title: Direct determination of ionic transference numbers in ionic liquids by electrophoretic NMR.
abstract: Charge transport in ionic liquids is a phenomenon of utmost interest for electrochemical (e.g. battery) applications, but also of high complexity, involving transport of ion pairs, charged clusters and single ions. Molecular understanding is limited due to unknown contributions of cations, anions and clusters to the conductivity. Here, we perform electrophoretic NMR to determine electrophoretic mobilities of cations and anions in seven different ionic liquids. For the first time, mobilities in the range down to 10(-10) m(2) V(-1) s(-1) are determined. The ionic transference number, i.e. the fractional contribution of an ionic species to overall conductivity, strongly depends on cation and anion structure and its values show that structurally very similar ionic liquids can have cation- or anion-dominated conductivity. Transference numbers of cations, for example, vary from 40% to 58%. The results further prove the relevance of asymmetric clusters like [CationXAnionY](X-Y), X ≠ Y, for charge transport in ionic liquids.
authors.affiliation: Institute of Physical Chemistry, University of Muenster, Corrensstraße 28/30, 48419 Münster, Germany. schoenho@uni-muenster.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Gouverneur
authors.affiliation: Institute of Physical Chemistry, University of Muenster, Corrensstraße 28/30, 48419 Münster, Germany. schoenho@uni-muenster.de.
authors.forename: Jakob
authors.initials: J
authors.lastname: Kopp
authors.affiliation: Institute of Physics, Augsburg University, Universitätsstraße 1, 86159 Augsburg, Germany.
authors.forename: Leo
authors.initials: L
authors.lastname: van Wüllen
authors.affiliation: Institute of Physical Chemistry, University of Muenster, Corrensstraße 28/30, 48419 Münster, Germany. schoenho@uni-muenster.de.
authors.forename: Monika
authors.initials: M
authors.lastname: Schönhoff