Ion Transport through Ultrathin Electrolyte under Applied Voltages

Abstract

The influence of the Coulomb transport (CT) effect on ion transport in electrolytes is evaluated through two prototypical systems: the [IrCl 6 ] 2-/3- redox couple in aqueous solution and Mg 2+ (with TFSI - counterions) in acetonitrile solution. In the first system, transport of the [IrCl 6 ] 2-/3- anions is inhibited, and ions are trapped near the positive electrode due to the unscreened electric field. With larger applied voltage, the inhibition is stronger. This effect can be weakened, however, by adding supporting charges, which screen the electric field of the electrodes. In the second system, the unscreened electric field provides a means of separating [Mg x (TFSI) y ] (2x-y)+ clusters in the electrolyte. This effect enhances charge transport by providing a larger number of faster-moving (smaller) ions. Considered together, these systems provide examples of how the CT effect may increase or decrease charge transport and how one might attempt to modulate this effect in order to enhance electrochemical cell conduction.