(576e) Nanoscale Membrane Design Principles for Optimizing Proton Conductivity

A model for charge transport in aqueous systems is used to provide insights into design of proton exchange membranes that optimize charge transport.  The model accounts for the effect of acidity, confinement and connectivity on the diffusivity and has been shown to quantitatively agree with experimental measurements of charge self-diffusivity in Nafion [Esai Selvan, M., et al.  J. Phys. Chem. B 115 2011 pp 3052–3061] and in cross-linked and sulfonated polycyclohexadiene.  In this presentation, the origin of the theoretical model is described.  The model is applied to water-filled cylindrical nanopores functionalized on their interior surface with acid groups.  It is demonstrated that for cylindrical nanopores of a given radius there is an optimal surface coverage of acid groups.  The optimum can be sharply peaked, indicating that non-optimal surface coverages (either too low or too high) drastically reduce the conductivity of the pore.  The theoretical maximum conductivity through a cylindrical nanopore is calculated to be about 0.70 S/cm at 300 K.  Comparison with available experimental results is made.  Limitations of the model are also discussed.