Highly Proton-Conductive Sulfonated Aromatic Polymers for Medium-Temperature Proton Exchange Membrane Fuel Cells

Sulfonated aromatic polymers have attracted lots of attention owning to their high thermal and chemical stability, excellent mechanical strength, low fuel permeability and easy manufacturing. For these reasons, sulfonated aromatic proton exchange membranes (PEMs) have been recognized as promising electrolyte materials. However, proton conduction in the majority of randomly sulfonated ionomers is too low as compared with Nafion (Dupont (TM)) which have been currently widely used. Redesign of the polymer chemical structure is demanded for improving the properties of ionomers at elevated temperatures and reduced relative humidity (RH). This paper embarks from sulfonated aromatic block copolymers, grafted sulfonated aromatic copolymers and locally and densely sulfonated aromatic copolymers, and reviews the relationship between the structure and proton conductivities of sulfonated aromatic polymers. Meanwhile, in order to improve the proton conductivities and other properties, inorganic proton conductors or acidic inorganic materials are doped into membranes to prepare composite membranes.