Progress in ionic organic-inorganic composite membranes for fuel cell applications

Over the past decade, organic-inorganic composite ionic membranes have gained tremendous attention for use in medium temperature fuel cells. The addition of a functional or nonfunctional inorganic into the organic material is usual practice in proton exchange membranes to improve their thermal stability and performance. In the development process, perfluorosulfonated membranes and their composites with inorganic materials dominate and show better thermal, mechanical and chemical stability, and proton conductivities at intermediate temperatures with low fuel drag. Concurrently, composites of hydrocarbon polymers, such as poly(arylene ether ketone)s, poly(benzimidazole)s, poly(arylene sulfone)s, poly(vinyl alcohol) etc., have been developed as alternatives to perflurinated membranes. The present review addresses the basic route used to synthesize these composite membrane materials. The main emphasis has been given on the preparation procedures of inorganic materials, their modifications and composites with perfluorinated and hydrocarbon polymers. The properties are addressed with respect to fuel cell applications.