質子交換膜燃料電池陰極擴散層之解析解

本論文以燃料電池的氣體擴散層部分為研究重心，藉由理論所演算出來的解析解，來探討氣體在擴散層內的一切物理特性，並了解擴散層內的局部變化量對電池I-V性能、濃度分布有何影響，試圖找出有利於氣體在擴散層內傳輸之因素，把可能造成電池內部阻抗的要素降低到最低，進而提昇電池整體性能。從本研究中得知，氣體擴散層的厚度與孔隙度是限制擴散層/觸媒層界面之氣體通量的兩個要素。當氣體擴散層厚度愈厚，則擴散時間愈長，導致單位時間單位面積觸媒層的燃氣通量減少；然而當擴散層的孔隙度下降，不僅增加氣體擴散時的阻礙，同時也會降低擴散層內的燃氣含量。研究中同時顯示，氣體在高溫下的動能高，所以氣體的擴散速率快，此時電池的I-V性能會較好，但是高溫下，燃氣的濃度卻比較低，以至於質傳損失效應會提早發生。研究結果指出，氣體在擴散層內的擴散方向主要是往觸媒層的方向，有利於反應的進行，只是這些擴散速率還是普遍偏小，約10-8 cm/s。研究中還發現，提高入口流速，流道高度變高與增加入口壓力，皆可以增加燃氣在流道與擴散層的濃度並且使氣體分布更均勻。其中，以增加燃氣入口壓力所造成的效果最好。

關鍵字

陰極擴散層；質子交換；膜燃料電池

並列摘要

The present theoretical study focuses on the performance of the gas diffusion layer (GDL) of the cathode side in proton exchange membrane fuel cells. A close form solution of a mathematical model was obtained to examine the physical properties, local current density, and concentration distribution in the GDL. Based on this analysis, it is found that the cell performance can be improved by minimizing the flow resistance in the GDL. After that, the key factors can be identified to improve the gas transport in the GDL. The current results show that the GDL thickness and porosity affect the limitation of the gas transport. The thicker the GDL, the longer it takes for the gas to diffuse across it and the greater the difference of gas concentration between its boundaries. In addition to GDL thickness, a decrease in GDL porosity increases the impedance for gas diffusion but decreases the amount of gas contained within the GDL. At high temperatures, the gas has a higher mobility and is therefore more diffusive. This improves the cell performance. However, the associated gas concentration at high temperatures is lower and the mass transport occurs slightly earlier. Also found in this study, most of the gas is diffused in the y-direction. Even so, the y-velocity component of gas is insignificant because their magnitudes are on the order of 10-8 m/s. On the other hand, the effects of gas inlet conditions and channel height on cell performance have been examined. It was found that the cell performance can be greatly enhanced by increasing the gas inlet velocity, the channel height, and the gas inlet pressure. Among these three factors, the increase in gas inlet pressure yields the highest efficiency.

並列關鍵字

PEMFC ； Cathode diffusion layer

參考文獻

[1]P. Costamagna, S. Srinivasan, “Quantum jumps in the PEMFC science and technology from the 1960s to the year 2000 PART I. Fundamental scientific aspects.” J. Power Sources 102 (2001) 242-252.

[2]P. Costamagna, S. Srinivasan, “Quantum jumps in the PEMFC science and technology from the 1960s to the year 2000 PART II. Engineering, technology development and application aspects.” J. Power Sources 102 (2001) 253-269.

[3] A.A. Kornyshev, A.A. Kulikovsky, “Characteristic length of fuel and oxygen consumption in feed channels of polymer electrolyte fuel cells.” Electrochima. Acta 46 (2001) 4389-4395.

[4] H. Dohle, A.A. Kornyshev, A.A. Kulikovsky, J. Mergel, D. Stolten, “The current voltage plot of PEM fuel cell with long feed channels.” Electrochemistry Communications 3 (2001) 73-80.

[5] A.A. Kulikovsky, “Gas dynamics in channels of a gas-feed direct methanol fuel cell：exact solutions.” Electrochemistry Communications 3 (2001) 572-579.

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質子交換膜燃料電池陰極擴散層之解析解

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