Key factor governing transient maldistribution in proton exchange membrane fuel cells: A numerical study on decoupling modeling framework and sorption rate asymmetry

Abstract

Accurate transient modeling of proton exchange membrane fuel cells (PEMFCs) requires careful treatment of ionomer water sorption and desorption kinetics. To address uncertainties in modeling approaches, this study utilizes a transient, three-dimensional, two-phase, non-isothermal model under 50% relative humidity conditions. We first compared widely used representative sorption-rate models, which differ in modeling frameworks (equation-based vs. constant-rate) and sorption-rate coefficient symmetry (symmetric vs. asymmetric). Their intertwined characteristics were then systematically decoupled to assess the isolated effect of each factor on transient dynamics. Within the load-step protocols and operating conditions investigated in this study, the modeling framework has a secondary influence on predicted transient behaviors and spatial distributions, as a constant-rate model with matched time-averaged coefficients captures the main trends of the equation-based results. In contrast, sorption-rate coefficient symmetry plays a decisive role. Desorption-dominant asymmetry in the sorption-rate coefficients causes severe local dehydration and a redistribution of current density during galvanostatic transients. Among water phases, the ionomer water content shows the greatest sensitivity to the sorption-rate model, with the most direct link to the current density distribution. This 3D analysis provides guidance for future modeling by showing how sorption-rate model selection and coefficient parameterization influence the prediction of transient performance and spatial nonuniformity, which are not observable in lower-dimensional models.