Understanding Capacitive Deionization Performance By Comparing Its Electrical Response with an Electrochemical Supercapacitor

ZiF-8 induced carbon electrodes for selective lithium recovery from aqueous feed water by employing capacitive deionization system

Capacitive deionization (CDI) is a class of electrochemical desalination technologies which desalinate via ion storage in electric double-layers. CDI has received renewed attention in recent years due to the ability to couple energy storage with salt separation. During galvanostatic operation, a current is applied between porous carbon electrodes until a limiting voltage is reach. The cell is then discharged by applying a reverse current, generating brine and recovering stored charge. However, CDI desalination and energy efficiency can be limited by parasitic side reactions, and selective adsorption of counter-ions (anions at the positive electrode, and cations at the negative electrode). Several material additions and electrode configurations have been proposed to overcome these limitations, with the most prominent being the addition of ion exchange membranes (IEMs) promote counter ion flux out of the desalination chamber and incorporation of carbon slurry electrodes to increase system adsorption capacity. Likewise, functionalization of carbon electrodes has been studied to improve counter-ion adsorption within EDL micropores. While the incorporation of functionalized carbon, IEMs in membrane capacitive deionization (MCDI), and the use of slurry electrodes in flow capacitive deionization (FCDI) have successfully reduced energy consumption or increased ion adsorption capacity in CDI systems, these modifications are often evaluated under limited conditions on the basis of specific performance enhancements. Additional clarity is necessary to evaluate the associated performance and cost tradeoffs across the design space. In this study, an equivalent circuit (M)CDI model, with porous electrode sub-models, was used to measure the sensitivity of CDI performance to material selection, design, and operating choices. In order to investigate the performance of FCDI, pulse-flowed electrodes of high capacity and electronic resistances were incorporated into the existing model. Similarly, fixed charge in the anodic and cathodic micropores was studied to investigate functionalized carbon. Constrained system parameters were randomly selected via latin hypercube sampling (LHS) across multiple electrode geometries and influent salt concentrations. The resultant model outputs were then correlated with input values to quantify parameter sensitivity. Our sensitivity analysis shows that operating current density, electrode specific capacitance, contact resistance, and fixed charge density were the parameters which most significantly dictated (M)CDI performance. These parameters where then used to construct an operational space for CDI, MCDI, and FCDI. The results of the sensitivity analysis and technology comparison were used to evaluate the current effectiveness of CDI technologies as well as near-term projections for improvements in material performance. Through this analysis we are able to set targets for performance and material properties necessary for each CDI configuration to favorably operate.

Capacitive deionization (CDI) is a potential technique for water treatments such as brackish water desalination, seawater desalination, wastewater remediation, and water softening. CDI has more advantages over other desalinating processes: (i) the technique works by the process of electroabsorption, and is even more energy-efficient, as it does not require any high-pressure pumps; (ii) as the module works in 0.8–2.0 V. An ideal electrode for CDI system requires the following characteristics: (i) large surface area; (ii) high porosity (both meso and micropores); (iii) high electrical conductivity; (iv) electrochemical stability; (v) bio-inertness; (vi) fast adsorption-desorption kinetics; (vii) good wetting behavior; (viii) low cost; and (ix) scalability. In Vietnam, coconut shell-derived activated carbon is produced by a calcinated process under nitrogen gas, which exhibits a high surface area (800-1000 m2/g). In this work, we prepared the CDI composite electrode based on coconut shell-derived activated carbon and high conductive carbon like CNTs or carbon black in the pilot scale. CDI systems with a capacity of 1 m3 per day were fabricated and monitored the desalination performance in Mekong Delta.

With the gradually increasing requirement for freshwater, capacitive deionization (CDI) as a burgeoning desalination technique has gained wide attention owing to its merits of easy operation, high desalination efficiency, and environmental friendliness. To enhance the desalination performance of CDI, different CDI architectures are designed, such as membrane CDI, hybrid CDI, and flow-electrode CDI. However, these CDI systems have their own drawbacks, such as the high cost of membranes, capacity limitation of carbon materials and slurry blockage, which severely limit their practical application. Notably, rocking-chair CDI (RCDI) composed of symmetric electrode materials delivers excellent desalination performance because of its special dual chamber structure, which can not only break through the capacity limitations of carbon materials, but also deliver a continuous desalination process. Although RCDI showcases high promise for efficient desalination, few works systematically summarize the advantages and applications of RCDI in the desalination field. This review offers a thorough analysis of RCDI, focusing on its electrode materials, structure designs and desalination applications. Furthermore, the desalination performances of RCDI and other CDI architectures are compared to demonstrate the advantages of RCDI and the prospect of RCDI is elucidated.

