Unveiling the long-term degradation mechanisms of the sealing structures for durable PEM fuel cells by ex situ accelerated stability evaluation of a membrane electrode assembly

Abstract

The membrane electrode assembly (MEA) in proton exchange membrane fuel cells (PEMFCs) should be sealed with a robust frame for the long-term stability and performance of the fuel cell stacks. In this study, we investigated the long-term degradation mechanism of MEA frames containing proton-exchange membranes under the influence of various acceleration factors present in an actual fuel-cell operating environment using an ex situ accelerated lifespan evaluation method. The stability of the membrane-containing MEA frames is evaluated in terms of peel strength. We quantified the effects of water, temperature, and acidity, which are the main factors in an actual operating environment, on the long-term degradation of the MEA frame. Long-term exposure of the MEA frames to high temperatures in aqueous environments caused significant deterioration of their long-term durability. This deterioration was attributed to the weakening of the cohesive interactions between the ionomer chains in the Nafion membrane, which was accelerated in a strongly acidic environment. Furthermore, high temperatures and lower pH levels enhanced the glass transition of the ionomers and significantly increased the ion cluster area, increasing the free volume of the membrane layer and consequently reducing the long-term stability of the MEA frame. This study elucidated the underlying failure mechanisms of MEA frames containing membranes during fuel-cell operation and highlighted the influence of specific acceleration factors on the degradation of the frame-sealing structure, providing important guidelines for future consideration.