質子交換膜燃料電池用碳奈米管/高分子奈米複合材料雙極板之製備與性質研究

Preparation and Properties of Carbon Nanotubes/Polymer Nanocomposite Bipolar Plates for Proton Exchange Membrane Fuel Cells

廖述杭(Shu-Hang Liao)

指導教授 ： 馬振基

國立清華大學/工學院/化學工程學系/博士(2010年)

摘要

本研究旨在探討多壁碳奈米管(MWCNTs)及官能基化多壁碳奈米管(Functionalized MWCNTs)於質子交換膜燃料電池(PEMFCs)複合材料雙極板之製備及性質，並研究其組裝成燃料電池之性能。
本研究主要可分為四個部分：
第一部分探討一新型具交聯點之多壁碳奈米管（MWCNTs）用於強化乙烯酯樹脂複合材料雙極板之相關性質。先將poly(oxyalkylene)-amines (POA) 接枝 maleic anhydride (MA)－POAMA，再透過醯胺化反應將之接枝於多壁碳奈米管(MWCNTs-POAMA)。於MWCNTs-POAMA/乙烯酯樹脂奈米複合材料中，MWCNTs-POAMA可與乙烯酯樹脂反應形成部分交聯結構，而不是一個分相的組成物。研究結果發現MWCNTs-POAMA比pristine MWCNTs具有較佳的分散性。除此之外，乙烯酯樹脂複合材料雙極板之機械性質和導電性質具有顯著的改善。MWCNTs-POAMA/乙烯酯樹脂奈米複合材料雙極板的抗折強度從28.54 MPa增加至41.44 MPa;而體積導電度則從156 S cm-1增加至 643 S cm-1，分別提升45 %和315 %。另一方面，以所有配方之製成之複合材料雙極板都無氣體洩漏的現象。將MWCNTs-POAMA/乙烯酯樹脂奈米複合材料雙極板組裝成燃料電池單電池進行測試，最大電流從1.03 A cm-2增加至1.23 A cm-2； 最大電功率密度從0.366 W cm-2增加至0.518 W cm-2，顯示MWCNTs-POAMA/乙烯酯樹脂奈米複合材料具有較高的電子轉移能力，可有效使用於質子交換膜燃料電池。

第二部分探討以自由基改質法一步於碳奈米管上接枝分子量400及2000的POAMA，簡稱MWCNTs/MA-POA400和MWCNTs/MA-POA2000。經由有機溶劑之溶解測試及SEM型態學分析，顯示MWCNTs/MA-POA2000比pristine MWCNTs有更好的溶解性，並於乙烯酯樹脂基材中有較佳的分散性。再進一步研究改質碳奈米管/乙烯酯樹脂奈米複合材料雙極板之抗折強度、體積導電度、氣體洩露性質及燃料電池性能測試。本研究結果顯示最適化之奈米複合材料雙極板為添加MWCNTs/MA-POA2000所製備的奈米複合材料雙極板，其抗折強度由28.00 MPa (未含MWCNTs)提升至48.33 MPa (含2 wt% MWCNTs/MA-POA2000)；體積導電度由155 S cm-1 (未含MWCNTs)增加至1370 S cm-1 (含2 wt% 之MWCNTs/MA-POA2000)。另一方面，以所有配方製成之複合材料雙極板都無漏氣情形。添加1 wt% MWCNTs/MA-POA2000製備的奈米複合材料雙極板組成單電池，其最大電流密度由1.03 A cm-2 (未含MWCNTs)提升至1.32 A cm-2，電功率密度由0.392 W cm-2 (未含MWCNTs)提升至0.587 W cm-2 (含2 wt% 之MWCNTs/MA-POA2000)。因此，本研究所製備的含MWCNTs/MA-POA2000之奈米複合材料雙極板可應用於質子交換膜燃料電池。

