(589b) Molecular-Level Modeling of the Structure and Wetting of Electrode/electrolyte Interfaces

We have used Molecular Dynamics (MD) simulations to investigate the structural and dynamical properties of the electrode/electrolyte interface in hydrogen Proton Exchange Membrane (PEM) fuel cells. Specifically, we have studied the hydrated Nafion membrane, humidified in a range from 5% to 20% water by weight. We have examined three interfacial systems that include this polyelectrolyte: (1) the membrane/vapor interface, (2) the membrane/vapor/catalyst surface interface, and (3) the membrane/vapor/catalyst support surface interface. In these simulations, the vapor phase is water, the catalyst phase is platinum and the support phase is graphite. These molecular simulations represent portions of interfaces that exist within the PEM fuel cell. We compare the structural and dynamical properties of the bulk hydrated membrane with those present in the three interfacial systems. We examine the transient equilibrium wetting of the two solid surfaces. We see significant wetting of the Pt surface and virtually no wetting of the graphite phase. Finally, we examine a fourth interfacial system in which the Pt surface is separated from the membrane interface by a gap of graphite surface. We examine the potential for proton transport across this gap, as a function of gap size. Finally, we connect the results of the molecular-level simulations with the overall macroscopic transport of protons across the electrode/electrolyte interface.

Acknowledgments The work is supported by a grant from the U. S. Department of Energy BES under the contract number DE-FG02-05ER15723. This research used resources of the Center for Computational Sciences at Oak Ridge National Laboratory, which is supported by the Office of Science of the DOE under Contract DE-AC05-00OR22725.