Swelling and permeability of Nafion®117 in water–methanol solutions: An experimental and modelling investigation

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On the origin of the membrane potential arising across densely charged ion exchange membranes : How well does the teorell-meyer-sievers theory work?

A difference in salt concentration in two solutions separated by a membrane leads to an electrical potential difference across the membrane, also without applied current. A literature study is presented on proposed theories for the origin of this membrane potential (Φm). The most well-known theoretical description is Teorell-Meyer-Sievers (TMS) theory, which we analyze and extend. Experimental data for Φm were obtained using a cation exchange membrane (CMX, Neosepta) and NaCl solutions (salt concentration from 1 mM to 5 M). Deviations between theory and experiments are observed, especially at larger salt concentration differences across the membrane. At a certain salt concentration ratio, a maximum in Φm is found, not predicted by the TMS theory. Before the maximum, TMS theory can be used as a good estimate of ?m though it overestimates the actual value. To improve the theory, various corrections to TMS theory were considered: A) Using ion activities instead of ionic concentration in the external solutions leads to an improved prediction; B) Inhomogeneous distribution of the membrane fixed charge has no effect on Φm; C) Consideration of stagnant diffusion layers on each side of the membrane can have a large effect on Φm; D) Reducing the average value of the fixed membrane charge density can also largely affect ?m; E) Allowing for water transport in the theory has a small effect; F) Considering differences in ionic mobility between co-ions and counterions in the membrane affects Φm significantly. Modifications C) and F) may help to explain the observed maximum in Φm.</p

Mitigation of membrane scaling in electrodialysis by electroconvection enhancement, pH adjustment and pulsed electric field application

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Physicochemical and electrochemical characterization of Nafion-type membranes with embedded silica nanoparticles: Effect of functionalization

International audienceIntroduction of nanoparticles in membranes allows a significant enhancement of their performance in energy production, water treatment and other applications. However, the effect of nanoparticles’ surface functionalization and the mechanism of their impact on membrane properties remain poorly studied. In this paper, we examine a Nafion-based membrane and its modifications, each containing 3 wt% SiO2. The effect of functionalization by propyl, 3-aminopropyl and 3,3,3-trifluoropropyl is investigated. The water uptake, contact angle, conductivity, diffusion permeability to NaCl, current-voltage curves (CVC), chronopotentiograms (ChP), and the difference between the pH of the desalination compartment output and input solutions (characterizing the water splitting rate) are reported. It is found that the doping of the membranes with nanoparticles leads to increasing their conductivity in all cases except 3-aminopropyl, which imparts a positive charge to the nanoparticles; the diffusion permeability decreases and permselectivity increases in all cases. The latter is explained by transformation of the mesoporous membrane structure to the microporous one. The impact of nanoparticles on the membrane conductivity, CVC and ChP is mainly caused by an additional (positive) space charge introduced into the pore solution and at the membrane surface by the electric double layer surrounding the nanoparticles. The greater the surface charge density of the nanoparticles and the smaller their size, the stronger the impact. Accordingly, the highest conductivity, current density at a low fixed voltage and chronopotentiometric transition time are shown by the sample doped with SiO2 and 3,3,3-trifluoropropyl. The interplay between electroconvection and water splitting phenomena is discusse

Coupled transport phenomena in overlimiting current electrodialysis

The long-term goals of this work is to develop a better understanding of the coupled transport phenomena role in enhancement of salt ions transfer at electrodialysis of moderate-dilute and dilute electrolyte solutions in membrane modules of various constructions. Dependences of partial salt ions and H+(OH¿) fluxes through an anion-exchange membrane as a function of voltage applied to a membrane or a membrane channel were measured. On the base of the data obtained, reasons of the growth of salt ions `overlimiting' mass transfer in electrodialysis desalination channels with intermembrane distance and different NaCl solution concentration were analysed. It is shown that the role of gravitational convection may be important in desalination channels with a quite great intermembrane distance and electrolyte solution concentration. In this case a salt ions concentration at a membrane¿solution interface does not decrease to values sufficient for promoting the H+ and OH¿ generation and electroconvection. In desalination channels with small intermembrane distances, when treating dilute solutions, the salt concentration at the membrane surface reaches very small values. It promotes the H+ and OH¿ generation and a space charge region arising. An additional salt ions transfer occurs due to the exaltation effect as well as to the electroconvection. In this case the gravitational convection contribution is negligible

Competition between diffusion and electroconvection at an ion-selective surface in intensive current regimes

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