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In this Article, the consequence of continuous electrochemical oxidation at the positive electrode in an initially symmetrical capacitive deionization (CDI) cell, comprising two identical activated carbon electrodes, is examined and discussed. Extensive and intensive parameters of the CDI cell are defined, and the deviations occurring among them as a result of continuous electrochemical oxidation processes at the positive electrode during prolonged charge–discharge cycling are discussed. A special flow-through CDI cell containing activated carbon fiber (ACF) electrodes was developed for this purpose. Ex situ XPS measurements were conducted to prove the presence of oxidized surface groups on the positive electrode of these cells due to cycling. A surprising phenomenon that looks like an inversion functionality of the carbon electrodes occurring after numerous charge–discharge cycles is observed and explained.

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In this paper we report on attempts to improve the efficiency of electrochemical capacitive deionization (CDI) by understanding the relevant ion adsorption processes. Specially designed three-electrode cells were elaborated to study the relationship between the charge injected and the charge efficiency of the adsorption/desorption of Na+ and Cl− ions onto highly porous, high surface area carbon cloth electrodes. The counter electrodes in these cells were large reversible Ag–AgCl electrodes. Knowing the volume and concentration of the solution and the charge and mass balance of the working and counter electrodes, the degree of cation and anion adsorptions onto the working electrode could be calculated separately as a function of the applied potential. The relevance of these data to the design of a symmetric CDI cell is briefly discussed.

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Capacitive deionization (CDI) is a method in which charged species can be electro-adsorbed by imposed electrostatic forces formed by polarization of high surface carbon electrode. An important parameter that may have pronounced effect on the desalination performance in CDI processes is the potential of zero charge (PZC) of the carbon electrodes in the cell. In this work we examined the influence of the relation between the electrodes' PZC and the electrodes' potential (Vs. Ref. electrode) when the cell is being shortcircuited (E 0 ) at dynamic steady state, on the salt removal effectiveness. A flow through CDI cell, which solution's concentration could be continuously measured in the course of the periodic charge-discharge processes was employed for this purpose. The paper outlines guidelines for CDI cells optimization by choosing appropriate carbon electrodes.

Using potential perturbation techniques, we investigated the kinetics of electroadsorption processes of ions with different dimensions and different concentrations into activated carbon electrodes with various porous structures. We found that the ratio between the pore size and the ion size is of great significance in terms of electroadsorption kinetics. Microporous carbon fiber electrodes exhibited a lower charging rate as compared with mesoporous aerogel carbon. The use of activated aerogel electrodes with a fractal structure composed of both micro- and mesopores, was found to be the best for effective electroadsorption due to both high electrical double layer capacity obtained and high rates of electroadsorption. We also explored the kinetics of electroadsorption processes into molecular sieve carbon electrodes, demonstrating that, despite the hindered adsorption processes into these electrodes, it is possible to obtain effective deionization by using them for selective water desalination processes.