Capacitive Deionization Performance Research Articles

Optimization of the intermediate chamber improves desalination performance in flow electrode capacitive deionization (FCDI): A comparative study

Flow electrode capacitive deionization (FCDI), a novel ion removal technology, is influenced by various factors such as electrode material properties, fluid flow rate, and device structure. In the FCDI system, the intermediate chamber is the core element where ions migrate towards the cathode and anode to complete the adsorption process. In this study, we designed a hollow plastic plate with channels (PP) and a hollow graphite plate with channels (GP) as the intermediate chamber, compare and study with conventional plastic mesh (PM) chambers. CFD simulations revealed that the newly designed PP and GP chambers significantly reduced the hydraulic stagnation zone. The results of the desalination experiments revealed that the desalination efficiency of the GP-FCDI was 1.5 and 1.9 times higher than that of the PP-FCDI and PM-FCDI, respectively. At the same time, in situ potential measurement (ISPM) was used to monitor the voltage drop of each component in FCDI, thereby accurately calculated the proportion of energy consumption in the intermediate chamber. The results indicate that the energy consumption of the intermediate chamber of GP-FCDI was 54 % less than that of PM-FCDI. The current work will help us provide new insights for the design and optimization of FCDI systems.

Bendable, lamellar MXene membrane electrodes with diverse diffusion pathways for potential application in miniaturized capacitive deionization devices

Flexible devices have shown great application potential in portable and miniaturized devices. However, work on flexible electrodes for capacitive deionization (CDI) has not been well developed due to the issues of desalination property, processability, and availability under actual bending conditions. Herein, we constructed a kind of flexible lamellar MXene membrane by assembling Ti3C2Tx sheets with both crumpled and perforated structures and studied their desalination performance in conventional planar and bent configurations. The crumpled and perforated features in Ti3C2Tx (C-P-TC) nanosheets could optimize the in-plane and out-of-plane diffusion channels of the stacked samples, respectively, effectively improving the accessibility of membranes. As a result, the desalination performance of such C-P-TC electrodes was superior to that of those assembled from crumpled or perforated sheets alone. Significantly, this flexible C-P-TC electrode still showed excellent performance at real bend deformation, which possessed not only almost the same CDI capacity as the traditional planar configuration but also good cycling stability. This work not merely proposes an alternative strategy to improve the CDI performance of lamellar MXene electrodes by regulating the nanostructures of channels but also confirms their effective deionization ability under real bent state, greatly facilitating the potential use of flexible electrodes in miniaturized CDI devices.

Pore structure and N/F bifunctional groups in hierarchical porous carbons via spontaneous silica etching for enhanced capacitive deionization performance

This study presents a novel, one-step synthesis of nitrogen and fluorine bifunctional hierarchical porous carbons (HPCs) for capacitive deionization (CDI). The method involves co-gelation of silica and polyvinylidene fluoride, followed by pyrolysis for efficient silica removal. This method eliminates the need for toxic solvents and extensive cleaning steps. Optimized HPCs exhibit a high surface area (1464.71 m2/g) with abundant mesopores. Electrochemical analysis reveals a specific capacitance of 179.5F/g. In the CDI process using 500 mg/L NaCl solution, the HPCs demonstrate exceptional performance with a high salt adsorption capacity (24.61 mg/g) and a fast average adsorption rate (3.69 mg/g/min). This performance is attributed to the combined effects of the hierarchical pore structure facilitating rapid ion adsorption and the N/F bifunctional groups enhancing electrosorption ability. This work offers a one-step, solvent-free method for synthesizing HPCs with superior desalination performance and demonstrates the synergistic effect of pore structure and N/F bifunctional groups.

