(452e) Towards the Engineering of Electrolytes Through Multi-Scale Modeling and Simulation

Proton exchange membranes (PEMs) are the electrolyte in current state-of-the-art fuel cells and function as not only the separator of the electrodes and reactant gases (H₂ and O₂) but importantly as the internal ion conductor. Efficient operation of these energy conversion devices in diverse applications (vehicular, portable, and stationary) places demands on the PEM which include: long-time thermal and chemical stability (including resistance to oxidation and degradation by reactive species) at temperatures as high as 120°C, and high proton conductivity (≈ 10^-1 Scm^-1) under low humidity conditions (25-50% relative humidity). Although a large number of strategies have been devised in the pursuit of membranes that meet these requirements, current PEM fuel cells still utilize perfluorosulfonic acid (PFSA) ionomers such as Nafion®. Recently, proton conduction in these polymeric materials has been developed within a framework consisting of: complexity, connectivity, and cooperativity. Experiments and modeling have shown that the transport of water and hydrated protons within PFSAs is dependent upon: the characteristic dimensions of the phase-separated hydrated polymer morphology (typically on the order of only a few nanometers); acidity, density, and distribution of the sulfonic acid groups; and the external conditions including humidity, temperature, and pressure. A complete understanding of how all these factors may be used in a synergetic fashion in the engineering of novel high performance materials remains forth-coming. This talk will describe our multi-scale modeling effort in securing a fundamental molecular-level understanding of how structure determines function and properties.