Tracking the evolution of mechanical degradation in fuel cell membranes using 4D in situ visualization [article]

Mechanical degradation occurs in fuel cell membranes due to the dynamic environmental conditions of operational duty cycles, and is regarded as a critical determinant of fuel cell durability and lifetime. Imaging-based failure analysis is typically employed to characterize structural and morphological aspects of the degradation, and 3D visualization capability of X-ray computed tomography is effectively expanding the scope of this analysis. This work further leverages the additional non-destructive and non-invasive attributes of this visualization technique to capture 4D information pertaining to the evolution of mechanical degradation in fuel cell membranes. A custom fuel cell fixture is utilized to periodically track identical membrane locations during the course of its mechanical degradation, which is generated through an accelerated stress test. The predominant fatigue-driven membrane crack development process is found to proceed non-linearly in time and is spatially concentrated under the uncompressed channel regions. Membrane cracking location is shown to be strongly correlated with beginning-of-life MEA defects, namely, electrode cracks and delamination. In situ crack propagation rates are quantified and the presence of a ‘crack closure’ effect during mechanical membrane degradation is demonstrated. Unlike crack initiation, crack propagation in the membranes does not appear to be significantly influenced by electrode morphology.