Alexander Bauder

Nanoscale Investigation of Nafion Membranes after Artificial Degradation

In this contribution we report on the nanostructure and conductivity of freshly prepared as well as artificially degraded Nafion membranes investigated by contact atomic force microscopy (AFM),conductive AFM, and pulsed force-mode (PFM)-AFM. The different techniques can provide complementary information on structure and conductivity. Conductive AFM gives information about the internal structure of ionic clusters during current flow. High resolution current images of the membrane were used to directly compare the measured nanostructure of the single conductive channels with model predictions from the literature. The influence of H2O2 treatment as a method for artificial degradation is investigated. The analysis of adhesion forces demonstrates a significant change of thesurface properties with different membrane treatment. Topography and adhesion measurements clearly show materials changes with high resolution and correlate with changes in conductivity distributions.

Atomic Force Microscopy Investigation of Polymer Fuel Cell Gas Diffusion Layers before and after Operation

The ageing of microporous layers (MPL) of fuel cell gas diffusion layers has been analyzed using a special atomic force microscopy technique. The mean local adhesion force on the surface as well as the energy dissipation on the same area has been used as a measure for changes of surface properties corresponding to ageing of the MPL. The samples have been studied before and after fuel cell operation. In all cases, the changes due to operation are stronger on the cathode compared to the anode. The results from measurements under comparably dry and wet conditions are consistent with an increased loss of polytetrafluoroethylene (PTFE) at the cathode which leads to a hydrophobicity loss.