壓電式質子交換膜燃料電池研究分析

Abstract

壓電材料運用於泵之功用在於材料本身形變可使泵之腔體體積隨著壓電材料形變而變化，而此變化將造成腔體內部壓力改變，藉此可將流體吸入與排出腔體造成流量。本研究驅動壓電薄膜將空氣導入質子交換膜燃料電池之陰極端並排出不必要之水以及反應後之氣體，並將此種設計稱為壓電式質子交換膜燃料電池。當壓電材料使腔體(陰極端)體積增加時，內部壓力低於外界氣壓，空氣會被吸入於腔體內部進行電化學反應產生電流；同理、當腔體體積減小時，腔體壓力高於外界大氣壓，此刻因電化學反應生成之水將被排出電池內部以解決水管理之問題，而且其性能與陰極直接開放空氣式(Open cathode)之設計相同。換言之、因壓電材料之體積小可直接安裝於電池內部，故可省去燃料電池外接空氣泵供氣之設計，減少整體系統體積。此外本研究設計了五款壓電式質子交換膜燃料電池透過氫氣、氧氣消耗率、水生成率、壓力分佈以及電流生成等結果試圖找出其最佳化設計在不同的操作溫度、壓電材料振動頻率、肋條與反應面積比例、閥體設計。透過實驗驗證此設計，可得到最高之電流密度可達0.5A/cm2於50℃、壓電片振動頻率180Hz，換算成空氣流量可達至少每分鐘30毫升。其性能可達自然進氣以及強制進氣之性能。此外、本研究也透過理論模擬分析壓電式質子交換膜燃料電池之性能、質傳等結果與實驗相互比較驗證。

The amplitude of the vibration of a piezoelectric (PZT) device produces an oscillating flow that changes the chamber volume along with the curvature variation of the diaphragm. In this study, an actuating micro-diaphragm with a piezoelectric device is utilized in an air flow field in proton exchange membrane fuel cell (PEMFC) systems, called PZT-PEMFC. This newly designed gas pump, with a piezoelectric actuation structure, can feed air into the system of an air-breathing PEMFC. When the actuator moves outward to increase the cathode channel volume, the air is sucked into the chamber; moving inward decreases the channel’s volume and compresses air into the catalyst layer, thus enhancing the electrochemical reaction. In addition, the PZT-PEMFC solves the water-flooding problem for fuel cells, since its performance serves as an open cathode stack configuration and can be applied in a fuel cell stack without an external air supply device. The objective of the study proposes five different PZT-PEMFCs to be used for determining the optimal cell performance under different open-area ratios, PZT vibration frequencies, valve designs, and flow field designs. Besides, the reaction area is 4 cm2. The maximum power density is around 0.18 W/cm2 under normal operating temperatures, which for the PZT-PEMFC of this study is 50℃, and the optimal vibration frequency is 180Hz. Furthermore, the 3-D theoretical model for PZT-PEMFCs is also developed to investigate its characteristics and performance to make comparisons with experimental results.