Modeling of conductive transport in proton-exchange membranes for fuel cells

An adequate understanding of the conductivity of polyperfluorosulfonic acid (PFSA) membranes as a function of water content, or relative humidity, and temperature is necessary for an analysis of the functioning of proton-exch ange membrane (PEM) fuel cells. Although much work has been done toward elu cidating the microstructure and conduction mechanism in PFSA, a satisfactor y theoretical model with a minimum of fitted parameters is not yet availabl e. Such a model is developed here for the conduction of protons in hydrated Nafion(R) or like membranes based on the dusty-fluid model for transport a nd the percolation model for structural aspects. Further, thermodynamics of dissociation of the acid groups in the presence of polar solvents such as water is included. The sorption of solvent from vapor is modeled using a fi nite-layer Brunauer-Emmett-Teller (BET) model. With the only fitted paramet ers employed being the BET constants, determined independently, and the rat io of diffusion coefficients representing the interaction of the protonated solvent molecules with solvent and that with the membrane, the model provi des excellent correlation with a variety of experimental data. (C) 2000 The Electrochemical Society. S0013-4651(00)01-112-5. All rights reserved.