A New Crosslinked Sulfonated Polystyrene for Proton Exchange Fuel Cell Membrane

A series of crosslinked sulfonated polystyrene (SPS) membranes with different degree of sulfonation (DS) were prepared in the presence of phosphorous pentoxide-methanesulfonic acid (PPMA) in the ratio of 1:10 by weight via the condensation reaction between the sulfonic acid groups and the activated hydrogen atoms of SPS. The crosslinking reaction was confirmed by H-1-NMR and Fourier transform infrared spectrometry. In comparison with uncrosslinked SPS membrane, the crosslinked one showed much higher thermal stability as the degradation temperature increased from about 200 to 300 degrees C, lower but enough ion exchange capacity (IEC), lower water uptake, and lower swelling ratio. Moreover, the crosslinked SPS membranes still maintained high proton conductivity (3.3-6.1 x 10(-2) S cm(-1)) and keep good shape at room temperature in 100% relative humidity. The relationships among crosslinking time, crosslinking ratio, DS and membrane properties are discussed.