Electrode Material For Capacitive Deionization Research Articles

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.

Nano-manganese oxide and reduced graphene oxide-incorporated polyacrylonitrile fiber mats as an electrode material for capacitive deionization (CDI) technology.

Capacitive deionization (CDI) is a trending water desalination method during which the impurity ions in water can be removed by electrosorption. In this study, nano-manganese dioxide (MnO2) and reduced graphene oxide (rGO)-doped polyacrylonitrile (PAN) composite fibers are fabricated using an electrospinning technique. The incorporation of both MnO2 and rGO nanomaterials in the synthesized fibers was confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The electrochemical characteristics of electrode materials were examined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and constant current charge–discharge cycles (CCCDs). The specific capacitance of the PAN electrode increased with increasing MnO2 and rGO contents as well as when thermally treated at 280 °C. Thermally treated composite fibers with 17% (w/w) MnO2 and 1% (w/w) rGO (C-rGOMnPAN) were observed to have the best electrochemical performance, with a specific capacitance of 244 F g−1 at a 10 mV s−1 scan rate. The electrode system was used to study the removal of sodium chloride (NaCl), cadmium (Cd2+) and lead (Pb2+) ions. Results indicated that NaCl showed the highest electrosorption (20 472 C g−1) compared to two heavy metal salts (14 260 C g−1 for Pb2+ and 6265 C g−1 for Cd2+), which is most likely to be due to the ease of mass transfer of lighter Na+ and Cl− ions; When compared, Pb2+ ions tend to show more electrosorption on these fibers than Cd2+ ions. Also, the C-rGOMnPAN electrode system is shown to work with 95% regeneration efficiency when 100 ppm NaCl is used as the electrolyte. Hence, it is clear that the novel binder-free, electrospun C-rGOMnPAN electrodes have the potential to be used in salt removal and also for the heavy metal removal applications of water purification.

Carbon nanofiber@ZIF-8 derived carbon nanosheet composites with a core–shell structure boosting capacitive deionization performance

This work demonstrated the development of a hierarchical porous carbon–carbon composite used as an electrode material for capacitive deionization.

Novel MoS2/NOMC electrodes with enhanced capacitive deionization performances

Capacitive deionization (CDI) is a promising technology for seawater and brackish water desalination but still suffers from several drawbacks, such as low electrosorption capacity and less efficient desalination performance. In this study, MoS2/NOMC (nitrogen-doped highly ordered mesoporous carbon) composite with enhanced hydrophilicity, conductivity and capacitance was successfully synthesized by a hydrothermal process. The MoS2/NOMC electrodes showed efficient desalination performances with an electrosorption capacity of 28.82 mg/g at 1.6 V in 250 mg/L NaCl solution and a maximum electrosorption capacity of 30.49 mg/g based on Langmuir fitting. The mechanism of the enhanced desalination performance of MoS2/NOMC electrodes was explored through the characterization of the contributions of the capacitor-controlled (electrical double layer capacitor without charge transfer) and diffusion-controlled processes (charge transfer with N-doping of NOMC as well as the various oxidation states (from + 2 to + 6) of molybdenum atoms (Mo) in MoS2). Capacitor-controlled process played a major role (with the contribution of 73.17%) for the improved desalination performances of MoS2/NOMC electrodes compared to the diffusion-controlled process (with the contribution of 26.83%). In addition, MoS2/NOMC electrodes showed an excellent regeneration performance, indicating the potential of MoS2/NOMC composite as a promising CDI electrode material.

TiO2/Activated Biochar Hybrid Material Prepared By Ultrasonication and Heat Treatment for Capacitive Deionization

TiO2-doped activated biochar was successfully prepared as a hybrid electrode material for capacitive deionization. The introduction of TiO2 has the advantages of low cost, high chemical stability, hydrophilicity, and eco-friendliness. Activated biochar was treated with titanium isopropoxide (TTIP) and isopropyl alcohol solution by an ultrasound assisted process followed by calcination at 400 °C. The physical and chemical properties of the resulting material was characterized by XPS, XRD, SEM, and TEM. Cyclic voltammetry was performed to analyze the electrochemical properties of the prepared electrodes. Furthermore, the performance of TiO2-biochar electrode was evaluated in a 3D-printed CDI cell and the salt removal capacity was examined using a chloride ion-selective electrode. It was shown that the removal capacity was enhanced from 5.1 mg/g NaCl (activated biochar) to 8.6 mg/g NaCl. The increase in capacity is associated with a better wettability of the electrode, which increases the number of surface-active sites and promotes a more efficient ion diffusion inside the biochar pores. This result is beneficial to improve biochar application as an inexpensive alternative electrode material with metal oxide modification.

