(303e) Molecular Dynamics Simulations of Polymer Electrolyte Membrane Interfaces

Polymer electrolyte membranes are an important component of hydrogen fuel cells, and materials for these membranes are selected to maximize proton conductivity. Currently, the material of choice is Nafion, a polyperfluorosulfonic acid. The proton conductivity of Nafion is highly sensitive to the amount of water in the membrane because water molecules aggregate into nano-scale clusters that act as conduits for protons.¹ Consequently, water uptake and retention is a practical concern in fuel cell operation. Recent experiments suggest that the air/membrane interface constitutes a significant transport barrier to water uptake, while the liquid water/membrane interface is a much smaller barrier.²The molecular origin of these barriers is not well understood.

Atomistic molecular dynamics simulations of the air/membrane and liquid/membrane interfaces will be presented, revealing local concentrations and configurations of polymers chains that differ substantially from bulk behavior. Mass transfer resistances at these interfaces are directly calculated using a non-equilibrium molecular dynamics technique.

[1] Mauritz, K. A.; Moore, R. B. Chem. Rev. 2004, 104, 4535–4586.

[2] Majsztrik, P.; Bocarsly, A.; Benziger, J. J. Phys. Chem. B 2008, 112, 16280–16289.