4D imaging of chemo-mechanical membrane degradation in polymer electrolyte fuel cells - Part 1: Understanding and evading edge failures

Abstract

This work is a two-part article series on chemo-mechanical membrane degradation in fuel cells, wherein the present work in Part 1 investigates edge failure and Part 2 investigates failure within the active area of an edge-protected cell. Membrane electrode assembly (MEA) edges are sensitive regions that can cause premature failure. Here, two different MEA frame designs are implemented to study their robustness during a combined chemical/mechanical membrane degradation accelerated stress test. 4D in situ visualization by periodic, identical-location X-ray computed tomography is performed to understand and thus mitigate the design issues responsible for edge failures. Interfacial interaction of adhesive-containing polyimide gasket and MEA and non-uniform load distribution along MEA edges are identified as the two key contributors to premature edge failures, which introduce significant cell voltage decay due to permanent membrane deformation. Edge failure mitigation is demonstrated by using a non-adhesive sub-gasket along with increased gasket coverage area, which leads to: (i) delayed onset of edge failure; (ii) five times reduction in edge crack size; (iii) elimination of membrane tearing; and (iv) minimal impact of edge failures on cell performance, thus enabling a robust MEA edge wherein the performance-impacting failure is shifted to the more important active area regions. • 4D in situ visualization scheme is applied to study membrane failure at MEA edges. • Edge crack propagation at identical MEA locations is captured for the first time. • Edge failure occurs primarily due to non-uniform interfacial stress distribution. • A robust MEA frame design is demonstrated that can endure chemo-mechanical stress.