The nanopores of an as-synthesized cross-linked, cationic, type I bicontinuous cubic (QI)-phase lyotropic liquid crystal network were modified by exchange of its Br– counteranions in the pores with polymerizable 3-sulfopropyl acrylate anions, which were subsequently photopolymerized in situ. The formed anionic poly­(3-sulfopropyl acrylate) chains remain inside the pores even when the material is exposed to 1 M aq. salt solutions. After anionic polymer formation inside the pores, the QI network loses its overall ion exchange capacity, presumably because of complexation of the cationic matrix with the resident anionic polymer, and exhibits higher KCl sorption. However, the pore environment remains ionic, as confirmed by water and salt sorption measurements. Single-salt diffusion dialysis studies on supported QI thin film membranes containing the anionic polymer in the QI pores show that KCl permeates >70 and >150 times faster than K2SO4 at 0.05 and 0.5 M feed concentrations, respectively. In contrast, KCl permeates at the same or slower rate than K2SO4 through as-synthesized supported QI thin film membranes. The poly­(3-sulfopropyl acrylate) formed inside the QI pores is likely responsible for these observed ion sorption and transport differences.

Anion-exchange membranes (AEMs) often dehydrate and lose ionic conductivity in ferric chloride solutions used in all-iron or iron−chromium redox flow batteries (RFB). In this work, the change in material and ionic transport properties of three AEMs with similar concentrations of ion exchange sites and hydration numbers (mol H 2 O/mol ion exchange site) upon exposure to ferric chloride/ hydrochloric acid solutions were studied. Raman spectroscopy and iron sorption measurements show that FeCl 4 − occupies a fraction of the AEM ion exchange sites that depends on the ferric chloride concentration in the external solution. The AEM hydration number is linearly proportional to the amount of iron sorbed in the AEMs, suggesting that the displacement of the original hydrated Cl − counterions for unhydrated FeCl 4 − is the dominant mechanism for membrane dehydration. The ionic resistivity of the AEMs containing FeCl 4 − increased by as much as 4 orders of magnitude due to dehydration and, at high FeCl 3 solution concentrations (≥1.4M), also due to nonideal solution effects. Although the three AEMs have similar ion exchange site concentrations, the AEM with the closer local spacing of ion exchange sites exhibits higher FeCl 4 − sorption, and a correspondingly greater dehydration and resistivity increase in dilute FeCl 3 solutions.

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