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The influence of porous transport layer modifications on the water management in polymer electrolyte membrane fuel cells
In this study, the influence of modifications of the porous transport layer (PTL) on the water management in polymer electrolyte membrane 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 liquid water distribution is visualized 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 analysis reveals that laser-perforation results in PTFE loss and hydrophilic regions 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 ionomer 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 hand.