Mechanisms of proton conductance in polymer electrolyte membranes

We provide a phenomenological description of proton conductance in polymer electrolyte membranes, based on contemporary views of proton transfer proce sses in condensed media and a model for heterogeneous polymer electrolyte m embrane structure. The description combines the proton transfer events in a single pore with the total pore-network performance and, thereby, relates structural and kinetic characteristics of the membrane. The theory addresse s specific experimentally studied issues such as the effect of the density of proton localization sites (equivalent weight) of the membrane material a nd the water content of the pores. The effect of the average distance betwe en the sulfonate groups, which changes during membrane swelling, is analyze d in particular, and the factors which determine the temperature dependence of the macroscopic membrane conductance are disclosed. Numerical estimates of the specific membrane conductivity obtained from the theory agree very well with typical experimental data, thereby confirming the appropriateness of the theoretical concepts. Moreover, the versatility of the models offer s a useful and transparent frame for combining the analysis of both experim ental data and the results of molecular dynamics simulations.