The Influence of Porous Transport Layer Modifications on the Water Management in PEM Fuel Cells

In this study, the influence of modifications of the porous transport layer PTL on the water management in PEM fuel cells is investigated. Laser perforation and milling are used to locally remove either the whole PTL or only the micro porous layer in the PTL. The changed dynamics and steady state distribution of the liquid water are visualized both in plane and through plane using synchrotron radiography and ESEM liquid water imaging. The observed effects are correlated with in situ performance characteristics, pre assembly and post mortem analysis to examine on the beneficial and obstructive effects of the modifications. The pre assembly analysis reveals that laser perforation results in PTFE loss in nearby regions. Hydrophilic regions around the holes are observed in both ESEM liquid water visualization and synchrotron radiography which results in a good performance at dry conditions but serious flooding at high humidification conditions. Machined perforations show beneficial effects in the in situ performance characteristics at high humidification conditions. A draining of the vicinity of the perforations is observed which results in an improved oxygen diffusivity. Water balancing and synchrotron visualization indicate that under the analyzed operating conditions the MPL increases the humidification of the Membrane Electrode Assembly on the one hand but creates an additional diffusion barrier by liquid water in the interface between the cathode catalyst layer and the MPL on the other han