A study on the exhaust process of the product water in the PEFC by EDX mapping of a tracer

The present work addresses the clarification of the exhaust process of the product water in the polymer electrolyte fuel cell using a tracer. Magnesium acetate tetrahydrate and a surfactant (polyoxyethylene di-styrenated phenyl ether) are dissolved into distilled water to prepare the tracer. The magnesium tracer is painted on the separator or electrode (catalyst layer) side of gas diffusion layers (GDLs) and dried. After operating a cell with these GDLs, magnesium at the surface and cross-section of the GDLs is captured ex-situ by energy dispersive X-ray spectroscopy (EDX) mapping on scanning electron microscope (SEM) images. In the case of the GDL having micro-porous layer (MPL), water produced at the rib part electrode of the cathode is found to be transported to the interspace between the channel part MPL and electrode in liquid phase. A part of the water is possibly transported through the MPL to the channel in gas phase. The water accumulated at the interspace is also found to be exhausted through the MPL to the channel in gas phase. Moreover, the suppression mechanism of the flooding by the MPL is shown as follows. The MPL repels condensed water in the GDL substrate, preventing transport of the liquid water to the electrode, so that the water accumulates in the GDL substrate.