Improved water transport in natural and artificial pore paths of gas diffusion layer in PEM fuel cells

Abstract

Gas diffusion layer in PEM fuel cells have to fulfil many tasks: high electrical and thermal conductivity, gas and water transport. Different pore sizes and pore geometries in gas diffusion layer influence these parameters. For high current densities, water agglomerations in the porous medium limit the fuel cell performance. The geometry of the carbon fibre substrate and natural cracks in the micro porous layer form preferred water pathways through the porous structure. Synchrotron radiography and tomography studies prove the importance of these pore paths for the overall water distribution. Regarding the flow field design it is found that these water paths cause a draining effect, which transports water from under the land to the gas channel. For further improvement a higher and more regular distribution of cracks is necessary. To achieve this, laser perforation based on and mechanical milling techniques were applied. With this treatment a higher overall performance has been obtained due to the improved water transport. This has been proven by synchrotron imaging.