Chloride pre-intercalated CoFe-layered double hydroxide as chloride ion capturing electrode for capacitive deionization

Nonlinear dynamics of ion concentration polarization in capacitive deionization

Electrical double layers as ion reservoirs: applications to the deionization of solutions

Construction and evaluation of a novel three-electrode capacitive deionization system with high desalination performance

Capacitive deionization is an emerging electrochemical technology employed in water desalination applications. Multiple water desalination technologies include reverse osmosis, multi-stage flash, humidification-dehumidification, and nanofiltration. Capacitive deionization is appreciably increased the desalination efficiency compared to other technologies while promising energy-efficient and cost-effective operation. In the CDI system, the charged ions are extracted from feedwater by applying an electrical voltage across electrodes, in which the charged ions are attracted to the oppositely charged electrodes. This paper demonstrates the concept of capacitive deionization (CDI), the components of CDI cell, working principal, and performance metrics for the CDI system. Furthermore, the paper reviews the state of technology of the CDI cell and the development of the system since the mid-1960, including the concepts of membrane and flow electrode CDI. Finally, a cost analysis framework of CDI, MCDI, and FCDI is demonstrated based on the Levelized cost of water.

Ternary-metal Prussian blue analogues as high-quality sodium ion capturing electrodes for rocking-chair capacitive deionization

Recent progress in graphene-based and ion-intercalation electrode materials for capacitive deionization

High speed capacitive deionization system with flow-through electrodes

Capacitive deionization (CDI) is an emerging energy efficient, low-pressure and low-cost intensive desalination process that has recently attracted experts’ attention. The process is to explain that ions (cations and anions) can be separated by a pure electrostatic force imposed by a small bias potential. Even at a rather low voltage of 1.2 V, desalinated water can be produced. The process can be well operational by a professional cell design. Although various processes have been manufactured before, in this study, membrane was removed and a new unit was designed and manufactured (Using CFD Simulation). In this case, the combination of activated carbon powder (with an effective surface area of 2600 m2 per gram), carbon black, and polyvinyl alcohol with a ratio of 35/35/30 coated on carbon paper as electrode materials was considered for tests. The weight was 1.41 grams for each material, and the thickness was 0.44 mm. CDI system was tested, and the results of charge-discharge cycles, cyclic voltammetry, and impedance spectroscopy were evaluated. It can be implied that there is no need for a strong pump and, also, pressure drop can be reduced due to such a noticeable space between two electrodes. Preliminary experimental results showed high specific capacitance (2.1 Farad) and ultra-high salt adsorption capacity, compared with similar cases.

Intrinsic tradeoff between kinetic and energetic efficiencies in membrane capacitive deionization

Capacitive deionization (CDI) has shown great promise as a water treatment and conditioning technique. However, a large majority of studies using this technology have focused solely on NaCl removal, while other ions commonly found in natural waters might pose unaddressed challenges for CDI, such as specific adsorption, diffusional limitations and scaling precipitation. For instance, precipitation of inorganic salts such as calcium carbonate is an issue associated with brackish waters and RO plants. Similarly, high concentrations of sulfate and silicate salts in groundwater may lead to membrane scaling due to their low solubility [1]. Therefore, there is still a need to identify the effect of both individual ions and mixtures on CDI performance. In this work, calcium and sulfate sorption was studied using a CDI reactor outfitted with low-cost, high surface area carbons coated with two different metal oxides (SiO2 on the cathode and Al2O3 on the anode). The metal oxide coatings were chosen because of previous efforts in the literature showing improved electrode performance in the CDI process with the addition of these coatings [2-4]. Two calcium and two sodium salts (CaSO4, CaCl2, NaCl and Na2SO4) were tested to examine and compare the sorption characteristics of different anions and cations. Previous testing of this CDI system in a “Single Pass” (passing the water through the device only once) operational mode using a CaSO4 solution showed reductions in both Ca2+ and SO4 2- concentrations [5]. However, issues related with ion desorption and faradaic reactions (due to high cell potentials) were also observed. In this work, cycles of consecutive adsorption/desorption tests were performed to evaluate the long-term performance of this CDI system. Ion sorption and electrode stability were analyzed in terms of variables such as influent concentration, flow rate, and regeneration potential. These analyses also included performance metrics related with charge efficiency and energy consumption. For comparison purposes, CDI cells with uncoated carbon electrodes were evaluated following similar protocols. The results showed that increasing the concentration of CaSO4 in the feed solution (from 1.5 to 4.5 mM) increased the ion removal to values up to 3.29 ± 0.25 mg·g-1 and reduced energy consumption from 0.16 down to 0.09 kWh·mol-1. It was also observed that electric charge efficiencies increased by 15-30 % when asymmetrically coated configurations were employed. Nevertheless, the presence of SO4 2- significantly hindered salt desorption; conversely, recovery values close to 95 % were achieved using NaCl electrolyte. Finally, the evaluation of the long-term CDI performance revealed a slight but progressive loss in the ion electrosorption capability, probably due to the oxidation of the positive electrodes.