3D Imaging of Polymer Electrolyte Fuel Cell Electrodes

Abstract

The degradation of Polymer Electrolyte Fuel Cell (PEFC) electrodes was examined by electrochemical and 3D imaging methods. A potential cycling test was conducted with a commercial catalyst coated membrane (CCM) where the cathode side of the cell was subjected to a potential square wave of 0.6V and open circuit voltage. After 24000 cycles, the PEFC performance remains nearly unchanged except for minor current losses in the low current regime. According to hydrogen under potential desorption measurements the electrochemically active Pt area decreases to 25% of the initial value. Synchrotron-based X-Ray tomography of the CCMs yields thickness distributions of catalyst layers and the membrane. A bubble like structure of the cathode layer is observed. Focused Ion Beam/Scanning Electron Microscopy-serial sectioning was employed to determine the pore structure of the cathode. The porosity before and after degradation was almost unaltered by the cycling test. TEM lamellas of the pristine and degraded cathode catalyst layers show an increase of the Pt particle size from 2.2nm to 4.6nm. Under the given conditions, an increase of hydrogen permeability across the membrane and a loss of Pt surface area are the predominant degradation mechanisms.