Investigation of Gas Diffusion Layer Perforations on the water transport in PEM fuel cells with synchrotron imaging

Abstract

With increasing performance of PEM fuel cells water transport in Gas Diffusion Layer becomes more and more a critical aspect. High humidity conditions, which are favoured for proton conducting membranes, enhance the problem of water condensation and removal. A well designed GDL can help to avoid critical operation conditions, which can decrease performance and lifetime. One way of possible improvement is to add artificial pore paths to the porous GDL structure. Vertically arranged paths can guide liquid water more easily from the electrode to the channel due to the lowered capillary pressure. To achieve this, laser perforation and mechanical milling were used to apply perforations to the GDL. From former investigations, it is known that natural cracks in Micro Porous Layer (MPL) serve as transport ways for liquid water. GDL with separately perforated MPL are considered in this work as well. For investigation of liquid water transport, synchrotron radiography and tomography have proven to be suitable measurement techniques. Thus, water transport dynamics and 3D water distribution were analyzed regarding to the influence of the different perforation techniques. It showed that perforations fill with water under high humidity conditions and may serve as transport ways, as well. By comparing laser and mechanical treated GDL, a difference in the filling behaviour was observed. Laser treated material looses PTFE content due to high temperatures and the perforation area gets hydrophilic, whereas mechanical treatment showed less influence to the surface properties of the surroundings. This result was proved by EDX measurements (F distribution) and by hydro head analysis (influence on water transport behaviour). Finally, performance tests showed the difference between the perforation techniques and different perforation diameters. It has been proven that perforating of GDL enhances the performance compared to unperforated material, especially under high humidity conditions.