Electrochemical impedance spectroscopy of enhanced layered nanocomposite ion exchange membranes

Abstract

This work presents the enhancement of Cl − /SO 4 2 − mono-selectivityof layered nanocomposite anion exchange membranes (AEMs) and the mechanism that supportsthis improvement. These nanocomposite membranes are based on commercial polyethylene AEMs and a nanocomposite negative thin layer composed of sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) and a functionalized nanomaterial, Fe 2 O 3 −SO 4 2− nanoparticles or oxidized multi-walled carbon nanotubes CNTs-COO −. The mechanism for monovalent selectivity was confirmed by characterizing nanocomposite membranes and commercial heterogeneous ion exchange membranes (IEMs) using ζ-potential and electrochemical impedance spectroscopy (EIS). ζpotential measurements confirmed the modification of the charge of surface of the membrane after being coated with the nanocomposite layer. EIS measurements showed a totally different Highlights  EIS was applied to tailor-made layered nanocomposite membranes  An equivalent electric circuit based on the Maxwell-Wagner model was applied  The equivalent electric circuit is related to the structure of the layered membranes  Differences in dielectric constant in the layered membrane influence depletion layers  Layered nanocomposite membrane stability can be easily assessed by EIS

Ionic Mobility in Ion-Exchange Membranes

“…This shows the importance of investigation of ionic and molecular mobility in ion-exchange membranes [ 60 , 64 ]. Impedance spectroscopy is undoubtedly the main method for studying ionic mobility in solids [ 65 , 66 , 67 , 68 ], but it usually provides information on the total conductivity. Blocking electrodes can be used to separate the contributions of different ions [ 69 ], although this significantly complicates the measurement procedure.…”

Characterization of Poly(Acrylic) Acid-Modified Heterogenous Anion Exchange Membranes with Improved Monovalent Permselectivity for RED

“…In this context, surface modification of AEMs represents one of the most promising strategies to render a monovalent permselectivity as well as increasing fouling resistance [19][20][21]. Although different modification techniques such as polymerization by UV-irradiation [22] or chemical oxidation [23], among others, have been addressed in literature in an attempt to overcome the so-mentioned limitations, the possibility of incorporating a negative hydrophilic layer (or multilayers) on an AEM surface represents an attractive option for the electro-membrane processes field [24], because such a layer would act not only as a multivalent ions rejection wall, but also favoring monovalent ions passage owing to the Donnan effect [17,25], and preventing fouling because of its hydrophilic properties and negative charge at the same time [26].…”

Advanced Materials for Polymeric Ultrafiltration Membranes Fabrication and Modification

“…Vaselbehagh et al (2014; reported that the antifouling potential and the monovalent anion selectivity were improved by the surface modification with polydopamine. Fernandez-Gonzalez et al (2017a; also reported that these properties were improved by the surface modification with carbon nanotubes or sulfonated iron oxide nanoparticles. Thus, it is clear that the antifouling property and the monovalent anion selectivity are improved simultaneously by the surface modification of AEM.…”