Kinetic and transport modeling in proton exchange membrane fuel cells

Abstract

The improvement of PEMFC performance and durability requires a quantitative understanding of the processes that cause performance losses. In this dissertation, two models are developed incorporating new processes that have been poorly described or neglected in previous literature sources (catalyst oxide layer, hardware effects, enhanced vapor diffusion, and interfacial saturation). In simulations of electrochemical impedance spectroscopy (EIS), the kinetic effect of the catalyst oxide layer is found to cause a large, low-frequency inductive loop in agreement with experiments. Accounting for the inductive loop unifies steady-state measurements of resistance with EIS measurements, solving a long-standing barrier to accurate interpretation of EIS. Furthermore, flooding losses due to two-phase water transport are one of the most poorly understood losses and are a major area for improvement. The addition of an interfacial saturation effect is found to provide the best explanation of flooding. Heat transfer is shown to be the controlling factor in the performance of PEMFCs under certain flooded conditions. The advancements of this dissertation in the modeling of the oxide layer and two-phase transport phenomena represent significant steps towards the goals of EIS analysis by physics-based model and a mathematical understanding of performance degradation due to carbon corrosion and flooding.