有機無機混成質子傳導膜於燃料電池的運用

Abstract

本論文中利用改質的碳材去解決燃料電池目前所面臨的困境，研究內容分為三大主軸:

1. 改質的活性碳於氫氣燃料電池上的運用 將活性碳導入質子傳導膜中可有效的提升其含水率、降低膨潤比與在低溼度下大幅度的提升離子導電度，水分子可以藉由活性碳的微孔與Nafion的離子團產生相互聯繫的奈米通道作傳遞，在低濕下依舊可以保有一定的水份，因此可以維持其良好的離子導電度。除此，堅固Nafion主鏈(特弗龍)與不易形變的活性碳造成活性碳複合膜擁有較好的機械性質。

2. 改質的活性碳於氫氣燃料電池上的運用 利用活性碳的高表面積和微孔與Nafion來製備一個低成本與高效能的高飽水複合膜，此複合膜具備較高的飽水率與良好的導電度可以被運用在氫氣燃料電池，利用此複合膜製備出來的燃料電池相對於商品Nafion 211有較好的放電特性。由電化學交流阻抗分析結果看來較好的結果在於複合膜的卓越的特性。

3. 低甲醇穿透率的磺酸化氧化石墨烯/Nafion複合質子交換膜 低甲醇的質子交換膜可以藉由簡單且有效率的分散磺酸化氧化石墨烯於Nafion製備而成，藉由黏度的變化去判別其分散的情況；成膜後，此複合膜具備低的甲醇穿透度、好的尺寸安定性與在低濕環性下較好的質子導電度。由小角度x光繞射結果顯示，此複合膜的離子通道大小確實因為氧化石墨烯的存在而有所縮小，在其機械強度有顯著的增加，甲醇燃料電池的放電結果顯示添加適量的磺酸化氧化石墨烯確實有助於放電性能的提升，且其放電特性並不會因為甲醇濃度的增加而下降，具有商業化潛能。

In this study, we focus on the modification of carbon materials and their application on fuel cells. 1. Highly hydrated Nafion/activated carbon hybrids The incorporation of highly porous activated carbon (AC) to Nafion membranes confers unprecedented levels of water uptake (4 times higher for 10 wt% AC compared to neat Nafion) at a minimal dimensional swelling and results in dramatic enhancements in ionic conductivity at low relative humidity. This behavior reveals the development of a robust network of water nanochannels formed by the carbon pores and the polymeric ionic domains which is structurally stabilized by the rigid Nafion backbone and the non-deformable AC particles.

2. Characteristics of high-water-uptake activated carbon/Nafion hybrid membranes for proton exchange membrane fuel cells A cost-effective and high-throughput method for producing high-water-uptake membranes is developed by combining high-porosity and superior-surface-area activated carbon with Nafion. The resultant activated carbon/Nafion hybrid composite exhibits high water uptake and an improved proton conductivity, which can be exploited in a proton exchange membrane fuel cell (PEMFC). This hybrid membrane displays a superior performance to that of the commercial Nafion 211 when used in fuel-cell measurements. Electrochemical impedance spectroscopy (EIS) is used to simulate the changes in resistance during the operation of the fuel cells and conclusively explains the improved performance of the composite membranes.

3. Sulfonated graphene oxide/Nafion composite membranes for high-performance direct methanol fuel cells An easy and effective method for producing low methanol-crossover membranes is developed by dispersing sulfonated graphene oxide (SGO) into a Nafion matrix. A SGO/Nafion mixture with low SGO content exhibits unique viscosity behavior and allows for better SGO dispersion within the Nafion. After film casting, the composite membranes show lower methanol and water uptakes, a reduced swelling ratio, improved proton conductivity in low relative humidity, and extremely high methanol selectivity, which can be implemented in direct methanol fuel cells (DMFCs). The regular backbone of the composite membrane shows a higher storage modulus, increased -relaxation (transition temperature), and improved tolerance to pressure during membrane electrode assembly (MEA). The small angle X-ray spectra indicate the shrinkage of the ionic clusters in the composite membranes, which thus reduce methanol crossover. The hybrid membranes applied to DMFCs demonstrate performances superior to that of the commercial Nafion115 in 1 M and 5 M methanol solutions.