Limitation of Charge efficiency in capacitive deionization: I. on the behavior of single activated carbon

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.