壓電可變式流道質子交換膜燃料電池之效率分析

Abstract

由本實驗室過去研究得知改變壓電元件振幅可使薄膜曲率發生變化進而造成腔體體積之變動。本研究在質子交換膜燃料電池系統之流道上以相似之制動方式將壓電薄膜應用在質子交換膜燃料電池上，命名為壓電可變式質子交換膜燃料電池。此新設計系利用壓電制動方式之氣體泵可供給自然進氣質子交換膜燃料電池所需之空氣，壓電薄膜向上拉伸增加腔體體積時，空氣會因為壓力差而被吸入腔體中，當壓電薄膜壓回初始位置，減少腔體之體積，此時腔體內之部分空氣被壓入觸媒層中增強電池之化學反應。壓電可變式燃料電池空氣標準循環可成功的描述自然進氣壓電可變式燃料電池之運作方式，本研究已建立一三維、暫態之壓電可變式質子交換膜燃料電池模組，並探討電池中之各種現象與電池之整體效率。進一步來說，在高頻率時，壓電薄膜之制動方式可產生更穩定電流輸出、排出多餘水氣、吸進更多空氣量與更高氫氣消耗量，且可有效克服濃度極化，此外當量比在壓電可變式燃料電池中為一重要參數，在貧燃料之情況下，自然進氣之壓電可變式燃料電池可節省更多氫氣與逐步增加電流值之生成。

Previous studies showed that the amplitude of vibration of a piezoelectric (PZT) device produces an oscillating flow which changes the chamber volume along with curvature variation of the diaphragm. In a similar way, the actuating micro-diaphragm with piezoelectric effects is utilized as one of the flow channels PEM fuel cell systems, named as PZT-PEMFC. This newly designed gas pump with a piezoelectric actuation structure can feed air into the system of an air-breathing PEM fuel cell. While the actuator is moving outward to increase the cathode channel volume, the air is sucked in the chamber; moving inward to decrease the cathode channel volume, then air is compressed into the catalyst layer and enhances the chemical reaction. Also, the air-standard PZT-PEMFC Cycle is proposed to describe an air-breathing PZT-PEMFC. At the same time, a novel design of PZT-PEMFC’s has been developed and a three-dimensional, transitional model has been successfully built to account for its major phenomena and the fuel cell performance. Moreover, at high frequencies, PZT actuation leads to more stable current output, drained water, sucked oxygen, higher hydrogen consumption, and also overcomes the concentration losses. In addition, the equivalent ratio is used as an important parameter for the novel PZT-PEMFC. At hydrogen lean condition, an air-breathing PZT-PEMFC saves more hydrogen and gradually increases the current generation.