title: Communication: nanoscale ion fluctuations in Nafion polymer electrolyte.
abstract: Ion conduction mechanisms and the nanostructure of ion conduction networks remain poorly understood in polymer electrolytes which are used as proton-exchange-membranes (PEM) in fuel cell applications. Here we study nanoscale surface-potential fluctuations produced by Brownian ion dynamics in thin films of low-hydration Nafion™, the prototype PEM. Images and power spectra of the fluctuations are used to derive the local conductivity-relaxation spectrum, in order to compare with bulk behavior and hopping-conductivity models. Conductivity relaxation-times ranged from hours to milliseconds, depending on hydration and temperature, demonstrating that the observed fluctuations are produced by water-facilitated hydrogen-ion hopping within the ion-channel network. Due to the small number of ions probed, non-Gaussian statistics of the fluctuations can be used to constrain ion conduction parameters and mechanisms.
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Brant
authors.initials: B
authors.lastname: Rumberger
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Mackenzie
authors.initials: M
authors.lastname: Bennett
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: Jingyun
authors.initials: J
authors.lastname: Zhang
authors.affiliation: National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, Maryland 20899, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Dura
authors.affiliation: Department of Physics, Northeastern University, Boston, Massachusetts 02115, USA.
authors.forename: N E
authors.initials: NE
authors.lastname: Israeloff