Stability of a carbon gel electrode when used for the electro-assisted removal of ions from brackish water

A porous carbon gel obtained from the poly-condensation of resorcinol and formaldehyde was synthesized and used as an electrode material for the capacitive deionization (CDI) of synthetic brackish water. The desalting capacity of this material was evaluated in terms of applied voltage and zero-voltage regeneration over a number of cycles, and compared to that of commercially available carbon materials (powdered activated carbon and activated carbon cloth). Due to an adequate combination of chemical and porous features, the deionization capacity of the carbon gel electrode exceeded that of the electrodes based on conventional microporous carbons over a larger number of adsorption/regeneration cycles. An almost fully reversible ionic removal (ca. 90% recovery) was obtained for this electrode material when regeneration was carried out at zero-voltage conditions. Characterization of the cycled electrodes showed that the carbon gel was resistant to electrochemical anodic oxidation under the polarization conditions used (applied voltage of up to 1.2 V), whereas the electrodes produced from the two commercial carbon materials undergo severe modifications (oxidation and a decrease in surface area) when the applied voltage was maintained for several cycles.