本研究第三部分旨在探討使用碳奈米管、聚丙烯樹脂(PP)及石墨，製備燃料電池用複合材料雙極板。選用三種不同結晶度之PP－ HC-PP、MC-PP及LC-PP，所具有的結晶度分別為45.1 %、38.1 %及34.9 %，本部分研究所製備之複合材料雙極板，最適化之石墨含量為80 wt%，體積導電度由32 S cm-1提升到142 S cm-1，抗折強度由20.25 MPa提升到23.66 MPa。透過SEM鑑定碳奈米管/聚丙烯樹脂奈米複合材料之表面型態可知，LC-PP系列之複合材料能夠有效增進碳奈米管與聚丙烯樹脂彼此之間的相容性，而使碳奈米管具有最佳的分散效果。本部分研究結果獲得最佳配方為MWCNTs/LC-PP奈米複合材料雙極板，體積導電度由160 S cm-1(未含MWCNTs)提升至548 S cm-1 (含4 wt%之MWCNTs/LC-PP)；抗折強度由21.44 MPa(未含MWCNTs)提升至25.46 MPa (含8 wt%之MWCNTs/LC-PP)，所有配方之複合材料雙極板都無漏氣的現象發生。以含4 wt% MWCNTs/LC-PP製備之奈米複合材料雙極板進行燃料電池單電池的性能測試，其最大電流密度為1.19 A cm-2，電功率密度則為0.533 W cm-2。
本研究第四部分係利用聚丙烯-馬來酸酐相容劑(PP-g-MA)與胺化碳奈米管(aminated MWCNTs)經由開環反應接枝於MWCNTs上(MWCNTs/PP-g-MA)。研究結果顯示將MWCNTs/PP-g-MA導入PP奈米複合材料雙極板中，確實具有較佳的相容性而增進MWCNTs-PP之間的附著力。透過接枝長鏈段的PP-g-MA在MWCNTs上，可改善MWCNTs於PP基材中之分散性。除此之外，MWCNTs/PP-g-MA PP奈米複合材料雙極板之機械性質和導電性質具有顯著的改善。含1、2和4 wt% MWCNTs/PP-g-MA之奈米複合材料雙極板的抗折強度和體積導電度分別增加56.3、68.5及70.9 %；282、425及473 %。進一步比較最大功率密度，MWCNTs/PP-g-MA PP奈米複合材料雙極板之最大電功率密度達到0.586 W cm-1，其性能已與石墨板(0.614 W cm-1)相近，因此，本研究所製備之MWCNTs/PP-g-MA PP奈米複合材料雙極板適用於質子交換膜燃料電池。

關鍵字

燃料電池 ； 奈米複合材料雙極板 ； 碳奈米管 ； 化學改質

並列摘要

The objectives of this research are the preparation and characterization of multiwalled carbon nanotubes (MWCNTs) and functionalized MWCNTs/polymer nanocomposite bipolar plates for use in proton exchange membrane fuel cells (PEMFCs).
There are four parts in this dissertation.
The first part of this dissertation investigates the novel functionalized multi-walled carbon nanotubes (MWCNTs) which are used as cross-links between MWCNTs-vinyl ester interfaces to achieve homogeneous dispersion and strong interfacial bonding for developing fully integrated MWCNTs-vinyl ester nanocomposite bipolar plates. POAMA (i.e. poly(oxyalkylene)-amines (POA) bearing maleic anhydride (MA)) are grafted onto the MWCNTs by amidization reaction, forming MWCNTs-POAMA. In the MWCNTs-POAMA/vinyl ester nanocomposites, MWCNT-POAMAs react with vinyl ester and become part of the cross-linked structure, rather than just a separate component. It was found that MWCNTs-POAMA exhibited better dispersion in the vinyl ester matrix than those of pristine MWCNTs. Moreover, results demonstrate that the mechanical and electrical properties of the vinyl ester nanocomposite bipolar plate are improved dramatically. The ultimate flexural strength and bulk electrical conductivity of the MWCNTs-POAMA/vinyl ester nanocomposite bipolar plate are increased from 28.54 MPa to 41.44 MPa and 156 S cm-1 to 643 S cm-1, exhibiting 45 and 315 % improvement, respectively. The gas tightness of all of composite bipolar plates in this study was no leak. In addition, the maximum current and power densities of the single fuel cell test using the MWCNTs-POAMA/vinyl ester nanocomposite bipolar plates were enhanced from 1.03 to 1.23 A cm-2 and from 0.366 to 0.518 W cm-2, respectively, which suggested that a higher electron transfer ability for PEMFC applications can be achieved.

