Non-Linear First-Harmonic Impedance in Ion-Exchange Membrane Systems under Potentiostatic Control in the Limiting Current Regime

International audienceThe harmonic response of ion-exchange membrane systems under potentiostatic control in the limiting current regime is studied. The transport of an electroneutral binary electrolyte through a cation-exchange membrane and the two diffusion boundary layers adjacent to the membrane is described by means of a Nernst-Planck analysis. The full system is perturbed with a sine voltage of a single frequency superimposed on a direct voltage, and it is obtained the decomposition in a Fourier series of the resulting electric current using the network simulation method. The effect of the different parameters characterizing the perturbing voltage (amplitude, frequency and dc component) on the second harmonic of the resulting current, and their influence on the first-harmonic impedance in a highly biased ion-exchange membrane system, are analyzed and discussed. The behavior of the resistance associated to the first harmonic impedance at the limit of zero frequency has been particularly analyzed and an analytical expression to roughly estimate its dependence on the voltage amplitude has been derived. Auxiliary methods for linearity assessment such as Kramers-Kronig transforms, Lissajous plots and waveforms are also discussed

Flow electrode capacitive deionization for water desalination: optimizing ion removal capacity and flowing properties of activated carbon suspensions

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Towards Electrochemical Water Desalination Techniques: A Review on Capacitive Deionization, Membrane Capacitive Deionization and Flow Capacitive Deionization

Electrochemical water desalination has been a major research area since the 1960s with the development of capacitive deionization technique. For the latter, its modus operandi lies in temporary salt ion adsorption when a simple potential difference (1.0–1.4 V) of about 1.2 V is supplied to the system to temporarily create an electric field that drives the ions to their different polarized poles and subsequently desorb these solvated ions when potential is switched off. Capacitive deionization targets/extracts the solutes instead of the solvent and thus consumes less energy and is highly effective for brackish water. This paper reviews Capacitive Deionization (mechanism of operation, sustainability, optimization processes, and shortcomings) with extension to its counterparts (Membrane Capacitive Deionization and Flow Capacitive Deionization)

Assess of physical antiscale-treatments on conventional electrodialysis pilot unit during brackish water desalination

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Current status of surface water in the Mekong Delta, Vietnam: Threats for drinking water supply and treatment technologies

International audienc

"Ion exchange membraes and associated processes. A state of the art and new trends"

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Comparative Investigation of Activated Carbon Electrode and a Novel Activated Carbon/Graphene Oxide Composite Electrode for an Enhanced Capacitive Deionization

Capacitive deionization is an emerging brackish water desalination technology whose principle lies in the utilization of porous electrodes (activated carbon materials) to temporarily store ions. Improving the properties of carbon material used as electrodes have been the focus of recent research, as this is beneficial for overall efficiency of this technology. Herein, we have synthesized a composite of activated carbon/graphene oxide electrodes by using a simple blending process in order to improve the hydrophilic property of activated carbon. Graphene oxide (GO) of different weight ratios was blended with commercial Activated carbon (AC) and out of all the composites, AC/GO-15 (15 wt.% of GO) exhibited the best electrochemical and salt adsorption performance in all operating conditions. The as prepared AC and AC/GO-x (x = 5, 10, 15 and 20 wt.% of GO) were characterized by cyclic voltammetry and their physical properties were also studied. The salt adsorption capacity (SAC) of AC/GO-15 at an operating window of 1.0 V is 5.70 mg/g with an average salt adsorption rate (ASAR) of 0.34 mg/g/min at a 400 mg/L salt initial concentration and has a capacitance of 75 F/g in comparison to AC with 3.74 mg/g of SAC, ASAR of 0.23 mg/g/min and a capacitance of 56 F/g at the same condition. This approach could pave a new way to produce a highly hydrophilic carbon based electrode material in CDI

Activated Carbon Blended with Reduced Graphene Oxide Nanoflakes for Capacitive Deionization

Capacitive deionization is a second-generation water desalination technology in which porous electrodes (activated carbon materials) are used to temporarily store ions. In this technology, porous carbon used as electrodes have inherent limitations, such as low electrical conductivity, low capacitance, etc., and, as such, optimization of electrode materials by rational design to obtain hybrid electrodes is key towards improvement in desalination performance. In this work, different compositions of mixture of reduced graphene oxide (RGO) and activated carbon (from 5 to 20 wt% RGO) have been prepared and tested as electrodes for brackish water desalination. The physico-chemical and electrochemical properties of the activated carbon (AC), reduced graphene oxide (RGO), and as-prepared electrodes (AC/RGO-x) were characterized by low-temperature nitrogen adsorption measurement, scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red (FT-IR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Among all the composite electrodes, AC/RGO-5 (RGO at 5 wt%) possessed the highest specific capacitance (74 F g−1) and the highest maximum salt adsorption capacity (mSAC) of 8.10 mg g−1 at an operating voltage ∆E = 1.4 V. This shows that this simple approach could offer a potential way of fabricating electrodes of accentuated carbon network of an improved electronic conductivity that’s much coveted in CDI technology

Noise Analysis of Ion Transport Through Charged Membranes

International audienc