Scaling behavior of Si in capacitive deionization (CDI) systems for brackish groundwater desalination

Capacitive deionization (CDI) is a potentially cost-effective method of desalinating brackish groundwaters though the technology has not yet been widely utilised for this particular application. Silicon (Si) is a common element in groundwaters which may cause problems due to its tendency to induce severe fouling of equipment used for water treatment. In this study we focus on the impacts of the presence of Si on the performance of CDI. A systematic evaluation procedure is proposed, which is used to distinguish the “dynamic” and residual Si scaling and the impacts of these types of fouling on desalination performance. Results show that Si has minimal influence on CDI performance within low concentration ranges (<0.5 mM). Sorption of deprotonated silicic acid species is largely avoided in CDI, which contributes to sustaining the removal of major ions and stable operation of the system. However, at high concentrations of Si (>2.0 mM), scaling was observed to form on the electrode surface, leading to noticeable deterioration in CDI electrode performance. The presence of ion exchange membrane in CDI (i.e., membrane CDI or MCDI) can significantly alleviate Si scaling of the desalination system. Results of this study clearly demonstrate the scaling behavior of CDI and its derivatives when dealing with Si-laden water matrices, providing insights into the design and maintenance of CDI systems in practical applications.

Go-encapsulated La-doped lithium manganese oxide assemblies to enhance lithium extraction performance in capacitive deionization

The electrochemical lithium extraction technique from brine has emerged as a key strategy in addressing the issue of lithium resource scarcity. Lithium manganese oxide (LMO) stands out as a typical lithium-ion selective material. Nevertheless, its lithium extraction application is restricted by inadequate conductivity and limited cycling stability. In this report, through a simple electrostatic self-assembling method, a 3-dimensional (3D) GO/La-LMO hybrid was fabricated wherein La-doped LMO (La-LMO) was enveloped by graphene oxide (GO) nanosheets. The resultant GO/La-LMO exhibited a significantly improved electrochemical behavior with fast Li+ diffusion rate and high conductivity. The GO/La-LMO hybrid demonstrated outstanding selectivity for the electrochemical intercalation/de-intercalation of Li+. As a Li+-selective cathode in capacitive deionization (CDI) device, the GO/La-LMO electrode achieved a high Li+ adsorption capacity of 1.33 mmol g−1 (10 mM LiCl) and superior selectivity with a separation factor of 126 (Mg2+/Li+ = 30, molar ratio) in Mg2+/Li+ mixed solution. The Li+ extraction percentage reached 80.4 % in the simulated salt-lake brine. Crucially, the GO/La-LMO electrode substantiated prominent structural stability and low Mn dissolution over 100 cycles, attributed to the synergistic effect of La-doping and GO capsulation to mitigate Jahn-Teller distortion. In addition, the selective adsorption–desorption mechanism of Li+ was confirmed. This work introduces a facile approach for the fabrication of robust carbon-based LMO hybrids, demonstrating the potential applications as high-performance lithium-selective materials.

A novel ε-MnO2/MXene composite as an electrode with excellent conductivity and ultrahigh capacitive deionization

Manganese dioxide (MnO2) holds great promise as an electrode material for capacitive deionization (CDI); but its low electrical conductivity considerably restricts its desalination capacity. Nevertheless, its electrochemical performance can be enhanced by augmenting its conductivity. Hence, we propose a novel strategy for constructing a strongly coupled ε-MnO2/MXene composite, in which, MXene (Ti3C2Tx) serves as a network of electron conduction highways that enhance the charge transfer of ε-MnO2 and activates the underutilized electrochemically active sites of ε-MnO2. Based on these advantages, an ε-MnO2/MXene composite is prepared for the first time, comprising spherical ε-MnO2 nanoparticles grown on MXene layers. As demonstrated, ε-MnO2/MXene composite demonstrates exceptional desalination performance, exhibiting a maximum deionization rate of 17.54 mg g−1 min−1 and an ultrahigh desalination capacity of 114.66 mg g−1 in 1000 mg/L NaCl solution at 1.2 V, which is considerably higher than those observed for ε-MnO2 (74.93 mg g−1), MXene (29.26 mg g−1) and recently reported electrode materials. Such an outstanding CDI performance can be ascribed to a considerably high specific capacitance ε-MnO2/MXene composite of approximately 337.2F g−1 at a specific current of 1 A/g, which is approximately 2.16 times that of an ε-MnO2 electrode.The excellent performance of ε-MnO2/MXene composite makes it a potential practical application of CDI.