A Review of Battery Materials as CDI Electrodes for Desalination

The world is suffering from chronic water shortage due to the increasing population, water pollution and industrialization. Desalinating saline water offers a rational choice to produce fresh water thus resolving the crisis. Among various kinds of desalination technologies, capacitive deionization (CDI) is of significant potential owing to the facile process, low energy consumption, mild working conditions, easy regeneration, low cost and the absence of secondary pollution. The electrode material is an essential component for desalination performance. The most used electrode material is carbon-based material, which suffers from low desalination capacity (under 15 mg·g−1). However, the desalination of saline water with the CDI method is usually the charging process of a battery or supercapacitor. The electrochemical capacity of battery electrode material is relatively high because of the larger scale of charge transfer due to the redox reaction, thus leading to a larger desalination capacity in the CDI system. A variety of battery materials have been developed due to the urgent demand for energy storage, which increases the choices of CDI electrode materials largely. Sodium-ion battery materials, lithium-ion battery materials, chloride-ion battery materials, conducting polymers, radical polymers, and flow battery electrode materials have appeared in the literature of CDI research, many of which enhanced the deionization performances of CDI, revealing a bright future of integrating battery materials with CDI technology.

Faradaic Electrodes Open a New Era for Capacitive Deionization.

Capacitive deionization (CDI) is an emerging desalination technology for effective removal of ionic species from aqueous solutions. Compared to conventional CDI, which is based on carbon electrodes and struggles with high salinity streams due to a limited salt removal capacity by ion electrosorption and excessive co‐ion expulsion, the emerging Faradaic electrodes provide unique opportunities to upgrade the CDI performance, i.e., achieving much higher salt removal capacities and energy‐efficient desalination for high salinity streams, due to the Faradaic reaction for ion capture. This article presents a comprehensive overview on the current developments of Faradaic electrode materials for CDI. Here, the fundamentals of Faradaic electrode‐based CDI are first introduced in detail, including novel CDI cell architectures, key CDI performance metrics, ion capture mechanisms, and the design principles of Faradaic electrode materials. Three main categories of Faradaic electrode materials are summarized and discussed regarding their crystal structure, physicochemical characteristics, and desalination performance. In particular, the ion capture mechanisms in Faradaic electrode materials are highlighted to obtain a better understanding of the CDI process. Moreover, novel tailored applications, including selective ion removal and contaminant removal, are specifically introduced. Finally, the remaining challenges and research directions are also outlined to provide guidelines for future research.

Hydrangea-like nitrogen-doped porous carbons derived from NH2-MIL-53(Al) for high-performance capacitive deionization

Capacitive deionization (CDI), as an effective and eco-friendly technology to solve the issue of freshwater scarcity, is limited to implement practical application because of the low adsorption capacity of electrode materials. Exploring a novel and high performance electrode material is still crucial for CDI research. In this work, hydrangea-like nitrogen-doped porous carbons (HNPCs) have been successfully prepared by using NH2-MIL-53(Al) as precursor. Benefiting from large surface area (1369 m2·g−1) and high nitrogen content, the porous carbon carbonized at 900 °C (HNPC-900) exhibits an excellent electrochemical performance and a high adsorption ability of 21.17 mg·g−1 in 500 mg·L−1 NaCl solution at the applied voltage of 1.2 V. Meanwhile, 15 adsorption–desorption cycles suggest HNPC-900 electrode possesses renewability. This work demonstrates that HNPC-900 could be a promising electrode material for CDI and provides a strong support for the application of carbon materials derived from NH2-MIL-53(Al) in CDI field.

