Fabrication of poly (m-Tolyloxy-co-4-pyridinoxy phosphazene) based proton exchange membranes for fuel cell applications

Official URL: http://risc01.sabanciuniv.edu/record=b1558945 (Table of Contents)

Nafion® is the most commonly used commercial proton-exchange membrane for polymer electrolyte membrane fuel cells (PEMFCs) due to its excellent thermo-mechanical properties. The main drawbacks of Nafion® membranes are their temperature dependent conductivity, degradation at temperatures greater than 80 ºC and relative humidity less than 100% and also high cost, hence it is necessary to find the alternative membranes for PEMFC. Polyphosphazenes are a potential candidate owing to their ability to incorporate unlimited side-groups and their good thermal and chemical stability. In this work, three poly (m-tolyloxy-co-4-pyridinoxy phosphazene)s with varying heteroatom containing and not containing aryl side chains in varying ratios were studied. Through sulfonation the sulfonic acid group which promotes proton conduction was incorporated. Different parameters such as effect of temperature, time and varying amounts of each side groups of the polymers on the sulfonation process were investigated and the results reported. After sulfonation membranes with thicknesses in the range of 80-120 μm were obtained through solution casting and later on characterized. Structural characterizations by use of NMR (1H, 13C and 31P) and FTIR were carried out before and after sulfonation in order to check the post process changes. FTIR revealed extra peaks at 1300 cm-1 that belonged to the sulfonic acid groups. DSC and TGA were used to check the membranes’ thermal properties while the mechanical stabilities was investigated using the DMA. The resultant membranes were then evaluated for the basic PEMFC relevant properties such as IEC, water uptake and proton conductivity and the results compared to those of Nafion® 115. In this work, we reported IEC values of as high as 1.07 meq/g which was comparable to that of Nafion® 115 (0.91 meq/g) in the literature. Conductivity of the membranes varied depending on the sulfonation parameters and values obtained were comparable to the membranes in the literature and Nafion® 115 as well.