Desalination Using the Capacitive Deionization Technology with Graphite/AC Electrodes: Effect of the Flow Rate and Electrode Thickness

Abstract

Capacitive deionization (CDI) is an emerging water desalination technology whose principle lies in ion electrosorption at the surface of a pair of electrically charged electrodes. The aim of this study was to obtain the best performance of a CDI cell made of activated carbon as the active material for water desalination. In this work, electrodes of different active layer thicknesses were fabricated from a slurry of activated carbon deposited on graphite sheets. The as-prepared electrodes were characterized by cyclic voltammetry, and their physical properties were also studied using SEM and DRX. A CDI cell was fabricated with nine pairs of electrodes with the highest specific capacitance. The effect of the flow rate on the electrochemical performance of the CDI cell operating in charge–discharge electrochemical cycling was analyzed. We obtained a specific absorption capacity (SAC) of 10.2 mg/g and a specific energetic consumption (SEC) of 217.8 Wh/m3 at a flow rate of 55 mL/min. These results were contrasted with those available in the literature; in addition, other parameters such as Neff and SAR, which are necessary for the characterization and optimal operating conditions of the CDI cell, were analyzed. The findings from this study lay the groundwork for future research and increase the existing knowledge on CDI based on activated carbon electrodes.

Fabrication of Activated Carbon Decorated with ZnO Nanorod-Based Electrodes for Desalination of Brackish Water Using Capacitive Deionization Technology

“…The XRD pattern of the fabricated ZnO nanostructures contains six main diffraction peaks corresponding to the crystalline planes (100), (002), (101), (102), (110), and (103) (JCPDS 036-1451), ascribed to the hexagonal structure of ZnO wurtzite [ 30 ]. Moreover, the broad asymmetric diffraction peaks for AC were found at 2θ around 24° and 43°, which correspond to the (002) and (101) planes of crystalline hexagonal graphite (JCPDS 041-1487), respectively [ 31 ]. Finally, in the case of the AC/ZnO composite, its XRD diffractogram reveals the main characteristic peaks of zinc oxide, as well as a very weak and almost negligible peak corresponding to the (100) plane of AC, whereas the peak corresponding to (100) plane completely disappeared for the synthesized composite.…”

“…The results demonstrate that when the mass of ZnO utilized to fabricate the electrodes increases, the specific capacitance increases and the thickness of the electrodes decreases. This phenomenon can be described by the ion transportation theory, which establishes that as the thickness decreases, the transport of ions within the active layer is easier [ 31 , 32 ]. The highest value of specific capacitance calculated in this work was 135.7 F/g, obtained for the sample made with 9 g of ZnO (approximately 99 μm thickness), which is higher compared to that obtained for electrodes based only on activated carbon (69.4 F/g) calculated in our previous work [ 31 ].…”

“…This phenomenon can be described by the ion transportation theory, which establishes that as the thickness decreases, the transport of ions within the active layer is easier [ 31 , 32 ]. The highest value of specific capacitance calculated in this work was 135.7 F/g, obtained for the sample made with 9 g of ZnO (approximately 99 μm thickness), which is higher compared to that obtained for electrodes based only on activated carbon (69.4 F/g) calculated in our previous work [ 31 ]. The results show that the presence of ZnO nanorods in the matrix of CA electrodes increases its specific capacitance.…”

ReaxFF molecular dynamics of graphene oxide/NaCl aqueous solution interfaces

“…Many researchers suggested the graphene-based material as a unique material in the field of membrane development that could be used in the reverse osmosis system (RO) and more recently in capacitive deionization (CDI). [1][2][3][4][5] Graphene oxide is one of the graphene derivatives, and unlike graphene, GO exhibits good hydrophilicity, which is because of oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl groups in its plane and at the edges. There have been numerous studies on graphene or graphene oxide interfaces with water, yet an atomistic understanding of the water, ions, and GO interface, important for the development of GO for the water purification industry, is lacking.…”