Synchrotron radiography and tomography of water transport in perforated gas diffusion media

Abstract

Water transport in gas diffusion media (GDM) is investigated by synchrotron radiography and tomography. It is demonstrated that micro porous layer (MPL) cracks improve the water management in polymer electrolyte membrane (PEM) fuel cells. A further treatment by means of laser perforation is expected to enhance this effect. The radiography analysis reveals that water transport is practically not influenced by perforations applied only to the MPL. In contrast, perforations through the whole GDM (including the MPL) have a strong influence on the overall water transport behavior and are therefore considered for a deeper analysis. Performance measurements show a correlation between the perforation size and the fuel cell power density. An optimum is found for a perforation diameter of 60 µm. Synchrotron tomography analysis reveals that this optimum is due to an improved draining effect on the area around the perforation. Moreover, SEM and EDX analysis show a loss of PTFE on the GDM surface in the vicinity of the perforation due to the laser processing. The tomography images reveal water accumulations in this area that can be explained by the hydrophilic surface.