The gas diffusion layer (GDL), which also provides contact to the electrochemically active components, has to achieve the passive management of the water balance. The adjustment of the hydrophobicity of the GDL is crucial for stable operation, and non-uniform hydrophobicity has already been shown to be advantageous.
Typically, gas diffusion electrodes for polymer electrolyte fuel cells (PEFC) consist of conductive medium, either a carbon based powder in the microporous layer (MPL) or carbon felt/fibres/cloth in the macroporous backing, and a hydrophobicity impregnation agent like polytetrafluoroethylene (PTFE). The ratio of these components determines the hydrophobicity, which effects the performance. The MPL was modified by laser irradiation. The effect of the laser radiation on the MPL were characterized by x-ray photoemission spectroscopy, Raman and infrared absorption spectroscopy and correlated to the change in the hydrophobic properties.
In particular, non-uniform hydrophobicity was applied and also tested in PEMFC. The introduction of channels of reduced hydrophobicity leads to several benefits. The observed current density distributions became more homogeneous than that of MPL without additional modification. Thus, the area with extreme current densities decreases, resulting in a more homogeneous ageing and, consequently, in an improved lifetime. Moreover, this modification leads to distinct performance increase in certain combinations of CCM and GDL. As an additional finding, not every combination can be improved, or is even performing well.
Acknowledgements
The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303446 (IMPALA).