Subsize Ti3C2Tx derived from molten-salt synthesized Ti3AlC2 for enhanced capacitive deionization

Ti3C2Tx is a promising intercalation-type electrode material for capacitive deionization (CDI). However, Ti3C2Tx, obtained from traditional synthesized Ti3AlC2, is with large particle size and undersized interlayer space, which can easily lead to the longer ion diffusion path, fewer adsorption sites, and higher ion diffusion barrier in CDI process. In this work, subsize and Na+ intercalated Ti3C2Tx (Na+-Ti3C2Tx-MS) was prepared by HF etching KCl-assisted molten-salt synthesized Ti3AlC2 and following NaOH treatment. The Na+-Ti3C2Tx-MS achieves a high electrosorption capacity of 14.8 mg/g and a high charge efficiency of 0.81 at the applied voltage of 1.2 V in 100 mg/L NaCl solution. Besides, the stable desalination performance of Na+-Ti3C2Tx-MS has been confirmed. The superior performance of Na+-Ti3C2Tx-MS can be attributed to the subsize particle and larger interlayer space. Both two factors can effectively increase ions adsorption sites, shorten diffusion path lengths, and reduce diffusion barriers in the CDI process.

Cobalt and nickel ferrites based capacitive deionization electrode materials for water desalination applications

Capacitive deionization (CDI) is an emerging technology for water desalination and is based on electrosorption of ions onto surfaces of electrically charged electrodes. The CDI electrode materials play a significant role in determining the process efficiency. In this study, pure and mixed nickel-cobalt ferrites CoxNi1-xFe2O4 (x = 0.0, 0.3, 0.5, 0.7 and 1.0) were synthesized using the sol-gel auto-combustion method and investigated as novel CDI electrode materials. The purity, structure, and morphology of the synthesized ferrite nanoparticles were analyzed by various techniques. The electrochemical performance of the synthesized materials was investigated, and the results showed that the mixed ferrite Co0.5Ni0.5Fe2O4 electrode possessed the highest specific capacitance of 255 F/g at a scan rate of 10 mV/s. The electrodes were used to treat 250 mg/L NaCl solution in a CDI cell at 1.2 V and a feed flow rate of 10 mL/min. Under optimized experimental conditions, the highest specific salt adsorption capacity was 21.84 mg/g, corresponding to 23.43% of NaCl removal efficiency. These electrodes were highly stable and easily regenerable with less than 5% loss in electrosorption capacity for six adsorption/desorption cycles. The recyclability, stability, and enhanced electrochemical performance of the fabricated electrodes establish cobalt-nickel ferrites as a promising material for use in CDI desalination application.

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

Capacitive deionization (CDI) has attracted considerable interest as an energy-efficient and cost-effective approach for water desalination. The fundamental working principle of CDI relies on ion electrosorption on the surface of a pair of electrically charged electrodes. Therefore, the development of more efficient electrode materials with high salt adsorption capacity is at the heart of CDI technology, and has motivated considerable efforts over the past decade. In particular, various carbon materials, including conventional activated carbon and various forms of porous carbon and graphene, have been intensively investigated as the CDI electrode materials for their electrochemical stability and large surface area, which typically relies solely on ion absorption and the formation of Helmholtz electrical double layer. It has more recently been shown that significant improvements in salt adsorption capacity can be further achieved either by functionalization of carbon surface with redox-active groups, or by introducing electrochemically active transition metal oxides or conductive polymers into the carbon matrix. Herein, we briefly summarize the fundamental principle of CDI technology, and review the recent progress in the design and development of high performance CDI electrode materials. We will conclude with a brief perspective on the current challenges and future opportunities in CDI technology. • The ion storage mechanisms of electric double layer (EDL) materials and intercalation materials. • Summary of the recent progress in the design and development of high performance CDI electrode materials. • Summary of the fundamental principle of CDI technology. • We outlined some important issues/challenges for the development of CDI electrode materials.

