Limitation of Charge Efficiency in Capacitive Deionization

Abstract

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.

Long term stability of capacitive de-ionization processes for water desalination: The challenge of positive electrodes corrosion

“…This RE could be also used as auxiliary electrode. The content of its AgCl layer was calculated [34] to be equivalent to more than 3 times the charge that can be stored in the electrical double layer of the electrodes in the cell (assuming 1 V was applied between the electrodes). A simpler cell which included three-electrode cell containing two sheets of ACF electrodes as the working electrode (WE) and two Ag/AgCl electrodes as the counter and reference electrodes, was also used (Fig.…”

“…Desalination of water by CDI can be operated in two modes related to the flow of solution in the cell: 'flow-by' [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], in which the solution flows in parallel to, between the electrodes and 'flowthrough' [34][35][36][37][38][39][40][41], in which the solution flows in perpendicular to, through the electrodes. Using the flow-through regime, the solution has to flow through macro-porous electrodes.…”

The Effect of Specific Adsorption of Cations and Their Size on the Charge-Compensation Mechanism in Carbon Micropores: The Role of Anion Desorption

“…As was recently demonstrated, the electrochemical quartz crystal microbalance (EQCM) technique [1][2][3] may serve as a true gravimetric probe of the compositional changes in micropores of activated carbons, providing unique information on the mechanism and kinetics of ion transport in these porous electrodes. [4] This information is crucially important, since rapid and reversible exchange of mobile species (ions, solvent molecules, and neutral species) between electrolyte solutions and porous carbon electrodes is of paramount importance for the development of efficient electrochemical supercapacitors, [5][6][7][8][9] (electro/ bio)chemical sensors, advanced modern membrane technologies (e.g., desalination), [10,11] and electronanofiltration. [12] In view of the plethora of ways in which physicochemical, surface, and porous structure characteristics of activated carbons can affect transport of mobile species, direct monitoring of the fluxes of the ionic carriers in these electrodes, resulting in their adsorption or desorption in carbon micropores, is an indispensable tool for elucidating the process-structure-property relationship in the above-mentioned technically important electrochemical systems.…”

Energy Consumption and Recovery in Capacitive Deionization Using Nanoporous Activated Carbon Electrodes

“…1 Due to its simplicity and reliability, capacitive deionization (CDI) has attracted a growing interest for water desalination. [1][2][3][4][5][6][7] Capacitive deionization utilizes highly porous electrodes to remove charged ions in water by electrosorption ( Figure 1). During charging, an electric voltage is applied and ions are driven to oppositely charged electrodes by electrostatic force and entrapped at the electrode-water interface by the formation of an electric double layer (EDL).…”