In Situ X-ray imaging of HT-PEMFC hot-pressing using contrast enhancement

A contrast enhancement agent is used to visualise phosphoric acid penetration and distribution in high-temperature polymer electrolyte membrane fuel cells. This new method is demonstrated in the investigation of hot-pressing parameters on phosphoric acid penetration and distribution. In situ radiography of the hot-press process showed acid plumes breaking through the catalyst layer, microporous layer (MPL) and gas diffusion layer (GDL). The phosphoric acid volume and distribution within the MPL and GDL are quantified, and their dependence on hot-press pressure, duration and compression control are analysed. Increasing hot-press pressure and duration was found to increase acid penetration and delamination of the membrane and catalyst layers. The absence of a compression control gasket also led to significant infiltration into the MPL and GDL. Penetration occurred first at the anode for all tests, which was attributed to a higher number of cracks and greater degree of crack connectivity. Phosphoric acid entered the MPL and GDL either through initial breakthrough of the catalyst layer, or from acid pooling on the GDL surface and being compressed into the fibres. This work provides a novel method to improve visualisation of phosphoric acid and highlights the acid loss mechanisms resulting from hot-press conditions.