Mechanical failure of the polymer electrolyte membrane in the form of cracks, pin-holes and delamination has been identified as a limiting factor in the durability of the fuel cell. The hydration/dehydration cycling of the membrane during the fuel cell operation, and the resulting mechanical stress, are in general responsible for the mechanical failures. For example, the cyclic mechanical stresses have been shown to play a significant role in propagating a crack through the thickness of a membrane [1], although there is also a synergistic acceleration of the degradation from the chemical stressors [2]. To understand this degradation, it is critical to thoroughly investigate the mechanical behaviors of the membrane under in-situ cyclic conditions, so that alleviating strategies focusing on the fuel cell operating conditions can be developed.
In this work, we have interfaced a two-dimensional transient fuel cell transport/performance model (Grulke model) in Comsol [3] with a viscoelastic-plastic membrane mechanical model developed at the University of Delaware [4]. The modeling domain used for these two models is shown in Fig. 1. The Grulke model has been used to produce the spatiotemporal profiles of membrane water content in an operating cell which are then sent to the membrane mechanical model for calculating the mechanical parameters of interest. The Grulke model has comprehensive consideration of species transport and reaction kinetics in a fuel cell. Leveraging such strength leads to enhanced capability and fidelity in predicting the in-situ water distribution, and therefore the stress and strain, in the membrane. Using the combined model, we have studied the impacts of dynamically cycling hydration, current and voltage on a membrane.
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, B. Pence, and T. Ersal, “A 2D through-the-membrane transient model for polymer electrolyte membrane fuel cells”, 232nd ECS meeting, National Harbor, MD, 2017.
[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).