Sodium lignosulfonate/graphene composites for efficient desalination by incorporating CoS to control pore size

The phenomenon of overlapping double layers due to micropores inhibits capacitive deionization performance, which is improved by increasing the pore size. In this study, a novel ternary composite electrode (sodium lignosulfonate/reduced graphene oxide/cobalt sulfide, LGC) was designed using a two-step hydrothermal method. CoS with high pseudocapacitance modifies sodium lignosulfonate and graphene connected by hydrogen bonding, benefiting from the constitutive steric structure. The electrochemical performance was significantly enhanced, and the desalination capacity substantially improved. The LGC electrode specific capacitance was as high as 354.47 F g−1 at a 1 A g−1 current density. The desalination capacity of the capacitive deionization device comprising LGC and activated carbon in 1 M NaCl electrolyte reached 28.04 mg g−1 at an operating condition of 1.2 V, 7 mL min−1. Additionally, the LGC electrodes degraded naturally post the experiment by simply removing the CoS, suggesting that the LGC composites are promising material for capacitive deionization electrodes.

Simultaneously improving surface area and hydrophilicity of biomass activated carbon for achieving superior desalination performance in CDI

Super activated carbon is a promising electrode material for capacitive deionization (CDI), an emerging sustainable desalination technology. Increasing its CDI performance requires improving hydrophilicity while maintaining high specific surface area. Traditionally this is challenging, but modifying super activated carbon with earth-abundant metal ions at room temperature can achieve both aims through a low-energy process aligned with sustainability. The modified super activated carbon showed higher specific surface area, improved hydrophilicity, and enhanced desalination performance. Particularly, the salt adsorption capacity of Cu2+-modified super activated carbon in 500 mg/L NaCl solution at 1.2 V increased from 35.4 mg/g to 49.3 mg/g, among the highest for sustainable carbon materials. The capacity increase was enabled by simultaneously increasing specific surface area and hydrophilicity through themetal modification process. Along with high charge efficiency (93.4%), fast adsorption rate, and good cycling stability (80% capacity retention over 50 cycles), the modified super activated carbon displayed superior overall desalination performance. This study exemplifies how sustainable design principles can be applied to synthesize high-performance CDI electrode materials, through green chemistry and engineering for optimized efficiency.

Simultaneous removal of sulfamethazine and sulfate via electrochemical oxidation and capacitive Deionization: Mechanisms of in-situ activation and strategies of the hybrid system

Electrochemical oxidation (EO) is a well-established method for pollutants removal. However, excessive addition of oxidant during EO may cause secondary pollution. Moreover, the unprocessed ions in the wastewater can cause further contamination. This research introduces a hybrid process that combines EO with capacitive deionization (CDI), in situ catalytically utilizing sulfate (SO42-) and removing sulfamethazine (SMZ). This process realized by layered porous MXene-modified biochar electrodes (BCM) that demonstrate electrocatalytic and adsorption properties. The electrochemical oxidation system, constructed using BCM cathode and boron-doped diamond anode, harnesses in situ generation of oxidants from SO42-, leading to the complete degradation of 30 mg/L sulfamethazine in 30 min through adsorbed radicals and metastable active species at the biphasic interface. Subsequently, the BCM-2 exhibits excellent CDI performance at 1.2 V, achieving a desalination capacity of 15.40–65.97 mg/g in 100–1000 mg/L Na2SO4 solution. By combining EO with CDI, BCM simultaneously removes sulfamethazine and sulfate, resulting in a 60 % reduction in total organic carbon and a 14.4 % decrease in electrical conductivity after one process cycle. Moreover, BCM exhibits favorable cytocompatibility.

