Sulfonated poly(arylene ether sulfone) membrane containing sulfated zirconia for high-temperature operation of PEMFCs

A new composite membrane that consists of sulfonated poly(arylene ether sulfone) (SPES) and a highly functionalized inorganic filler of sulfated zirconia (s-ZrO(2)) was synthesized and evaluated for enhancement of water retention as well as proton conductivity at high temperatures above 120 degrees C in the absence of water. Since the SPES has less hydrophobic/hydrophilic difference between the polymer backbone and -SO(3)H ionic groups, the proton channels are relatively small and not easily distributed, which results in no significant change at highly saturated conditions. Therefore, the effective interconnection between the -SO(3)H ionic groups and bound water adsorbed on the surface of the s-ZrO(2) is the key in achieving a higher proton transfer for PEM fuel cells at high temperatures above 120 degrees C. Analysis by small angle X-ray scattering (SAXS) of recast membranes showed that SPES random copolymers with various s-ZrO(2) contents have a similar ionic cluster size and less pronounced phase separation regardless of the dry/swollen condition of the membrane. However, the phase images obtained by atomic force microscopy (AFM) showed that the connectivity of ionic groups varies, depending on the content of s-ZrO(2) in the polymer matrix. Larger and more interconnected hydrophilic regions were found with the SPES membrane when there was no significant particle aggregation in the hydrophilic moieties of the polymer matrix. In this study, the composite membrane with 5 wt% s-ZrO(2) had the highest proton conductivity at 120 degrees C due to better ionic interactions as well as the presence of bound water combined with the -SO(3)H ionic groups.