Andrea Haug

Analysis of aged Polymer Electrolyte Fuel Cell (PEFC) components by non traditional methods

The ageing of microporous layers (MPL) of fuel cell gas diffusion layers has been quantitavely analyzed using a special atomic force microscopy technique, namely the so-called HarmoniX technique. From the change of mean adhesion force under dry and wet conditions an increased loss of polytetrafluoroethylene (PTFE) at the cathode was found. With ionic current measurement in tapping and contact mode by AFM, activated Nafion was investigated before fuel cell operation with high resolution and individual ionic channels were imaged in one cluster. These measurements were compared to the current distribution of membranes after 1600 h of fuel cell operation under OCV. Distinct current levels were found which demonstrate the existence of an interpenetrating ionic network with different branches not directly connected at the surface. SEM/EDX investigations of the specially designed fuel cells indicate an important role of platinum in degradation of membranes.

Investigation of Local Degradation Effects

Degradation processes in PEFC lead to insufficient life-time which is one of the crucial problems hindering mass market penetration of fuel cells. The degradation rate depends strongly on the operating conditions, of fuel cells and in addition the operating conditions can vary significantly along the flow path. Therefore, at DLR the degradation processes are investigated with locally resolved in-situ methods which are combined with locally resolved ex-situ characterizations. The combination of the in-situ and ex-situ methods allows to quantify and to identify the degradation processes. Based on the locally resolved investigations the relation of the degradations processes with the operating conditions and consequently the identification of the causes and effects of degradation processes is discussed for electrodes and gas diffusion layers.

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.