Electrode Material For Capacitive Deionization Research Articles

Mesopore dominated capacitive deionization of N-doped hierarchically porous carbon for water purification

Under the global shortage of freshwater resources, capacitive deionization (CDI) has attracted widespread attention as an efficient and energy-saving water purification technology. Herein, N-doped hierarchically porous carbons (NPCs) with micro-meso-macropore, excellent specific capacitance (194.75 F g−1), large specific surface area (1903.0 m2 g−1), high mesoporous content, and fast ion transport capability were prepared by the pyrolysis of polyacrylonitrile using nano-silica and ZnCl2 as pore-making agents. As CDI electrode materials for desalination and heavy metal adsorption, the optimized NPC-0.75 electrode delivered a maximum electrosorption capacity of 19.61 mg g−1 at the optimum operating parameters (1.2 V, 10 mL min−1, 500 mg L-1 NaCl) and an excellent regeneration performance after continuous electrosorption-desorption cycles. The structure–activity relationship analysis indicated that the mesopore dominates the CDI performance of NPCs in water. In addition, NPC-0.75 electrode showed a high removal capacity for Cu2+ (36.3 mg g−1), Cd2+ (30.02 mg g−1) and Pb2+ (21.5 mg g−1) in water. This study provides new insight into the design of high-efficiency porous carbons toward the CDI from water.

Highly efficient capacitive desalination for brackish water using super activated carbon with ultra-high pore volume

Activated-carbon-electrodes are widely used in capacitive deionization (CDI). However, the desalination capacity of most activated carbons remains to be improved, which makes it necessary to explore activated carbons with special structure and improved desalination capacity. In this context, we studied the desalination performance of super activated carbons with ultra-high total pore volume (VTot). This carbon showed a salt adsorption capacity of 27.2 mg/g in 500 mg/L NaCl solution at 1.2 V, which ranked among the highest value ever reported for activated carbons. The high adsorption capacity was due to the large VTot caused by the abundant presence of both micropores and mesopores in the material. The adsorption capacity of the carbon after 10 adsorption-desorption cycles (saturated adsorption capacity) was as high as 67.6 mg/g, which was dominated by VTot and water contact angle. The sample also showed excellent desalination rate and superior charge efficiency (76.5%). This study indicated that superior desalination performance could be obtained by using super activated carbon with high pore volume as a CDI electrode material.

Bio-composite nanoarchitectonics for graphene tofu as useful source material for capacitive deionization

The development of low cost, naturally sustainable, and high-performance electrode materials is the primary issue that determines the large-scale application of capacitive deionization (CDI). In this work, the nitrogen-doped activated porous carbon decorated by 3D interconnected graphene (NAPC/G) was synthesized by pre-carbonization and KOH activation of soy milk and graphene oxide composite gel (graphene tofu). The NAPC has an ultra-high specific surface area (SSA) of 2993.5 m2 g−1, rich micro-mesoporous structure, and good hydrophilicity. In addition, the 3D graphene network enhances the conductivity of the composite. Therefore, benefited from the synergetic effect of abundant ions adsorption sites and improved conductivity, the specific capacitance of NAPC/G electrodes is up to 370 F g−1 and maintains capacitance retention of 97% after 3000 cycles. For CDI electrode materials, the salt adsorption capacity (SAC), desalination rate, and cycle stability are the three important parameters. In this work, the NAPC/G electrode achieves an high SAC of 38.5 mg g−1, large desalination rate of 6.6 mg g−1 min−1 and good cycle stability that desalination performance remains 93.5% after 50 cycles. This research provides an effective way to promote the sustainable large-scale application of CDI.

