The research presented in this thesis is a contribution to the modeling and understanding of the dynamic behavior of proton exchange membrane fuel cells (PEMFCs). A time-dependent, two-phase non-isothermal model of the membrane electrode assembly was developed and implemented using the finite element method. In addition to solving a phenomenological transport equation for water in the membrane, the model takes into consideration the non-equilibrium water sorption to better capture some of the dynamic characteristics of water transport in the MEA. Mass transfer using Fickian diffusion is implemented in the model. Two different models describing the electrochemical reactions in the catalyst layer including a macro-homogeneous model and an agglomerate model, are also implemented. Conservation of energy is included in the solution procedure in order to assess the impact of thermal effects on the dynamics of the transport in the MEA. For the purpose of model and concept validation, the model was first solved in a steady two-dimensional mode for a through- plane computational domain using a commercial software package, COMSOL Multiphysics version 3.2b. The impact of using a single- and two-phase modeling approaches was evaluated, and the predicted current-voltage performance characteristic are found in good agreement with the experimental data available in the literature. In addition, the developed model was benchmarked against a finite element-based in-house code for further validation and to evaluate numerical accuracy and computational performance.

Transient simulations of operation under dynamic voltage sweeps are presented, and parametric studies are conducted to investigate the impact of various model, operation and transport properties on the predicted dynamic cell performance. In particular, the rate of load change, the difference in water content between the anode and cathode, and the water sorptions rate are shown to have significant impact on cell performance in unsteady operation, especially at higher current densities. Parametric studies also address the sensitivity of the model results to physical properties, highlighting the importance of accurately determining certain physical properties of the fuel cell components. Finally, the application of the model to air-breathing fuel cells provides further insight into the dynamic performance characteristic of such type of fuel cells.