title: Tunable Mixed Ionic/Electronic Conductivity and Permittivity of Graphene Oxide Paper for Electrochemical Energy Conversion.
abstract: Graphene oxide (GO) is a two-dimensional graphitic carbon material functionalized with oxygen-containing surface functional groups. The material is of interest in energy conversion, sensing, chemical processing, gas barrier, and electronics applications. Multilayer GO paper has recently been applied as a new proton conducting membrane in low temperature fuel cells. However, a detailed understanding of the electrical/dielectric properties, including separation of the ionic vs electronic contributions under relevant operating conditions, has so far been lacking. Here, the electrical conductivity and dielectric permittivity of GO paper are investigated in situ from 30 to 120 °C, and from 0 to 100% relative humidity (RH) using impedance spectroscopy. These are related to the water content, measured by thermogravimetric analysis. With the aid of electron blocking measurements, GO is demonstrated to be a mixed electronic-protonic conductor, and the ion transference number is derived for the first time. For RH > 40%, conductivity is dominated by proton transport (with a maximum of 0.5 mS/cm at 90 °C and 100% RH). For RH < 40%, electronic conductivity dominates (with a maximum of 7.4 mS/cm at ∼80 °C and 0% RH). The relative permittivity of GO paper increases with decreasing humidity, from ∼10 at 100% RH to several 1000 at 10% RH. These results underline the potential of GO for application not only as a proton conducting electrolyte but also as a mixed conducting electrode material under appropriate conditions. Such materials are highly applicable in electrochemical energy conversion and storage devices such as fuel cells and electrolyzers.
authors.affiliation: International Institute for Carbon-Neutral Energy Research, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Faculty of Engineering, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bayer
authors.affiliation: International Institute for Carbon-Neutral Energy Research, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Bishop
authors.affiliation: International Institute for Carbon-Neutral Energy Research, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Nicola H
authors.initials: NH
authors.lastname: Perry
authors.affiliation: International Institute for Carbon-Neutral Energy Research, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Faculty of Engineering, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|Next-Generation Fuel Cell Research Center (NEXT-FC), Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|International Research Center for Hydrogen Energy, Kyushu University , Nishi-ku, Fukuoka, 819-0395, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Sasaki
authors.affiliation: International Institute for Carbon-Neutral Energy Research, Kyushu University , Nishi-ku, Fukuoka 819-0395, Japan.|School of Chemical and Process Engineering, University of Leeds , Leeds LS2 9JT, United Kingdom.|Department of Mechanical Engineering, University of Sheffield , Sheffield S10 2TN, United Kingdom.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Lyth
keywords: blocking layer measurement; graphene oxide; impedance spectroscopy; mixed conductivity; permittivity