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).

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.

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.

In this paper, a commercial polymeric resin precursor (polystyrene sulphonate beads) was used as a source of carbon spheres. The resin was pyrolyzed at different temperatures (700, 800, and 900 °C) and the resulting carbons were analyzed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). From the result of EIS, carbon spheres obtained at 700 °C (CS−700) have the least ohmnic resistance and highest capacitance. In furtherance, the resin was chemically activated with iron (III) chloride FeCl₃·6H₂O at different concentration (0.1 M, 0.3 M, and 0.5 M) and pyrolyzed at 700 °C to obtain activated carbon sphere namely (ACS 700−0.1, ACS 700−0.3, and ACS 700−0.5) in which the last digit of the samples denotes the concentration of FeCl₃. Scanning electron microscope (SEM) showed that the carbon is of spherical shape; X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and X-ray photon electron spectroscopy (XPS) revealed successful introduction of Fe on the surface of the carbon. Out of all the activated carbon spheres, ACS 700−0.1 exhibited highest double layer capacitance of 9 µF cm⁻² and lowest charge transfer resistance of 3.33 KΩ·cm². This method shows that carbon spheres obtained from a polymeric source can be easily improved by simple resin modification and the carbon could be a potential candidate for an electrical double layer capacitor.

Mise en place, évaluation et optimisation de la désionisation capacitive en flux: A purification de l'eau consiste à transformer une eau non potable en une eau suffisamment bonne pour être consommée et utilisée par l'homme. La déionisation capacitive est une nouvelle technique prometteuse de dessalement de l'eau, proche des technologies de dessalement établies telles que l'osmose inverse (RO), etc. Elle fonctionne à basse pression et peut potentiellement utiliser moins d'énergie pour le dessalement de l'eau saumâtre.Dans une cellule CDI typique, l'eau d'alimentation traverse la couche séparatrice entre deux électrodes de carbone chargées électriquement. Cette architecture entraîne d'importantes limitations de performance car les électrodes sont à l'état solide avec une surface de contact exposée et des pores pour l'adsorption limités. De plus, il est impossible d'offrir un mode de fonctionnement continu.Nous décrivons ici une architecture alternative, où l'électrode d'alimentation est à l'état liquide et s'écoule de manière semi-continue sur des canaux sculptés. En utilisant cette technique, nous montrons que la déionisation capacitive à flux permet de réduire de manière significative le temps de dessalement et peut dessaler une solution d'alimentation plus élevée. Nous démontrons ces avantages en utilisant du charbon actif en poudre du commerce et du charbon actif superficiel comme matériaux d'électrode. Le charbon superficiel à une charge de carbone modérée rivalise avec les performances du charbon actif en poudre en raison de sa taille de particule réduite. En outre, les propriétés physico-chimiques et électrochimiques des électrodes solides et fluides (électrodes vierges et modifiées) ont été caractérisées par des mesures d'adsorption d'azote à basse température, le microscope électronique à balayage (MEB), la diffraction des rayons X (DRX), la spectroscopie Raman, la spectroscopie photoélectronique à rayons X (XPS), l'infrarouge à transformée de Fourier (FT-IR), la voltampérométrie cyclique (CV) et la spectroscopie d'impédance électrochimique (SIE).Nous présentons également une stratégie de réduction de la polarisation de concentration des électrodes à base de carbone par l'utilisation de nanofibres synthétisées par la méthode d'électrofilage et, en conséquence, une amélioration notable a été apportée par des approches expérimentales par spectroscopie d'impédance électrochimique et des études de voltampérométrie cyclique des électrodes de carbone nanocomposites hybrides. En outre, nous démontrons que nos approches sont prometteuses pour l'optimisation des électrodes CDI/FCDI et pour la résolution de certains problèmes inhérents aux électrodes à base de carbone.