試，提高溫度能有效改善電池堆CO容忍度，但溫度超過160 ⁰C後，提高溫度對CO容忍度之影響則會變小。另一方面，本研究導入滲氧法，觀察此方法對CO容忍度之影響。實驗結果發現，在高溫度及高CO濃度下，滲氧法對電池堆CO容忍度並沒有明顯幫助，可是在低溫度及低CO濃度下，滲氧法則能有較顯著的效果，此現象可歸因於CO氧化反應之放熱特性，以及燃料電池於高溫下本身所具有之高CO容忍度。本研究亦使用H2、CO、N2、CH4四種氣體所混和而成之模擬重組氣來進行CO容忍度測試，結果顯示當氫氣濃度由高降到低時，因為氫氣被稀釋，進而加強CO毒化現象，導致電池堆性能明顯下降，此時提高操作溫度有助於抑制CO於觸媒上之吸附反應，可增加電池堆CO之容忍度。而在滲氧法對重組氣之影響方面，同樣是在低溫度及低CO濃度下才會有較顯著效果，提高滲氧法之空氣濃度反而會因為稀釋氫氣導致電池堆性能下降。
Due to the future shortage of fossil fuel, discovery of new energy sources becomes one of the important global issues. The fuel cell is a green energy technology of great potential because the main product of fuel cells is water. Therefore, using fuel cells will not impact on the environment seriously. Fuel cells can be classified according to the type of electrolyte. Among all kinds of fuel cell, the proton exchange membrane fuel cell is one of the most well-developed types. Thus, the proton exchange membrane fuel cell is selected as the target in this work.
Increasing the operative temperature can not only theoretically increase the fuel cell performance, but also can solve the flooding problem in a low temperature proton exchange membrane fuel cell. In this research, a 5-cell high temperature proton exchange membrane fuel cell stack was used to study the CO tolerance of the stack.
The experimental results show that increasing the temperature increases the CO tolerance of the stack effectively. However, the influence of operative temperature becomes not significant anymore at temperature higher than 160 oC. Moreover, the air-bleeding method was introduced in this study to examine it's effect on the CO tolerance. The experimental results disclose that the effect of air-bleeding on the CO tolerance is not significant at higher temperatures and higher anodic inlet CO concentrations. Nevertheless, the effect of air-bleeding on the CO tolerance becomes remarkable. This is due to the exothermic nature of CO oxidation reaction and the intrinsic high CO tolerance of fuel cells at high temperatures. In addition, the simulated reformate gases which comprised H2, CO, N2 and CH4 were used as the fuel to understand the CO tolerance of the stack in the second part of this thesis. The data show that the stack performance drops obviously as the H2 concentration decreases. owing to a stronger CO adsorption reaction at diluted H2 conditions. On the other hand, elevating the operative temperature can as well improve the CO tolerance under low H2 concentrations. Regarding the effect of air-bleeding under H2/CO/N2/CH4 reformate gases, it is as well observed that introducing air-bleeding improve the CO tolerance only at low operative temperatures and low CO concentrations. Different from the results of tests under H2/CO mixtures, an excess air concentration may lead to a performance drop. |
