Co-ion Effects in Fuel Cell Membranes

Abstract

Anion exchange membrane fuel cells have received particular attention in recent years because they can overcome the problems of electrolyte leakage and carbonate precipitation in traditional alkaline fuel cells. Often, because perfect ion exchange in syntheses of fuel cell membranes is not possible, multiple ions can coexist in the membranes. Such co-ionic systems have non-trivial transport properties due to the competition between ions. In this presentation, I will talk about an anion exchange membrane with different ratios of fluoride and chloride ions. At 300 K, our molecular dynamics simulation results showed that the self-diffusion constant of fluoride increases by about 70% when fluoride content decreases from 100% to 40% (and 60% Cl), and it increases by about 140% when fluoride content decreases from 100% to 10%. We provide evidence that the enhancement in fluoride mobility is due to the larger size of the chloride ion, which more readily loses its water solvation shells because of a lower surface electric field. This in turn frees up more water for ion transport. I will also show such co-ion effects are more general than just the fluoride/chloride case.


References

1. Tse, Y.-L. S.; Voth, G. A.; Witten, T. A., Ion Mixing, Hydration, and Transport in Aqueous Ionic Systems. J. Chem. Phys. 2015, 142 (18), 184905.

2. Tse, Y.-L. S.; Sarode, H. N.; Lindberg, G. E.; Witten, T. A.; Yang, Y.; Herring, A. M.; Voth, G. A., Chloride Enhances Fluoride Mobility in Anion Exchange Membrane/Polycationic Systems. J. Phys. Chem. C 2014, 118 (2), 845-853.


Biography

Steve Tse received his PhD in theoretical chemistry under the guidance of Prof. Hans C. Andersen at Stanford University in 2011. During his PhD work, he focused on developing new theories and simulation tools, using statistical mechanics, for studying microscopic molecular motion in stochastic models of liquids with highly cooperative dynamics. After PhD, as a Croucher Fellow at the University of Chicago, he began his postdoctoral work with Prof. Gregory Voth and Prof. Thomas Witten to study the charge transport in both aqueous solutions as well as fuel cell membranes by molecular dynamics simulations. In particular, he developed new reactive multiscale models to understand proton/hydroxide transport. In 2015 Oct, he joined the Chinese University of Hong Kong (CUHK) as Assistant Professor. Since the start of Tse research group at CUHK Chemistry Department, his team has been studying different interfacial systems including air-water and fluid-fluid/solid interfaces. A major theme of the research has been to understand the thermodynamics and the dynamics of these systems and the relationships between the two. Recently, he has started a collaboration to understand the chemical kinetics and thermodynamics of asymmetric organic reactions. He has been recently promoted as Associate Professor.