(Keynote) Selective Transport of Ionic Species in Membranes - Effects of Specific Interactions and Nano-Morphology

Abstract

Selective transport of specific ions is not only key to certain chemical and electrochemical applications, it also raises a number of interesting fundamental questions. For example, in a redox-flow battery, a membrane has to efficiently separate the electrochemically active ionic species (e.g. the different vanadium species present in anolyte and catholyte of a VRFB) while conducting other ionic species for mediating the electrochemical reactions. Fundamentally, selective transport is related to issues of ion uptake and ion mobility. There may be preferred uptake of certain ionic species while others may dominate ionic transport; under certain conditions, an anion exchange membrane (AEM) may even turn into a proton conductor.This presentation provides insight into the effects membrane morphology and chemical interactions have on selective ion transport. Common thermodynamic considerations have been modified by including effects of ion solvation and the influence acid/base properties of the fixed ions have on counter-ion condensation. In addition, insights into the membrane’s nano-morphology allowed to identify sterical effects on ionic transport (ion-sieving).With these sophistications, transport data are described in a quantitative way and guidelines are provided which may help to select or tailor membranes for particular applications requiring selective ion transport.