Locally confined membrane modification of sulfonated membranes for fuel cell application

We report a method which protects sulfonated hydrocarbon based proton exchange membranes at the interface between active and non-active area and in the gas inlet/outlet areas, where stresses are maximal during fuel cell operation. The sensitive membrane regions are subjected to a locally confined heat treatment using a stainless steel frame, under which desulfonation and/or crosslinking reactions occur. While modifications in air limit the reaction temperature to 180°C, inert atmosphere allows to raise the temperature and thus to shorten the necessary reaction time from 24h to less than 30min. Membranes are prepared from a commercially available copolymer (SES0005, Aquafone^TM), which has a high IEC (2.08meqg^-1) and a water uptake of 64%. As expected, modified membranes show reduced IEC values, reduced water uptake, and increased dimensional stability. Catalyst coated membranes (CCMs) are assembled into single cells for fuel cell testing. A membrane modified on all edges shows a stable performance in H₂/air fuel cell operation and an H₂ crossover current density of 0.52mAcm^-2, while a membrane modified only on two edges fails within 50h. Tensile and fuel cell tests show that the interface between modified and pristine area is not the preferred breaking point.