Final Report

Taylor, Philip L.

关键词: Fuel cells;    Nafion;   

DOI  :  10.2172/1055769
RP-ID  :  DOE/ER46244-4
PID  :  OSTI ID: 1055769

学科分类：凝聚态物理

美国|英语

来源: SciTech Connect

【 摘 要 】

Our research program was aimed at elucidating the nature of proton transport in ionomer membranes by means of a combination of analytical theory and molecular modeling. There were two broad thrusts. The first of these was directed towards understanding the equilibrium structure of Nafion and related polymers at various levels of hydration. The second thrust was concerned with the transport of protons through a membrane of this type. The research on structure proceeded by building on existing work, but with the introduction of some novel techniques, among which is a hybrid Molecular Dynamics--Monte Carlo approach. This method permits rapid computations by temporarily decoupling the motion of the polar side chains from that of the perfluorinated backbone, while still retaining the essential aspects of the constraint that phase separation can only continue to a very limited degree. Competition between an elastic energy due to this constraint and the tendency to phase separation lead to the equilibrium structure, which turns out to be qualitatively different at different levels of hydration. The use of a carefully formulated dielectric function was necessary to achieve accurate results. The work on transport of protons in Nafion-like membranes also involved a combination of theory and simulation. Atomistic molecular-dynamics simulations were employed to determine some of the characteristic parameters for the diffusion of hydronium in hydrated membranes. These results were used in a theoretical model of non-linear diffusion to predict transport coefficients. Among our results was the discovery that treatment with strong electric fields may enhance the properties of the polymer membranes. Our computer simulations showed that the vigorous application of a stretching force or an electric field can modify the structure of the ionomer that lies at the heart of a polymer-electrolyte-membrane fuel cell. If these predictions are verified experimentally, then it should be possible to produce fuel cells capable of delivering much higher currents than those currently available.