Rational design of Core-Shell heterostructured CoFe@NiFe Prussian blue analogues for efficient capacitive deionization

Rational design of stable and high-capacity faradaic electrode materials is crucial for enhancing the desalination performance of hybrid capacitive deionization (HCDI). In this work, to fully exploit the advantages of high-capacity CoFe Prussian blue analogs (PBA) and structurally stable NiFe PBA, a core–shell heterostructured CoFe@NiFe PBA is successfully synthesized by a two-step co-precipitation method. The construction of the core–shell heterostructure not only suppresses dissolution of the CoFe PBA core, but also facilitates fast charge transfer and efficient ion diffusion during Na+ ions insertion/extraction. With an optimal NiFe PBA shell thickness of 30 nm, the core–shell structured PBA electrode demonstrates outstanding cycling performance with a capacity retention of 72.6 % over 10,000 charge/discharge cycles. Moreover, when utilized as the cathode material in HCDI, the core–shell heterostructured PBA exhibits intriguing desalination performance, including a high desalination capacity of 49 mg g−1 and excellent desalination stability over 200 cycles (77.7 %). This paper presents a straightforward strategy for designing core–shell heterostructured PBA electrode, with the potential to advance the development of high-performance capacitive desalination.

Enhancing capacitive deionization performance and cyclic stability of nitrogen-doped activated carbon by the electro-oxidation of anode materials

Enhancing capacitive deionization performance and cyclic stability of nitrogen-doped activated carbon by the electro-oxidation of anode materials

The influence of flow electrode channel design on flow capacitive deionization performance: Experimental and CFD modelling insights

Flow capacitive deionization (FCDI) is an emerging desalination technology at which flow electrodes (shear-thinning flowable carbon slurries) are used to remove ions from saline water. The geometry of flow electrode channels, which provide the path and ensure the distribution and mixing of the flow electrodes, is one of the most important aspects to be optimized. This work presents experimental and computational fluid dynamics (CFD) modelling analysis of the influence of the geometry of flow electrode channels on FCDI performance. Flow electrode gaskets (with open, serpentine (short) horizontal and serpentine (long) vertical channels) were 3D printed using a polyethylene terephthalate glycol (PET-G) filament. The FCDI cell with a vertical serpentine flow electrode channel exhibited the poorest performance due to channel blockage by carbon particles, while the best results were achieved with a horizontal serpentine flow electrode channel. CFD simulations aided in understanding this behaviour by showing that the channel geometry strongly affects the local shear rate, and thus the local viscosity of flow electrodes. Thus, it is recommended to design channels that induce flow disturbance aiming for increasing the shear rate and hence reducing flow electrode viscosity, therefore promoting their flowability and reducing clogging chances.

Research progress of sodium super ionic conductor electrode materials for capacitive deionization

The world is suffering from water shortage and the hope relies on the desalination of salty water. Several technologies are available for desalination such as reverse osmosis and electrodialysis. However, the application of these technologies in desalination is limited by the higher energy consumption, high investment and maintenance costs. Capacitive deionization (CDI), an up-coming technology at an infant stage is able to supplement the dwindling freshwater resources and provide water to the population. The performance of CDI is directly affected by the electrode materials. Since its inception carbon has been the principal electrode materials for CDI technology. However, low salt removal capacity due to inaccessibility of nanopores and ejection of co-ions hinder the application of carbon materials. Battery materials have been developed as an alternative to accompany carbon materials. Specifically, sodium superionic conductor (NASICON) materials have been used in brackish water desalination by CDI due to having the diffusion channels forming a three dimensional open structure and availability at low cost. However, the NASICON materials have not yet applied in the desalination of water with high salinity such as sea water. This paper reviews the present status of NASICON materials as CDI electrode materials and fairly compares it with carbon materials. It further compares the cost of NASICON and carbon materials, highlights the possibility of NASICON to desalinate high ionic strength solutions such as seawater. Moreover, the paper, discuss the methods which can be used to enhance the salt removal capacity of NASICON materials and provide examples of NASICON materials in the field of energy storage that can be borrowed and used in CDI. From the analysis of this work, NASICON materials are great companion of the carbon materials, are cost effective and are promising for the desalination of sea water.

