Polyphosphazene Membranes for Fuel Cells

Polyphosphazenes possess numerous properties that are attractive for PEM fuel-cell applications, including thermal and chemical stability and the unlimited possibility for side-group functionalization. There are some impressive results in the literature, in particular where sulfonated polyphosphazenes are used in a direct methanol fuel cell. There is much less data on polyphosphazene fuel-cell membranes with phosphonic acid or sulfonimide side groups, but preliminary physical and transport property data on these materials is encouraging. Clearly, more work is needed to truly exploit the full potential of this important class of inorganic polymers, including the development of new polymer synthesis schemes and the use of combinatorial methods to screen the unlimited number of side group-substituted polymers. Herein an overview of prior research on the synthesis and use of acid-functionalized polyphosphazenes in proton exchange membrane fuel cells is presented.