Model-Based Analysis of PFSA Membrane Mechanical Response to Relative Humidity and Load Cycling in PEM Fuel Cells

Abstract

The hydration/dehydration cycling of the membrane during the fuel cell operation and the resulting mechanical stress are in part responsible for the mechanical failures of a polymer electrolyte membrane. To thoroughly investigate the mechanical behaviors of the membrane under in-situ cyclic conditions, in this paper, we have interfaced a comprehensive two-dimensional transient fuel cell transport model with a viscoelastic-plastic membrane mechanical model. The transport model is used to produce the spatiotemporal profiles of membrane water content and temperature in an operating cell, which are then sent to the membrane mechanical model to calculate the mechanical parameters of interest. This provides the extended capability of studying the membrane mechanical response under in-situ conditions, which was not possible with the original mechanical model. The effects of cycling relative humidity and voltage and current at different temperatures on the membrane stresses are studied using the coupled model. It is found that the location of maximum in-plane tensile stress can vary significantly with the operating temperature during voltage cycling, whereas the highest in-plane compressive stress occurs under the land for all cases, particularly near the cathode. The simulation results confirm the need for coupling the two models to capture comprehensive transport phenomena in studying the membrane mechanical behaviors, and represent an important step toward improved understanding of various synergistic mechanical failure mechanisms that affect the membrane in an operating fuel cell.