Degradation of Fuel Cell Materials Investigated by Atomic Force Microscopy

Kurzfassung

In this contribution the ability of atomic force microscopy (AFM) for investigation of fuel cell components and determination of their degradation is demonstrated. In particular the mapping of adhesion force and dissipation energy of surfaces analyzed by an advanced material sensitive AFM technique - the HarmoniX™-mode (Bruker Corp.) - has been used as a measure for the relative polytetrafluoroethylene (PTFE) content of surfaces. Differently operated microporous layers (MPL) of commercial gas diffusion layers (GDL) have been investigated before and after operation and were compared to reference samples. The degradation of the cathode material compared to the anode was found to be higher. Another example for exploring the potential of AFM is the investigation of a cell with a segmented anode flow field. The relative change of surface properties at MPLs detected with AFM analysis was compared to the direct measurement of PTFE content by infrared spectroscopy (FTIR-ATR) and a good correlation of both results has been found for the analyzed segments. The ionically conductive structure of electrolyte membranes has also been investigated by conductive AFM in humid environment. High resolution images show an heterogeneous conductivity with non-conductive regions even after fuel cell operation. Sharply defined areas with same mean magnitude of current at the surface indicate the presence of an interpenetrating network of ionic channels connected beneath the surface. A correlation with surface properties measured by the PeakForce Quantitative Nanomechanical Property Mapping (QNM™) is observed.