(Invited) Limits of Polymer Electrolyte Membranes

Abstract

Since their introduction in the 1960’s polymer electrolyte membranes, PEMS, for fuel cells have been extensively studied. Hundreds if not thousands of polymer systems have been synthesized and characterized to improve the critical properties of conductivity, chemical and mechanical durability as well as the lesser important properties of water and gas transport. It is well accepted that these properties are highly dependent on the chemistry of the polymer electrolyte backbone as well as the functional groups and how they organize on the molecular scale. Many models have been used to frame these properties to fit experimental data. What is done less-often is to use the models to then establish the limits of these. Using the conductivity of their small-molecule analogies, triflic acid for PFSA’s and benzene sulfonic acid for hydrocarbons we set limits on conductivity and permeability. Finally we will also look at how the two most common strategies of increasing PEM performance; increasing charge density and acid strength, are limited by mechanical and chemical durability requirements, respectively.