Mechanical failure of a polymer electrolyte membrane (PEM) such as pin-hole and delamination has been identified as a major degradation source in a PEM fuel cell. The hydration/dehydration cycles of a membrane during the fuel cell operation, and the resulted mechanical stress, are in general responsible for the mechanical failures. For example, the cyclic mechanical stressor has shown a significant role in propagating a crack through the thickness of a membrane [1], although there is also the synergistic acceleration from the chemical stressor [2]. It is of interest to thoroughly investigate the mechanical behaviors of a membrane under in-situ cyclic conditions, so that alleviating strategies focusing on the fuel cell operating conditions could be developed.

We have interfaced a two-dimensional transient fuel cell transport/performance model in Comsol [3] with a viscoelastic-plastic membrane mechanical model in the fuel cell geometry [4]. Using the combined model we have studied the impacts of dynamically cycling hydration, current and voltage on a membrane [5]. Furthermore, we have developed a model-based method to predict the crack propagation rate. It is expected that the crack propagation rate could be used as a metric to differentiate various dynamic driving cycles from the mechanical durability aspect, thereby creating a pathway to a transfer function for mechanical durability. The modeling results will be validated with RH cycling data. The role of the chemical stressor will also be discussed in using this mechanical durability transfer function.

References:

[1] G, Ding, M. Santare, A. Karlsson, and A. Kusoglu, “Numerical evaluation of crack growth in polymer electrolyte fuel cell membranes based on plastically dissipated energy”, Journal of Power Sources 316, 114-123 (2016).

[2] A. Kusoglu and A. Weber, “Electrochemical/Mechanical Coupling in Ion-Conducting Soft Matter”, Journal of Physical Chemistry Letters 6, 4547−4552 (2015).

[3] A. Goshtasbi, P. Garcia-Salaberri, J. Chen, K. Talukdar, D. Sanchez, and T. Ersal, "Through-the-Membrane Transient Phenomena in PEM Fuel Cells: A Modeling Study." Journal of The Electrochemical Society, Under Review.

[4] N. Khattra, A. Karlsson, M. Santare, P. Walsh, and F. Busby “Effect of time-dependent material properties on the mechanical behavior of PFSA membranes subjected to humidity cycling”, Journal of Power Sources 214, 365-376 (2012).

[5] M. Hasan, A. Goshtasbi, J. Chen, M. Santare, and T. Ersal, "Model-Based Analysis of PFSA Membrane Mechanical Response to Relative Humidity and Load Cycling in PEM Fuel Cells." Journal of The Electrochemical Society, 165(6), F3359-F3372 (2018).