Exceptional capacitive deionization desalination performance of hollow bowl-like carbon derived from MOFs in brackish water

As a bright technology for desalinating brackish water, the desalination ability of capacitive deionization (CDI) has been limited by the electrode materials. However, it was still a challenge to adjust the construction of CDI electrode material to improve the salt removal ability. Here, nitrogen-doped hollow bowl-like carbon (HBC) has been successfully constructed in ZIF-8 by facile templating approaches. Physical measurements displayed that HBC had a hollow bowl-like structure, a certain number of nitrogen-containing groups and high specific surface area (1244 m2 g−1). These unique features made HBC have high capacitance (210.7F g−1), remarkable cycle stability and low charge transfer resistance in electrochemical double layer capacitors, indicating its promising application in CDI desalination. Due to the abundant ion accumulation active sites and rapid ion diffusion of HBC materials, provided by unique characteristics of regular hollow bowl-like structure, microporous dominated structure, interconnected channels and nano-scale wall thickness, HBC showed high salt removal ability of 28.06 mg g−1 with 1.2 V in 0.5 g L-1 NaCl solution. Besides, HBC exhibited excellent average salt ion adsorption rate (1.56 mg g−1 min−1) and initial salt adsorption capacity of 90% after 20 cycles.

Two‐Dimensional MXene‐Polymer Heterostructure with Ordered In‐Plane Mesochannels for High‐Performance Capacitive Deionization

AbstractThe application of traditional electrode materials for high‐performance capacitive deionization (CDI) has been persistently limited by their low charge‐storage capacities, excessive co‐ion expulsion and slow salt removal rates. Here we report a bottom‐up approach to the preparation of a two‐dimensional (2D) Ti3C2Tx MXene‐polydopamine heterostructure having ordered in‐plane mesochannels (denoted as mPDA/MXene). Interfacial self‐assembly of mesoporous polydopamine (mPDA) monolayers on MXene nanosheets leads to the mPDA/MXene heterostructure, which exhibits several unique features: (1) MXene undergoes reversible ion intercalation/deintercalation and possesses high conductivity; (2) mPDA layers establish redox capacitive characteristics and Na+ selectivity, and also help to prevent self‐stacking and oxidation of MXene; (3) in‐plane mesochannels enable the smooth transport of ions at the internal spaces of this stacked 2D material. When applied as an electrode material for CDI, mPDA/MXene nanosheets exhibit top‐level CDI performance and cycling stability compared to those of the so far reported 2D materials. Our study opens an avenue for the rational construction of MXene‐organic hybrid heterostructures, and further motivates the development of high‐performance CDI electrode materials.

Two-Dimensional MXene-Polymer Heterostructure with Ordered In-Plane Mesochannels for High-Performance Capacitive Deionization.

The application of traditional electrode materials for high-performance capacitive deionization (CDI) has been persistently limited by their low charge-storage capacities, excessive co-ion expulsion and slow salt removal rates. Here we report a bottom-up approach to the preparation of a two-dimensional (2D) Ti3 C2 Tx MXene-polydopamine heterostructure having ordered in-plane mesochannels (denoted as mPDA/MXene). Interfacial self-assembly of mesoporous polydopamine (mPDA) monolayers on MXene nanosheets leads to the mPDA/MXene heterostructure, which exhibits several unique features: (1) MXene undergoes reversible ion intercalation/deintercalation and possesses high conductivity; (2) mPDA layers establish redox capacitive characteristics and Na+ selectivity, and also help to prevent self-stacking and oxidation of MXene; (3) in-plane mesochannels enable the smooth transport of ions at the internal spaces of this stacked 2D material. When applied as an electrode material for CDI, mPDA/MXene nanosheets exhibit top-level CDI performance and cycling stability compared to those of the so far reported 2D materials. Our study opens an avenue for the rational construction of MXene-organic hybrid heterostructures, and further motivates the development of high-performance CDI electrode materials.

Separation of Rare-Earth Ions from Mine Wastewater Using B12S Nanoflakes as a Capacitive Deionization Electrode Material.