Ultrathin nitrogen-doped carbon Ti3C2Tx-TiN heterostructure derived from ZIF-8 nanoparticles sandwiched MXene for high-performance capacitive deionization

Rational design of high-performance electrode materials is crucial for enhancing desalination performance of capacitive deionization (CDI). Here, ultrathin nitrogen-doped carbon/Ti3C2Tx-TiN (NC/MX-TiN) heterostructure was developed by pyrolyzing zeolite imidazolate framework-8 (ZIF-8) nanoparticles sandwiched MXene (ZSM), which were formed by assembling ultrafine ZIF-8 nanoparticles with size of 20 nm on both sides of MXene nanosheets. The introduction of ultrasmall ZIF-8 particles allowed for in situ nitridation of the MXene during pyrolysis, forming consecutive TiN layers tightly connected to the internal MXene. The two-dimensional (2D) heterostructure exhibited remarkable properties, including high specific surface area and excellent conductivity. Additionally, the resulting TiN demonstrated exceptional redox capability, which significantly enhanced the performance of CDI and ensured cycling stability. Benefiting from these advantages, the NC/MX-TiN exhibited a maximum adsorption capacity of 45.6 mg g−1 and a steady cycling performance in oxygenated saline water over 50 cycles. This work explores the rational design and construction of MXene-based 2D heterostructure and broadens new horizons for the development of novel CDI electrode materials.

Exploring a sustainable binder for capacitive deionization technology to achieve high salt and zinc ion removal efficiency

As a newly developed water purification technology, capacitive deionization (CDI) is a promising technology for water desalination. The influence of binders on the performance of CDI electrodes, especially on the performance of heavy metal ion removal, has been rarely discussed so far. On the other hand, searching sustainable materials to replace those made from non-renewable resources is attracting more and more attention. Herein, the influence of the sustainable binders on CDI performance is studied. For the NaCl adsorption, the chlorinated rubber (CLR) electrode shows a higher capacity and rate capability than the other binders. Particularly, we explored the CDI process for zinc ion in water and claimed that the formation of hydroxide of zinc ion should be considered. Surprisingly, CLR can inhibit Zn4SO4(OH)6•5H2O generation and structural disruption of electrode. CLR electrode has the highest desalination performance, 79.8 mg g−1 of ZnSO4 and the longest cycle lifetime remaining 95.4 % of adsorption capacity after 10,000 cycles. Moreover, CLR can be made from sustainable natural rubber and its price is only 14.3 % of PVDF. Obviously, CLR is promising for heavy metal salt removal and large-scale water purification devices. CLR also shows superior performance than PVDF in aqueous zinc capacitor.

The Utilization of Candlenut Shell-Based Activated Charcoal as the Electrode of Capacitive Deionization (CDI) for Seawater Desalination

Activated carbon or activated charcoal is one of the best materials that can be used as a constituent of CDI electrodes, not only because of its various advantageous properties but also because it can be sourced abundantly from plant waste. This research aims to determine the effect of the thickness of the candlenut shell activated charcoal electrode and the particle size of the activated carbon used on the capacitive deionization (CDI) performance in seawater desalination. Candlenut shell-based activated charcoal is obtained in three stages, namely preparation, carbonization, and activation. The carbonization stage was done by using a pyrolysis reactor at a temperature of 400°C for 8 hours. The activation was done with the activator of H3PO4 67%. The variation of thickness was 6 mm, 8 mm, 10 mm, and 15 mm while the variation of particle size was 60 mesh, 80 mesh, 100 mesh, and 200 mesh. The results showed that the higher capacitance was obtained with the thinner electrodes, where the best value was the thinnest electrode, 6 mm, which produced the highest capacitance, 122.96 nF. For the desalination of seawater, it is shown that the finest particle/smallest particle size will result in the best desalination performance, where 200 mesh particle size will result in the decrease of salinity from 34% to 4%. That is 88.23% decrease in salinity. Therefore, the using of candlenut shell-based activated carbon as the electrode in CDI is proven to be able to obtain good performance in seawater desalination.

