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.

Contents
1 Introduction
2 Morphological phase-separation of PEMs
2.1 Sulfonated aromatic block copolymers
2.2 Pendant sulfonic acid of aromatic copolymers
2.3 Locally and densely sulfonated aromatic copolymers
3 Organic-inorganic composite PEMs
3.1 PEMs composited with inorganic solid proton conductor
3.2 PEMs doped with acidified inorganic particles
4 Conclusions and outlook