In this study, nanoflakes of B12S were fabricated by plasma-assisted reaction of sulfur dichloride in an ionic liquid at room temperature using europium boride as a hard template. The nanoflakes had an average width and thickness of about 3 1urn and 9.6 nm, respectively, and a large specific surface area of 1197.2 m² g 1. They behaved like typical electric double-layer capacitors with a capacitance of 201.2 F g 1 at 0.2 mA cm ² During capacitive deionization to recover rare-earth ions, the nanoflakes had higher adsorption selectivity for Sm3+ than for other competing ions present in real mine waste water. This is due to the strong interaction of the electron-concentered S-groups (S''') of the nanoflakes with S m3+. This provides an alternative to construct efficient systems to specifically remove Sm3+ from aqueous solution using B12S nanoflakes. This process demonstrates that other boron sulfide compounds can be used to recover valuable ions by capacitive deionization.

Manganese ferrite decorated N-doped polyacrylonitrile-based carbon nanofiber for the enhanced capacitive deionization

In this study, the manganese ferrite was decorated onto 1-dimensional based activated carbon fiber (MnFe2O4/N-ACF) by precipitation method for capacitive deionization (CDI) application. Polyacrylonitrile (PAN) and 2-methylimidazole (2MI) were used as the carbon precursor and nitrogen dopant for the fabrication of 200 nm N-doped ACF (N-ACF). After the deposition of 5–15 wt% MnFe2O4 nanoparticles, the diameter of MnFe2O4/N-ACF increases to 300–400 nm, and the addition of 10 wt% MnFe2O4 can well deposits onto the surface of N-ACF to decrease the impedance to accelerate the electron transfer as well as to enhance the specific capacitance up to 422 F g−1 at 5 mV s−1. Furthermore, the CDI Ragone plots indicate that the specific electrosorption capacity (SEC) of NaCl by 10 wt% MnFe2O4/N-ACF is in the range of 23.4–41.2 mg g−1, which is a function of applied voltage, NaCl concentration, and flow rate. A SEC of 41.2 mg g−1 in the presence of 500 mg L−1 can be achieved when the flow rate and applied voltage are 10 mL min−1 and 1.4 V, respectively. Moreover, the as-prepared electrode materials can be recycled for at least 50 cycles and the SEC can be maintained over 93% of the original activity after 50 cycles, indicating the excellent cycling stability of MnFe2O4/N-ACF electrode. Results obtained in this study signify that the 1-D MnFe2O4/N-ACF is a promising CDI electrode material, which can provide a productive solution for elevating the platform with low cost and high efficiency for CDI technology.

Capacitive Deionization with Titania and Amine Modified Activated Biochar

Capacitive deionization based on electrosorption has become a viable process for brackish water desalination. In this study, activated biochar was employed as a low-cost carbon-based electrode material with comparable adsorption capacity to activated carbon and other biomass derived materials. Modification of the activated biochar was done by amine functional group grafting and metal oxide incorporation to improve ionic transport, and cation/anion selectivity, reducing the co-ion effect. Cation and anion selective electrodes were prepared by using titanium dioxide, and 3-aminopropyltriethoxysilane (3-APTES) via diazonium salt activation. These modified biochar electrodes were physically characterized by SEM-EDX, TEM, XPS, and XRD. Cyclic voltammetry, galvanostatic charge/discharge measurements, and impedance spectroscopy were performed to analyze the electrochemical property of both types of electrodes. This study investigated salt removal capacity of NaCl and NaF solutions using chloride and fluoride ion-selective electrode. Three different asymmetrical CDI cell designs (TB cathode – AmB anode, TB cathode – AcB anode, and AcB cathode – AmB anode) and two symmetrical cell designs AcB anode – AcB cathode and TB anode – TB cathode) were tested. Titania, amine, and activated biochar electrodes are denoted as TB, AmB, and AcB, respectively. It was found that a symmetric cell design with titania modified biochar electrodes show a 30% better removal capacity than the other cell designs. This work shows that biochar can be modified and explored broadly as an inexpensive alternative electrode material for capacitive deionization.

Recent Advances in Faradic Electrochemical Deionization: System Architectures versus Electrode Materials.