Enhanced electrochemical and capacitive deionization performance of metal organic framework/holey graphene composite electrodes

In this paper, we designed and prepared a novel metal organic framework (MOF)/holey graphene (HG) composites as electrode materials for electrochemistry and capacitive deionization (CDI). The MOF nanoparticles were attached to the surface of the HG sheets to form layered porous structure, which promoted the transport of ions and electrons in the electrode/electrolyte interfaces. Additionally, the synergistic effect of these composite electrodes, which combined pseudocapacitance performance of MOF and the high conductivity of graphene, contributed to enhancing the performance of electrochemistry and CDI. The MOF/HG-2 exhibited high capacitances of 526 F g−1 at current rates of 0.1 A g−1, low charge transfer resistance of 0.53 Ω, and excellent cycling stability (retention of about 90.3% after 5000 cycles at 2 A g−1). As electrode materials for CDI, the MOF/HG-2 displayed a remarkable electrosorption capacity of 39.6 mg g−1 with initial salt concentration of 800 mg L−1, and there was no obvious attenuation after 20 CDI regeneration cycles. These results confirmed that MOF/HG was a promising electrode material for the actual application of CDI.

Nitrogen and fluorine co-doped 3-dimensional reduced graphene oxide architectures as high-performance electrode material for capacitive deionization of copper ions

• Nitrogen and fluorine doped 3-D reduced graphene oxide (rGO) through hydrothermal route was prepared. • High capacitive deionization of Cu 2+ ions by 3D-NFrGO when applied in capacitive electrode material. • Chemisorption and ion diffusion onto electrode govern the Cu 2+ ion removal. • Heteroatoms doping, good surface area and pore structure result in high specific capacitance. Heavy metal ions pose a threat to human life as their consumption can be hazardous. In this regard, unprecedented interests towards the development of technology for water purification have been witnessed. The present work is yet another novel attempt to develop a promising nanomaterial for the removal of Cu(II) from aqueous media using fast and facile capacitive deionization (CDI) method. Nitrogen- and fluorine- co-doped 3-dimensional reduced graphene oxide (3D NFrGO) architectures were developed via a hydrothermal route at 180 °C for 12 – 24 h and then applied as CDI electrode for Cu(II) removal. The fabrication of NFrGO at 180 °C for 16 h shows excellent 3D structures with high specific surface area of 182.7 m 2 g −1 and bimodal pore size distribution at 2.1 and 5.6 nm, which can facilitate rapid ions/electrons transport inside the interconnected mesoporous channels. In addition, the doping of heteroatoms can not only increase the conductivity, but also create the vacancy defect of NFrGO, resulting in accelerated electrochemical performance. The specific capacitance of 245.6 F g −1 was also achieved, demonstrating the high capacitive features of the as-obtained material. Moreover, a high percent removal of 95% and specific electrosorption capacity of 52.4 mg g −1 at 100 mg L -1 Cu(II) was obtained. Electrosorption results can be well-described by the pseudo second-order adsorption kinetics and the intraparticle diffusion model, which signify that chemisorption and ion diffusion into electrode pores govern Cu(II) removal. Results obtained in this study have demonstrated that N, F-co-doped 3D rGO can be a promising CDI material for efficient removal of heavy metal ions as well as for water purification.

Amorphous boron phosphide nanosheets: A highly efficient capacitive deionization electrode for uranium separation from seawater with superior selectivity

Boron phosphide nanosheets were synthesized by direct chemical reaction of B2H6 and PCl3 at ambient temperature, facilitated by use of plasma in an ionic liquid. The material possessed excellent specific capacity of 179.3 F g−1, large specific surface area (221.7 m2 g−1), and an average thickness of 8.422 nm. It can serve as an electrode material for capacitive deionization to extract U(VI) ions from aqueous solution at concentrations ranging from 0.05 to 130 mg L−1, with a maximum adsorption capacity of 2584 mg g−1. The excellent performance of these boron phosphide nanosheets is mainly due to their special structural features and ability to strongly coordinate with uranium, which facilitates the electrosorption process. This material also demonstrated superior selective adsorption characteristics for U(VI) ions over other competing metal ions (Sr2+, Ba2+, VO3−, Cr3+, Ca2+, Co2+, Cu2+, Mn2+, Mg2+, Ni2+, Fe3+, Na+, and K+) present in natural seawater. Boron phosphide nanosheets offer potential as a novel and potent electrode material to extract uranium from seawater using capacitive deionization technology.