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Abstract
A series of composite membranes based on sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) comprising phosphotungstic acid (PWA) were fabricated and investigated as polymeric electrolytes for hydrogen/oxygen fuel cell (PEMFC) applications. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) matrices were first sulfonated to different extents to determine the maximum possible sulfonation degree, which ensures the highest proton conductivity as hydrolytic stability was not sacrificed. Subsequently, 20 wt% of PWA as a strong solid super acid was added into sulfonated polymeric matrices. Prepared composite membranes were characterized for their different properties including water uptake capacity, proton conductivity, and hydrolytic stability. The results of conductivity measurements revealed that in the presence of PWA molecules the proton conductivity of SPPO membranes with sulfonation degree of 40% was improved from 1.82 × 10−2 S cm−1 to 2.57 × 10−2 S cm−1 at 25°C. The improved proton conductivity of the SPPO/PWA composite membranes was attributed to the possible interaction of the hydronium molecules with sulfonate groups on SPPO chains as well as the PWA particles. Moreover, it was found that prepared PWA-filled ionomers (SPPO-40) were able to provide high proton conductivity (0.08132 S cm−1) even at elevated temperature ranges (120°C) as well as hydrolytic stability. Fuel cell performance tests showed that SPPO-40/PWA-20 nanocomposite membranes were able to provide 64% higher power output compared to corresponding pristine SPPO at 80°C. Owing to the favorable properties of high proton conductivity, high power density, ease of preparation, and low cost, SPPO/PWA composite membrane could be considered as a promising polyelectrolyte for moderate temperature PEMFC applications.