Capacitive deionization (CDI) is an energy-efficient desalination technique. However, the maximum desalination capacity of conventional carbon-based CDI systems is approximately 20 mg g-1, which is too low for practical applications. Therefore, the focus of research on CDI has shifted to the development of faradic electrochemical deionization systems using electrodes based on faradic materials which have a significantly higher ion-storage capacity than carbon-based electrodes. In addition to the common symmetrical CDI system, there has also been extensive research on innovative systems to maximize the performance of faradic electrode materials. Research has focused primarily on faradic reactions and faradic electrode materials. However, the correlation between faradic electrode materials and the various electrochemical deionization system architectures, i.e., hybrid capacitive deionization, rocking-chair capacitive deionization, and dual-ion intercalation electrochemical desalination, remains relatively unexplored. This has inhibited the design of specific faradic electrode materials based on the characteristics of individual faradic electrochemical desalination systems. In this review, we have characterized faradic electrode materials based on both their material category and the electrochemical desalination system in which they were utilized. We expect that the detailed analysis of the properties, advantages, and challenges of the individual systems will establish a fundamental correlation between CDI systems and electrode materials that will facilitate future developments in this field.

Stepwise hollow Prussian blue/carbon nanotubes composite as a novel electrode material for high-performance desalination

As a promising intercalation material for capacitive deionization (CDI), Prussian blue (PB) and its analogues (PBAs) have the superiority of high theoretical capacity and easy synthesis. But they often suffer from low conductivity and severe crystal phase transition, resulting in inferior desalination capacity and poor cycling stability. Herein, the dual strategy of structural optimization and carbon-based materials introduction is proposed to enhance the desalination performance of PBAs. Stepwise hollow structure formed by surface etching has been proved to be more outstanding than cubic structure. Enlarged the specific surface area, the contact area with the electrolyte increases, therefore, more active sites are exposed. Besides, the etching of external surfaces provides more buffer space, improves the tolerance to crystal phase transition, and enhances the cycling stability. The introduction of carbon nanotubes brings high conductivity. Specifically, the desalination test shows that stepwise hollow Prussian blue/carbon nanotubes composite delivers a high desalination capacity of 103.4 mg g−1 with outstanding cycling stability. Moreover, the low energy consumption of 0.23 Wh g−1 is also suitable for practical application. The dual strategy opens a window to design advanced electrode materials for CDI.

New green electrode materials derived from waste cigarette butts for capacitive deionization

Abstract Smoked cigarette butts are a non-biodegradable pollutant that has damaged the planet. However, carbon materials derived from cigarette butts have proven to be suitable for various applications. We synthesized cigarette butt-derived carbon via hydrothermal carbonization and chemical activation methods and then converted it to an electrode material for capacitive deionization. The fabricated material, SCC-750, exhibited a relatively high salt adsorption capacity of 10.27 mg g−1. The excellent CDI (capacitive deionization) performance is due to the high specific surface area of 3,093.10 m2 g−1 and a pore volume of 1.754 cm3 g−1. This work offers a new method to recycle harmful cigarette butts by converting them into promising electrode materials for capacitive deionization.

Achieving Enhanced Capacitive Deionization by Interfacial Coupling in PEDOT Reinforced Cobalt Hexacyanoferrate Nanoflake Arrays

Capacitive deionization (CDI) as a novel energy and cost‐efficient water treatment technology has attracted increasing attention. The recent development of various faradaic electrode materials has greatly enhanced the performance of CDI as compared with traditional carbon electrodes. Prussian blue (PB) has emerged as a promising CDI electrode material due to its open framework for the rapid intercalation/de‐intercalation of sodium ions. However, the desalination efficiency, and durability of previously reported PB‐based materials are still unsatisfactory. Herein, a self‐template strategy is employed to prepare a Poly(3,4‐ethylenedioxythiophene) (PEDOT) reinforced cobalt hexacyanoferrate nanoflakes anchored on carbon cloth (denoted as CoHCF@PEDOT). With the high conductivity and structural stability achieved by coupling with a thin PEDOT layer, the as‐prepared CoHCF@PEDOT electrode exhibits a high capacity of 126.7 mAh g−1 at 125 mA g−1. The fabricated hybrid CDI cell delivers a high desalination capacity of 146.2 mg g−1 at 100 mA g−1, and good cycling stability. This strategy provides an efficient method for the design of high‐performance faradaic electrode materials in CDI applications.

