Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 56: Symposium: The Solid-Liquid Interface: A Challenge for Theoreticians I

O 56.5: Hauptvortrag

Donnerstag, 29. März 2007, 18:00–18:30, H36

Proton Conductors for Fuel Cells: The Role of Interfacial Structure and Dynamics — •Michael Eikerling, Ata Roudgar, and Sudha Narasimachary — Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada

Polymer electrolyte membranes (PEM) are the key components in polymer electrolyte fuel cells. Our work focuses on mechanisms of proton transport in the interfacial region between polymer fibrils and aqueous pathways in PEM. Understanding structure and dynamics at these ion-lined interfaces is of fundamental interest and it could facilitate the rational design of advanced PEM. As a basic model for performing ab-initio quantum mechanical calculations we consider a dense 2D array of ionized surface groups under conditions of minimal hydration. In optimization studies we found a critical separation 7Å of surface groups for the transition between highly ordered and clustered interfacial conformations. The transition from weak to strong binding of additional water molecules occurs also at 7Å. We systematically explore effects of density and chemical architecture of surface groups on conformations, strength of water binding, and interfacial dynamics. Our calculations have identified tilting of surface groups, rotation of acid head groups, and lateral shift of hydronium ions as relevant collective coordinates that control proton motion at the hydrated interface. Currently, we utilize ab-initio molecular dynamics and transition path sampling methods to systematically study free energy profiles along reaction paths and determine relevant transition rates.