The second part of this dissertation investigates a novel one-step preparation of functionalized multi-walled carbon nanotubes (MWCNTs) by free-radical modification. MA-POA, i.e. Maleic anhydride (MA) grafting molecular weight 400 and 2,000 poly (oxyalkylene)-amines (POA400 and POA2000), was attached onto the MWCNTs, forming MWCNTs/MA-POA400 and MWCNTs/MA-POA2000. The functionalized MWCNTs, especially MWCNTs/MA-POA2000, exhibited higher solubility than the pristine MWCNTs in organic solvents and showed well dispersion in the vinyl ester matrix. Furthermore, this study also investigated the mechanical, electrical and single fuel cell properties of functionalized MWCNT nanocomposite bipolar plates for use in polymer electrolyte membrane fuel cells. The flexural strength of the nanocomposite bipolar plates containing 2 wt% MWCNTs/MA-POA2000 was increased from 28 MPa to 48.33 MPa, exhibiting 73% improvement. In addition, the bulk electrical conductivity of the nanocomposite bipolar plates was 780 % (from 156 to 1340 S cm-1) higher than those of the original composite bipolar plates by adding only a small quantity (1 wt%) of MWCNTs/MA-POA2000. The maximum current density and power density of the single cell tests of the nanocomposite bipolar plate with 1 wt% MWCNTs/MA-POA2000 were enhanced from 1.03 to 1.32 A cm-2 and from 0.392 to 0.587 W cm-2, respectively. The overall performance confirms the MWCNTs/MA-POA2000 nanocomposite bipolar plates prepared in this study are suitable for PEMFC application.

The third part of this dissertation studies the fabrication of lightweight and high performance nanocomposite bipolar plates for the application in proton exchange membrane fuel cells (PEMFCs). Three types of polypropylene (PP) with different crystallinities including high crystallinity PP (HC-PP)、medium crystallinity PP (MC-PP) and low crystallinity PP (LC-PP) were prepared. The optimum composition of original composite bipolar plates was determined with 80 wt% graphite content and 20 wt% PP content based on the measurements of electrical and mechanical properties with various graphite contents. Results indicated that MWCNTs was dispersed better in LC-PP than other PP owing to enough dispersed regions in nanocomposite bipolar plates. The good MWCNT dispersion of LC-PP causes better bulk electrical conductivity and mechanical properties of MWCNTs/PP nanocomposite bipolar plates. In the MWCNTs/LC-PP system, the bulk electrical conductivity of 4 wt% MWCNTs/LC-PP nanocomposite bipolar plates increases from 160 S cm-1 (0 wt%) to 548 S cm-1, exhibiting 242 % improvement. The flexural strength of the MWCNTs/LC-PP nanocomposite bipolar plate with 8 wt% of MWCNTs was 29.46 MPa, approximately 37 % higher than that of the original nanocomposite bipolar plate. The single cell performance of MWCNTs/LC-PP nanocomposite bipolar plate was also evaluated. The maximum current density and power density of the single cell tests of the nanocomposite bipolar plate with 4 wt% MWCNTs/LC-PP were 1.19 Acm-2 and 0.533 Wcm-2, respectively.

The four part of this dissertation investigates the preparation of aminated mullti-walled carbon nanotubes (MWCNTs-NH2) attached with polypropylene grafted maleic anhydride (PP-g-MA compatibilizer) by ring-opening reaction. The prepared MWCNTs/PP-g-MA was introduced to the PP/composite bipolar plates, to achieve a high compatibility and good adhesion between carbon nanotubes and PP matrix via PP-g-MA chains. Replacement of amine-terminated groups by PP-g-MA in the MWCNTs leads to the grafting of long copolymer chains to the MWCNTs, and improves the dispersion of MWCNTs. Due to the strong reinforcing properties of MWCNTs, the electrical and mechanical properties of the PP composite bipolar plates were enhanced. The effect of incorporating MWCNTs/PP-g-MA on the morphology, electrical and mechanical properties of the PP-based composite bipolar plates was studied. The resulting PP composite bipolar plates with 1, 2, and 4 wt% of MWCNTs/PP-g-MA demonstrate the flexural strength and the bulk electrical conductivity were improved by 56.3, 68.5, and 70.9 % and by 282, 425, and 473 %, respectively. Comparing with the maximum power density of the graphite bipolar plates (0.614 W cm-2), the MWCNTs/PP-g-MA PP nanocomposite bipolar plates (0.586 W cm-2) are suitable for bipolar plates of PEMFCs.

並列關鍵字

fuel cell ； nanocomposite bipolar plate ； carbon nanotube ； chemical modification

參考文獻

[2]. “PEM Fuel Cell Development in ITRI”, Energy and Resources Laboratories Industrial Technology Research Institute.

[83]. 陳韋任， “燃料電池用導電雙極板之碳奈米管/酚醛樹脂奈米複合材料備製及其性質研究”，私立中原大學機械工程研究所，2004.

[8]. 王智微，”台灣燃料電池產業發展現況”，能源報導，2006年8月

[13]. J. Larminie, A. Dicks, “Fuel Cell Systems Explained”, John Wiley, 2001

[16]. X.G. Li, S. Imran, International Journal of Hydrogen Energy, 30 (2005) 359.