Carbon-embedded hierarchical and dual-anion C@MoSP heterostructure for efficient capacitive deionization of saline water

Recently, two-dimensional transition-metal disulfides (TMDs) with amazing chemical and physical superiorities are emerging as promising faradic ion intercalation materials for effective capacitive deionization (CDI) application. Herein, a carbon-embedded hierarchical and dual-anion C@MoSP nanoflowers was synthesized by a facile hydrothermal reaction accompanied by the phosphorization treatment, and explored as an advanced CDI electrode material. Benefiting from the specific microstructure (e.g., hierarchically porous arrangement, enriched porosity and highly open pore network) and the strong synergistic effect of highly conductive carbon and low-electronegativity P dopant, the C@MoSP electrode demonstrated high surface area, enrich accessible interlayer, superior ion diffusion pathway and good electric conductivity for effective salty ion intercalation/deintercalation; Accordingly, the C@MoSP electrode realized an outstanding gravimetric adsorption capacity of 25.43 mg/g, excellent intercalation rate, and good durability in a NaCl aqueous solution with an initial concentration of 500 mg/L at an operation voltage of 1.2 V, which were evidently enhanced in comparison to MoSP and pristine MoS2 ones.

A review of metal-organic framework-derived carbon electrode materials for capacitive deionization

A review of metal-organic framework-derived carbon electrode materials for capacitive deionization

Capacitive deionization and methyl orange removal of holey graphene hydrogels

In this study, we designed a new strategy to synthesize holey graphene hydrogel (r-HGH) using a one-step hydrothermal method by simultaneous reduction and etching. Based on this simple method, the holies on the graphene layers successfully inhibit the collapse of the graphene structure after the drying. Therefore, the r-HGH can form three-dimensional network structure with hierarchical holey. Using as a binderless supercapacitor electrode, the r-HGH exhibits a high specific capacitance of 451 F g−1 and low internal resistance of ~1.6 Ω. The capacitance can maintain 95.6% after 2000 cycles. Applying for capacitive deionization (CDI) for desalination and methyl orange removal, the r-HGH displays a desalination capacity as high as 44.44 mg·g−1 at voltage of 1.2 V with the initial NaCl conductivity of 1600 μS·cm−1, with the short adsorption/desorption equilibrium time of 200 s. Further, the r-HGH has obvious advantages for the electrosorption of charged organic ions. The electrosorption capacity for methyl orange is 57 mg·g−1, and the adsorption/desorption equilibrium time are within 200 s and 100 s, respectively. Thus, the high electrosorption capacity and rate for NaCl and methyl orang enables the r-HGH to be a promising electrode material for capacitive deionization and wastewater treatment.

Enhanced capacitive deionization performance of activated carbon derived from coconut shell electrodes with low content carbon nanotubes–graphene synergistic hybrid additive

With increasing desalination demand worldwide, electrode materials for capacitive deionization (CDI) have attracted extensive attention recently. To compete with Reverse Osmosis, the performance of CDI electrode still needs to be further enhanced. In this work, graphene (Gr)/carbon nanotubes (CNTs) conducting hybrid was dispersed at as low as 1 wt% in coconut shell derived activated carbon (AC) to fabricate cost effective and high performance electrode for brackish water CDI desalination. The fabricated AC/Gr/CNTs electrodes show an excellent performance with the capacitance of 60 F/g (at 5 mV/s), the salt adsorption capacity of 9.58 mg/g and salt adsorption rate of 1.51 mg/g min at 1.0 V in 200 ppm NaCl solution. It should be highlighted that owing to the synergistic effect, the role of hybrid additive (1 wt%) was demonstrated to be more effective than that of single one, from a technical as well as from an economical viewpoint. To our best knowledge, this is the first study reporting the application of ultra-low content AC/CNTs hybrid in AC based CDI electrodes.

