奈米管複合高分子中高溫質子交換膜

Sulfonated Titanium Oxide Nanotube Composite for High Temperature Proton Exchange Membrane Fuel Cell (PEMFC)

李亮儀(Liang-Yi Li)

指導教授 ： 諸柏仁

國立中央大學/理學院/化學系/碩士(2008年)

摘要

質子交換膜燃料電池在高溫操作下可以降低CO 毒化陽極觸媒，提高電化學反應速率…等優點，但是由於目前商業化的 Nafion 薄膜在高溫操作下，質子傳遞所賴以依附的水分子容易流失，造成導電度急速下降，因此在薄膜中添加入一些保水性無機奈米粒子，可以使薄膜在高溫下仍可保存水分，因此可以維持較高的導電度，以獲得較好的發電效能，甚至在低濕度的環境操作下也會比單純使用 Nafion 薄膜所組成的燃料電池的效能還要好。本研究中使用管狀結構的二氧化鈦奈米管，並於其表面修飾磺酸官能基，帶有磺酸官能基的二氧化鈦奈米管（sTNT）具有良好的保水性質，將之摻入sPEEK 高分子中，形成有機/無機複合薄膜，此質子交換膜具有極
佳的相容性，突破了傳統有機/無機混合物的不均勻性及相分離問題。另一方面，磺酸化二氧化鈦奈米管的管狀結構及無機物表面磺酸根的親水性，而且無機物上的磺酸根與高分子上的磺酸根產生的交互作用力，使水分子在有機/無機的界面間產生較強的鍵結，此結果使薄膜在高溫下更展現出極佳的保水性而使導電度得以維持，特別是分散性較好的 5wt%sTNT/sPEEK 複合薄膜，其導電度在100oC、60%RH 的環境下仍有10-2 S/cm的導電度。
在實驗中也發現 sTNT 的磺酸化程度與薄膜的導電度並未呈現正比關係，含 05sTNT ( IEC = 1.4mmol/g ) 薄膜組成具有較高的導電度，但是含較高磺酸化程度的08sTNT ( IEC = 1.68mmol/g ) 薄膜，其導電度卻比較低磺酸化程度的05sTNT/ sPEEK 薄膜低，此結果顯示，無機物的磺酸根與sPEEK 的磺酸根之間的分佈會產生不同的微結構型態，進而影響水分脫附的程度，改變導電度行為。

關鍵字

質子交換膜燃料電池 ； 磺酸化二氧化鈦奈米管 ； 磺酸化聚二醚酮

並列摘要

Numerous advantages are identified in operating fuel cell at elevated temperature, which include better tolerance towards CO poisoning, higher electro-chemical kinetics, and promising of higher output power. However, the output power of PEMFC using state of art proton exchange membrane is dramatically reduced due to increase of internal resistance from the loss of water from these membranes as the temperature increases to above 80C. Currently the proton conduction of the perfluorosulfonic acid ( PFSA , such as Nafion ) membranes rely on water for proton transport. Water evaporation means a dramatic decrease of proton conductivity and, consequently loss of fuel cell performance. Developing new proton exchange membrane suitable for PEM fuel cells (PEMFC) to operate at temperatures above 150 °C becomes the new challenge in this field which is critical for the future of fuel cell technology.
Present study examines the effect of sulfonated poly aryl ether ketones (sPAEK)s composited with sulfonated inorganic nanoparticle for high temperature purpose. Sulfonated titanium oxide nanotube (sTNT) displayed excellent water retention capability which preserved certain amount of water in temperature higher than the normal boiling temperature. As a result, composite membrane delivered impressive conductivity surpassing sPAEK membranes without using the nano-composite and other membranes operating at low humidity conditions or at elevated temperature above 110 C. These nanocomposite proton exchange membranes were prepared from sulfonated poly(ether ether ketone) (sPEEK) and physically blended with various amounts of sulfonated titanium oxide nanotube (sTNT) using common solvent. Fucntions of the inorganic moiety are two folds, first it improves thermal stability and provided tougher strength at elevated temperature. Secondly, it shows residual water content even above 140C, which facilitate proton transport. From low moisture content (R.H.=20%) to saturated moisture (RH=100%) conditions, proton conductivity of the membrane containing sTNT is higher than pristine sPEEK. This is especially the case with 5wt% sTNT composite, where the most homogeneous morphology (best inorganic dispersion) is observed. For 5wt% sTNT/sPEEK composite membrane the porton conductity reached above 10-2 S/cm at 100oC, 60%RH. These membranes display excellent proton conductivity when temperature is higher than 100oC, and continue to increase with increasing temperature while other membranes either lost the proton conductivity or yield to severe swelling and loss of membrane strength under elevated temperature. A unique proton conducting behavior is also identified in these composite membranes where proton migration along the tubular inorganic surface is assisted with the presence of a small amount of water retained in the tube.
Since the IEC ( ion exchange capacity ) content of these membranes depend on the degree of sulfonation on both the sPEEK and on sTNT, it is important to find out if increasing the degree of sulfonation on TNT surface would improved the conductivity further. This is easy to do, since the degree of sulfonation on the TNT surface can be controlled by varying the amount of sultone. The results shows, in spite of the higher IEC value, the membrane using TNT with higher degree of sulfonation (0.8sTNT. IEC = 1.68mmol/g) delivered worse proton conducting behavior than that from lower degree of sulfonation (0.5sTNT, IEC = 1.4mmol/g). These results suggested the proton conductivity does not depend on IEC alone, but the membrane morphology with well connected conducting channel and suitable distribution of sulfunated group within the membrane are also important factors in contribution towards proton conductivity.
These membranes are promising as high temperature PEM fuel cell materials. The feasibility is demonstrated by fuel cell performance operating under temperature above 120C.

並列關鍵字

sTNT ； proton exchange membrane fuel cell ； sPEEK

參考文獻

112.呂怡萱，「二氧化鈦奈米管於染料敏化太陽能池之探討」，國立中央大學，碩士論文民國95年

78. Je-Deok Kim, Toshiyuki Mori, and Itaru Honma; Journal of The Electrochemical Society 2006,153 (3) A508-A514

107. Roger Mueller , Hendrik K. Kammler , Karsten Wegner and Sotiris E. Pratsinis;

27. Yang, C., Srinivasan, S., Arico`, A. S., Creti, P., Baglio, V., Antonucci, V.;

71. Yang, C., Srinivasan, S., Arico`, A. S., Creti, P., Baglio, V.,Antonucci, V. ; Electrochem. Solid-State Lett. 2001, 4, A31.