(702d) Molecular Dynamic Simulations of the Effect On the Hydration of Nafion at the Presence of Nanoparticle | AIChE

(702d) Molecular Dynamic Simulations of the Effect On the Hydration of Nafion at the Presence of Nanoparticle


Zhang, S. - Presenter, University of Tennessee
Keffer, D. J. - Presenter, University of Tennessee, Knoxville
Adhangale, P. - Presenter, University of Tennessee

Nafion possesses good chemical, thermal and mechanical properties as a proton conductive membrane in proton exchange membrane (PEM) fuel cells with relatively high proton conductivity.  As such, Nafion is the current industry standard PEM. Nafion performs best under the high humidity conditions at moderate temperature.  From the perspective of the catalyst in a fuel cell, one would like to increase the operating temperature of the fuel cell (1) to increase the activity of the catalyst, (2) decrease the susceptibility to catalyst poisoning by CO and (3) reduce the amount of catalyst required.  However the performance of Nafion falls rapidly as the temperature rises over 80 0C due to dehydration of the membrane, which results in a drastic drop in conductivity. 

Consequently, there has been a tremendous effort to develop membranes that retain moisture at higher temperatures (90-120 0C), with the understanding that better retention of water will result in higher conductivities in the PEM at elevated temperatures.  The investigation of new high temperature membranes include composite membranes in which Nafion contains an hydrophilic inorganic material either in the form of an interpenetrating nanostructured matrix or as dispersed nanoparticles.

Various materials such as SiO2, ZrO2, TiO2 and Pt have been evaluated over the past two decades for their ability to improve the performance of fuel cells at elevated temperatures. The results showed that the weight fraction of nanoparticle as well as the morphology, surface orientation and modification of the nanoparticles have important effects on the ability to retain moisture and on the resulting conductivities. These improved properties were reasoned to the strong interfacial interactions between the polymer matrix and the filler surface, as opposed to the conventional composites. However, a clear molecular-level understanding of such effects does not currently exist.

In this study, molecular dynamic simulations were applied to investigate the role of the various nanoparticles dispersed in Nafion polymers in the retention of moisture and promotion of high conductivities.  Simulations in the isobaric-isothermal ensemble are used to predict composite membrane densities and water content as a function of temperature and relative humidity.