Understanding Mechanisms of Membrane Degradation in Membrane Electrode Assemblies with Ultra-Low Platinum Loadings

Abstract

Further commercialization of fuel cell technology remains to be hindered by the challenges encountered to fulfill the DOE cost, performance, and durability targets for automobile applications. In order to meet performance targets, platinum (Pt) continues to be the catalyst of choice for both electrodes. However, in order to meet the 2020 DOE cost target of $14/kWnet total Pt loadings need to be reduced to less than 0.125 mgPtcm- 2 while maintaining sufficient performance. In this work, we will develop a better understanding about the mechanisms of membrane degradation in membrane electrode assemblies (MEAs) as a function of catalyst loading. Specific emphasis were devoted to ultra-low Pt loadings, i.e., <0.1 mgPt cm-2, with symmetric anode and cathode loadings verified via X-ray fluorescence (XRF). Established accelerated stress tests (ASTs) were utilized to study chemical membrane degradation in MEAs using ion chromatography of effluent water samples collected at various times for the quantification of fluoride emission rates (FER). Membrane thinning was characterized via hydrogen crossover measurements as well as scanning electron microscopy (SEM) and X-ray computed tomography (XCT). Additionally, FER was probed as a function of varying testing conditions, e.g., temperature, relative humidity.