One-pot synthesis of activated carbon decorated with ZnO nanoparticles for capacitive deionization application

• ZnO nanoparticles decorated activated carbon were prepared and used for CDI. • It exhibited high specific capacitance of 407.17 F/g at 10 mV/s. • The ACZn electrode shows high conductivity and desalination performance. A ZnO nanoparticles-decorated activated carbon (ACZn) nanocomposite was successfully fabricated via the hydrothermal method for efficient capacitive deionization. The as-fabricated ACZn material was characterized in terms of field emission scanning electron microscope-energy-dispersive X-ray spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy analysis and Brunauer─Emmett─Teller surface area analyses. These techniques revealed the formation of ZnO-decorated AC nanocomposite. The electrochemical performance of the fabricated ACZn nanocomposite as an electrode material for capacitive deionization was evaluated by cyclic voltammetry (CV), and impedance spectroscopy (EIS) tests in 1 M sodium chloride. The obtained results revealed that the fabricated ACZn nanocomposite exhibited higher specific capacitance (407.17 F/g) compared to AC (207.46 F/g) at the sweep rate of 10 mV/s. A desalination performance enhancement was obtained after the incorporation with ZnO nanoparticles and the electrosorptive capacity was 3.93 mg/g. This work will provide a novel electrode for capacitive deionization.

MnO2 decorated porous carbon derived from Enteromorpha prolifera as flow-through electrode for dual-mode capacitive deionization

Owing to fresh-water shortage, developing highly efficient capacitive deionization (CDI) system equipped with low-cost electrodes is urgently required to process saline water to freshwater. On the other hand, Enteromorpha prolifera (EP for short, a typical bio-waste in global oceans) induced marine ecological crisis has become a serious threat to the global marine ecosystem. Aiming to kill two birds with one stone, we report the design of an EP-derived MnO2-decorated activated carbon composite (ep-AC@MnO2) as low-cost electrodes for high-performance dual-mode capacitive deionization. The as-fabricated ep-AC@MnO2 displays a high specific capacitance of 335.6 F g−1 with dual-mode sodium storage behavior. Benefiting from this unique dual-mode capacitance feature, the ep-AC@MnO2-based dual-mode CDI system exhibits highly efficient desalination performance (desalination capacity/rate: 25.7 mg g−1/2.95 mg g−1 min−1) with excellent desalination recyclability (11.3% declination after 30 cycles). This work could be of broad interest since it not only exemplifies the simple fabrication of low-cost yet high-efficiency CDI electrode material with dual-mode capacitance for capacitive desalination, but also offers a sustainable strategy to turn marine biowaste into treasure for possible relieving of the EP-induced marine ecological crisis.

Large capacity and rapid rate of ion removal from synthetic municipal wastewater via CDI using chitosan-based nitrogen-doped porous carbon electrode

Capacitive deionization (CDI) technology has excelled in water treatment areas such as brackish water desalination, hard water softening and pollution ion removal. However, the poor performance of the electrodes used in CDI cell construction continues to limit its practical application. In this work, we used chitosan mixed with potassium hydroxide (KOH) and simply carbonized to synthesize porous carbon electrode materials (CTS-850) with excellent material and electrochemical performance, and achieve high adsorption capacity and fast adsorption rate in a variety of salt solutions. The material characterization of CTS-850 displayed super large specific surface area (>2300 cm3 g−1), pore volume and excellent nitrogen doping. Electrochemical characterization showed excellent specific capacitance, good conductivity and cycle performance. In CDI experiments, we explored the removal efficiency of electrodes carbonized under different temperatures in single and mixed solution systems, and the CTS-850 electrode had an ultra-high adsorption capacity of 47 mg g-1 and a fast adsorption rate of 6.7 mg g-1 min-1 in 15 mM synthetic municipal wastewater (～1750 mg L-1). In addition, we discussed the relationship between high adsorption capacity, fast adsorption rate and material properties. Our work is expected to provide guidance for the synthesis of higher performance CDI electrode materials.