3D interconnected porous graphene architecture as a high-performance capacitive deionization electrode

Capacitive deionization (CDI) is a promising technology for brackish water desalination because of its high efficiency, no secondary pollution and low cost. However, the ion removal capacity of CDI system for brackish water desalination is still insufficient. Herein, a new in-situ porous Cu template method is used to prepare a unique open three-dimensional mesoporous graphene foam (3DMG) with high CDI performance. The developed 3DMG material has rich mesoporous structure, interconnected pore structure, high specific surface area, good hydrophilicity and excellent electrical conductivity, which can achieve effective solution/pore contact, rapid ion migration and high electrosorption capacity. Therefore, the specific capacitance of 3DMG as high as 141.37F/g at 1 M NaCl and 10 mV/s, and the maximum salt adsorption capacity is as high as 32.08 mg/g (1000 mg/L, 1.2 V), which is significantly higher than that of graphene-based electrode materials reported in most literatures. It also shows excellent regeneration performance and stability after repeated electrosorption-desorption cycles. The developed 3DMG undoubtedly provides a promising electrode material platform for CDI devices, effectively solving the urgent problem of freshwater resource shortage.

Synthesis of nitrogen-doped carbon nanoboxes with pore structure derived from zeolite and their excellent performance in capacitive deionization

Synthesis of nitrogen-doped porous hollow carbon nanoboxes (HCNBs) with abundant hierarchical pores derived from zeolite for high performance capacitive deionization (CDI) applications.

Three-dimensional cross-linked sugarcane bagasse carbon material: A substitute for graphene with excellent performance in capacitive deionization and highly efficient Cu2+ removal

Capacitive deionization (CDI) is a high-performance, low-energy consumption, and environmentally friendly water treatment technology with a broad application prospect in heavy metal removal. Selecting electrode materials with high capacitance and low resistance is essential for improving CDI's desalting efficiency. This article discusses the utilization of sugarcane bagasse (C-N-X) and the production procedures of CDI materials. The unique 3D cross-linked structure of C-N-X provides excellent mass transfer properties and significant advantages in capacitance and conductivity. The results of X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectrometer (FTIR) show that bagasse biochar with graphene-like structure and abundant functional groups provides active sites for Cu2+ removal. In this paper, C-N-X is first used as CDI electrode material to remove Cu2+. Electrochemical tests show that the specific capacitance of C-N-X is still stable at about 47 F g−1, and the removal capacity of Cu2+ (25 mg L−1) reaches 66.79 mg g−1 within 4 h after 700 cycles. The experimental results and DFT calculations confirm the adsorption selectivity of C-N-700 for Cu2+.

Developing efficient, binder-free 3D porous Ti3C2Tx-MXene electrodes for enhanced capacitive deionization towards desalination

Research and design of high-performance Faraday electrode have always been a key to enhance the desalination performance of membrane capacitive deionization. This study developed a binder-free 3D porous Ti3C2Tx-MXene electrode by depositing Ti3C2Tx-MXene nanosheets uniformly onto the graphite electrodes through electrophoretic deposition, followed by a straightforward liquid‑nitrogen freezing and vacuum drying. Uniform-interconnected and conductive network structure of the electrode provided abundant active sites and promoted efficient ion diffusion and transport rate. High pseudocapacitance (287 F/g) and large surface area (16.4 m2 g−1) of the 3D porous electrode led to excellent desalination performance (59 mg g−1) and rapid desalination rate (0.55 mg g−1 s−1), substantially outperforming the conventional coated electrodes. This research provided technical support for the rapid development of capacitive deionization technology towards high-efficient desalination.