Understanding the Mechanism of Ionic Conductivity in an Anhydrous Proton-Conducting Electrolyte Through Measurements of Single-Ion Diffusion Coefficients

Abstract

The single-ion diffusion coefficients of and ions have been electrochemically measured in a series of anhydrous proton-conducting electrolytes composed of mixtures of acid (where , 7, 12, or 16) dissolved in our polymer. The electrochemically measured single-ion diffusion coefficients in this electrolyte are dependent on temperature such that, at low temperatures , the cation is the primary charge carrier in the four acid/polymer solutions tested. However at high temperatures, the diffusion coefficients of the and anions are larger than the corresponding diffusion values, yielding a smaller fraction of charge carried by ( values of 0.29 and 0.41, for the and mixtures at ). While the diffusion coefficient of the large anion does not overtake at , its transference number nonetheless increases with increasing temperature. We conclude that our electrolyte is dominated by Grotthus conductivity at low to moderate temperatures, while the contribution of the vehicle mechanism of conductivity increases at high temperatures.