The chemical and structural nature of proton exchange membrane fuel cell properties

The chemical and structural (morphological) features of proton exchange membranes are directly tied to their fuel cell relevant transport properties. A large body of research has focused on characterizing the structure or investigating the properties of Nafion (R) and other proton exchange membranes, but few studies have linked chemical composition to membrane morphology, and resulting transport properties. This paper systematically discusses the key chemical and structural features of proton exchange membranes that impact properties critical for fuel cell applications. We focus our discussion on the fuel cell relevant transport properties of proton conductivity, methanol permeability, water diffusion coefficient, and electro-osmotic drag coefficient, using evidence from our work and from the literature to illustrate the connection between structure and properties in these materials. It is hoped that this document will serve as a guide to the rational, systematic design of new proton exchange membrane materials with improved properties.