Inorganic–Polymer Composite Membranes for Proton Exchange Membrane Fuel Cells

Composite membranes consisting primarily of a polymer and an inorganic proton conducting particle or a proton conducting polymer containing inorganic particles for use as proton exchange membranes in low and intermediate temperature fuel cells are reviewed. The chemistry of major inorganic additives that have been used is described in terms of their structure and intrinsic ability to conduct protons. Composites are classified in terms of four main classes: inorganic proton conductors suspended in inert polymers; inorganic particles added to extend polymeric ionomers; inorganic proton conductors blended with polymeric ionomers; and polymer acid complexes between basic polymers and acidic inorganic particles.