Hydrophobicity Patterning of Gas Diffusion Media and Performance in Polymer Electrolyte Fuel Cells

Kurzfassung

Polymer electrolyte fuel cells with their high gravimetric energy density face a water balance problem especially under variable loads, e.g. automotive operation: The excess product water needs to be removed from the fuel cell while maintaining a humidified membrane. The gas diffusion layer (GDL), which also provides contact to the electrochemically active components, is responsible for a passive water management of the cell. The adjustment of the hydrophobicity of the GDL is crucial for stable operation. In polymer electrolyte fuel cells they typically consist of conductive medium, either a carbon based powder in the microporous layer or carbon felt/fibres/cloth in the macroporous backing, and a hydrophobicity impregnation agent like polytetrafluoroethylene (PTFE). The ratio determines the hydrophobicity and thus the performance. Modifications of the hydrophobicity were applied with the goal to form a structured, non-uniform wettability of the gas diffusion media, thus introducing more hydrophilic evasion pathways for water while maintaining more hydrophobic areas. It is shown, that these modifications can result in considerable performance improvement and more homogeneous current density.