Theoretical Interpretation of Ion Velocities in Concentrated Electrolytes Measured by Electrophoretic NMR

Author(s): Timachova, K; Newman, J; Balsara, NP | Abstract: © The Author(s) 2019. Published by ECS. Electrophoretic NMR (eNMR) is emerging as a powerful technique for characterizing ion transport in electrolyte systems. We show that the standard approach for analyzing eNMR data is valid only for dilute electrolytes and provide a theoretical framework for interpreting eNMR results for all binary electrolyte systems with univalent salts. We derive relationships between the velocities of the ion species and the solvent in terms of the electrochemical Stefan-Maxwell diffusion coefficients and provide modified expressions for correctly calculating the transference number and conductivity from eNMR data in concentrated electrolytes. Our approach suggests that it is necessary to measure not just the displacement of ion species during the application of current in an eNMR experiment but also the displacement of the uncharged solvent in order to correctly calculate ion mobilities and the transference number.