質子交換膜燃料電池用新型膜電極組材料之開發與其性質研究

Development of the Novel Materials of Membrane Electrode Assembly for Proton Exchange Membrane Fuel Cell

洪太峰(TaiFeng Hung)

指導教授 ： 陳玉惠

中原大學/理學院/化學研究所/博士(2009年)

https://doi.org/10.6840/cycu200900863

摘要

質子交換膜燃料電池之電化學反應主要發生在膜電極組，因此膜電極組被視為其核心元件之一。本研究以簡單且價格低廉的方法開發新型膜電極材料，其內容主要分為三部分：

第一部分：新型單層氣體擴散層之開發與性質研究
本部份研究以物理混摻及低溫壓延的製程成功地製備一含氣相成長奈米碳纖維之高效能單層氣體擴散層。掃描式電子顯微鏡結果顯示：此含氣相成長奈米碳纖維之單層氣體擴散層具有類似微孔層之結構。同時，線狀的氣相成長奈米碳纖維均勻分散且與碳黑交錯於單層氣體擴散層基材中。由於氣相成長奈米碳纖維的存在，單層氣體擴散層之相關性質如電子阻抗、機械性質、氣體滲透率與疏水性隨氣相成長奈米碳纖維含量而改變。在膜電極組製備過程中，此單層氣體擴散層可直接用以塗佈觸媒層。在氫氣/氧氣或氫氣/空氣的測試系統中，添加15 wt. % 氣相成長奈米碳纖維之單層氣體擴散層所組成之單電池最佳效能比未添加氣相成長奈米碳纖維所得到之結果高出63 %，且其效能在陽、陰極加濕溫度分別為80 ℃與65 ℃及電池溫度為65 ℃操作條件下約為市售E-Tek ELAT雙層氣體擴散層之85 %。

第二部分： Nafion®自增濕複合膜之製備與性質研究
此部份之研究乃採用溶液鑄膜法成功地製備一含磺酸化白金/奈米碳纖維之Nafion®自增濕複合膜。由掃描式電子顯微鏡與能量散佈分析儀結果指出：由於Nafion®與磺酸化白金/奈米碳纖維之間良好的相容性，使得磺酸化白金/奈米碳纖維均勻分散於複合膜之中。相較於含未磺酸化白金/奈米碳纖維之Nafion®自增濕複合膜，含磺酸化白金/奈米碳纖維之Nafion®自增濕複合膜之相關性質如電子阻抗、離子交換當量、含水率、尺寸安定性及催化活性均明顯提升。於乾燥的氫氣/氧氣及電池溫度為50 ℃之操作條件下，含磺酸化白金/奈米碳纖維之Nafion®自增濕複合膜所組裝之質子交換膜燃料電池其最大功率密度約為921 mW cm-2，比含白金/奈米碳纖維之Nafion®自增濕複合膜之結果高出34 %。

第三部分：新型自增濕膜電極組之研究
此部份以第一及第二部分之研究結果為基礎，組裝一新型自增濕膜電極組並探討氣體擴散層在乾燥的氫氣/氧氣與不同電池溫度之測試條件下對含磺酸化白金/奈米碳纖維之Nafion®自增濕複合膜單電池效能影響。結果顯示：在電池溫度高於70 ℃時，由單層氣體擴散層所組成之單電池 (FC-G2) 效能優於由碳布所組成之單電池 (FC-G1)。在電池溫度為80℃時，FC-G2最大功率密度比FC-G1高出38倍。此明顯的改善可歸因於由含磺酸化白金/奈米碳纖維之Nafion®自增濕複合膜所產生的水有效地被保存在自增濕膜電極組中。

關鍵字

自增濕複合薄膜 ； 白金觸媒 ； 碳奈米纖維 ； 質子交換膜燃料電池 ； 膜電極組 ； 氣體擴散層

並列摘要

The electrochemical reactions of proton exchange membrane fuel cell (PEMFC) mainly occur in the membrane electrode assembly (MEA), thus, MEA is regarded as an important part of the core components for PEMFC. The novel materials for gas diffusion layer (GDL) and proton exchange membrane (PEM) of MEA are developed in this study and the content is divided into three parts as following:

Part 1: Development and properties of the novel single-layer gas diffusion layer (SL-GDL)
In this part, a high efficiency SL-GDL is successfully prepared by addition of a vapor grown carbon nanofiber (VGCF) in the carbon black/poly(tetrafluoroethylene) composite-based SL-GDL through the physical blending and low-temperature calendering process. The scanning electron micrographs of the as-prepared SL-GDLs show that the GDL samples had a microporous layer (MPL)-like structure, while the wire-like VGCFs are well dispersed and crossed among the carbon black particles in the SL-GDL matrix. Due to the presence of VGCFs, the related properties of the SL-GDL, including electronic resistivity, mechanical characteristic, gas permeability, and water repellency, vary with the VGCF content and an optimal composition, which is beneficial to the performance of the PEMFC, is obtained. The MEA fabricated with the as-prepared SL-GDL is carried out by direct coating with a catalyst layer. The best performances obtained from the PEMFC with VGCFs at 15 wt. % are approximately 63 % higher than those without VGCFs, and are about 85 % as efficient as ELAT GDL, a commercial dual-layer GDL, for both the H2/O2 and H2/air systems.
Part 2: Preparation and characterization of the Nafion®-based self-humidifying composite membrane (N-SHCM)
In this part, the sulfonated carbon nanofiber-supported Pt catalyst (s-Pt/CNF)-containing N-SHCM, N-s-Pt/CNF, is successfully prepared by using the solution-casting method. The scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) images of N-s-Pt/CNF indicate that s-Pt/CNF is well dispersed in the Nafion® matrix due to the good compatibility between Nafion® and s-Pt/CNF. Comparing with that of the non-sulfonated Pt/CNF-containing N-SHCM, N-Pt/CNF, the related properties of N-s-Pt/CNF, including electronic resistivity, ion-exchange capacity, water uptake, dimensional stability as well as catalytic activity are significantly increased. The maximum power density of the PEMFC fabricated with N-s-Pt/CNF operated at 50 ℃ under the dry H2/O2 condition is approximately 921 mW cm-2, which is about 34 % higher than that with N-Pt/CNF.
Part 3: Study of the self-humidifying membrane electrode assembly (SH-MEA)
In this part, a novel self-humidifying membrane electrode assembly (SH-MEA) composed of the catalyst-coated SL-GDL and N-s-Pt/CNF was fabricated to investigate the effect of GDL on performance of the PEMFC under the dry H2/O2 condition at various cell temperatures. It is found that the PEMFC fabricated with SL-GDL (FC-G2) exhibits better performance than that with carbon cloth-GDL (FC-G1) at the cell temperature higher than 70 ℃. The maximum power density obtained at 80 ℃ from FC-G2 is approximately 38-fold higher than that from FC-G1. The significant improvement in the performance is ascribed to the more effective retention of the water generated from N-s-Pt/CNF due to the morphology of SL-GDL.

並列關鍵字

Platinum catalyst ； Gas diffusion layer ； Self-humidifying composite membrane ； Carbon nanofiber ； Membrane electrode assembly ； Proton exchange membrane fuel cell

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