In order to understand the performance of PEM fuel cells, it is necessary to not only understand the structure but also the water dynamics in these materials over a large range of humidities, temperatures, and processing conditions. Proper water man­agement is critical to optimal fuel-cell performance. Many studies have focused on understanding the bulk-water transport and there has been a considerable effort to understand how this transport is related to the nanostructure of the membrane.

While bulk-water transport is an important aspect of fuel-cell operations, it is important to keep in mind that this macroscopic property is governed by the nano­structure of the membrane and, ultimately, the local-water dynamics within this structure. Researchers have used neutron spectroscopic techniques to investigate the local-water dynamics within the nanoscale ionic aggregates present in the material. In addition to understanding the dynamics and transport, the static and dynamic water concentration-gradient that is present across the MEA during fuel-cell operation is also a central piece of data for proper water management. Current neutron imaging techniques do not have the spatial resolution to map the water gradient across the thickness of the MEA during fuel-cell operation, but researchers have been able to use SANS techniques to elucidate this information in a clever way.

While the focus has mainly been on water, little effort has been spent on understanding the relationship between the water dynamics (both local and mac­roscopic) on the polymer-chain dynamics and fluctuations within, and of, Nafion®’s complex morphological features. Page and co-workers have used QENS and NSE techniques to address these issues.

The following sections summarize the work, to date, using QENS, SANS, and NSE to study the transport and dynamics in PEM materials, particularly Nafion®.