Electrode Material For Capacitive Deionization Research Articles

Electroadsorption Desalination Performance of Carbon Materials Derived from Coconut Shell without Membrane Separation

This study investigated coconut shells, an abundant and low-cost raw material, as the precursor for activated carbon preparation, and applied a carbonization activation method to prepare carbon materials under different activation conditions. The differences in the performance of biomass derived carbon materials as capacitive deionization (CDI) electrodes were studied under conditions of different activators, activator doses, and activation temperatures. Compared with commercial coconut shell activated carbon, studies have shown that biomass derived carbon electrodes obtained under the optimal preparation conditions of NaOH as the activator, a carbonizer to activator ratio of 1:3, and an activation temperature of 800 ℃ have an excellent electro adsorption performance and the potential to be used as a CDI electrode material. The salt adsorption capacity (SAC) of activated carbon made with coconut shell derived carbon materials after 20min of electro adsorption reached a maximum of 11.47mg/g. After 10 repeated uses, its SAC remained at the original 90.58%, demonstrating an excellent cycling stability.

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.

Optimization of Desalination Efficiency and Exploratory Applications of TiO2 Active Site Electrode Enhanced by Activated Carbon and Tween 80 in Capacitive Deionization Technology.

Capacitive deionization (CDI) is an emerging desalination technology for seawater desalination. The development of high-desalination and long-life electrode materials is a research focus in the global water treatment field. In this experiment, Tween T80 was used as a surface activator, and a modified electrode was prepared by facilitating the deposition of TiO2 active sites onto the surface of activated carbon through a sol-gel/hydrothermal two-step synthesis strategy. The morphology and specific surface area of the composite material were analyzed through scanning electron microscopy, specific surface area measurements, and contact angle tests. The results indicated that the sol-gel/hydrothermal two-step synthesis strategy played a crucial role in the homogeneous combination and performance enhancement of the composite material. Under constant voltage mode, when the working voltage was 1.2 V, the desalination capacity of this composite material in a NaCl solution with an initial conductivity of 3000 μS·cm-1 reached 23.8 mg·g-1 (26% higher than materials prepared by conventional sol-gel methods). After 150 cycles, the capacity retention rate was 78%, and the retention capacity was significant (87%). Overall, the results demonstrate the potential of the sol-gel/hydrothermal two-step synthesis strategy in preparing high-performance CDI electrode materials. The modified electrode prepared using this method offers enhanced desalination capacity and durability, making it a promising candidate for seawater desalination and other water treatment applications.

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.

Critical review of capacitive deionization: design, operation consideration and real-world environmental applications

Capacitive Deionization (CDI) has emerged as a promising and environmentally sound solution for addressing pressing water treatment challenges. This critical review meticulously examines the design, operational considerations, and performance metrics of CDI systems, particularly highlighting their significance in environmental applications under real-world conditions for handling different water sources such as groundwater, surface water, sea water. Various CDI configurations, electrode materials, and operational parameters are scrutinized through an extensive analysis of literature, with their direct influence on system efficiency, ion removal capacities, and long-term stability being elucidated. The reduced energy consumption, minimal chemical usage, and potential for sustainable water treatment of CDI, as compared to traditional methods, are emphasized from an environmental perspective. Moreover, this review underscores the pivotal role of CDI in practical environmental applications, including desalination, wastewater treatment, and remediation of inorganic pollutants (heavy metals and hardness) and resource recovery (nutrient, uranium, lithium…). By presenting compelling case studies, CDI's efficacy in mitigating environmental impacts is illustrated, offering a cleaner and more cost-effective alternative to conventional treatment methods. By outlining challenges and charting future directions, this review serves as a roadmap for researchers, engineers, and policymakers, facilitating the development of sustainable and efficient water treatment strategies. In an era marked by escalating environmental concerns, CDI emerges as a potential technology for responsible and effective water management, poised to shape a more sustainable future.

Surface functional modification of Nb2CTx MXene for high performance capacitive deionization

MXene, show a promising electrode material for capacitive deionization (CDI) due to their elevated conductivity and hydrophilic surface characteristics. Despite optimal electrochemical reaction conditions, MXene still exhibits unsatisfactory capacity. Enhancing capacitance in Nb2CTx MXene poses a key challenge, and addressing this involves leveraging pseudocapacitance through increased active site concentration. This study reports a method to notably improve the capacitance by incorporating cation intercalation and surface modification. After alkali treatment and thermal annealing, the obtained 400-KOH-Nb2C as a cathode in capacitive deionization, exhibiting notable salt adsorption capacity of 104.2 mg g−1 at 1.6 V and an efficient removal rate of 1.73 mg g−1 min−1, cyclic stability maintained over 200 cycles. This optimized electrochemical and desalination performance is due to the large interlayer spaces of Nb2CTx and the surface with lowest termination of -F and –OH group, promoting the delicate surface of Nb2CTx MXene and accelerating ion transport. Furthermore, the derivation of KNbO3 nanowires on 400-KOH-Nb2C surface further expands the layer spacing of MXene and enhances the active sites, and also acts as a protective layer to improve the stability of Nb2C, this effectively addressing challenges associated with desalination. This study offers a novel solution for improving Nb2CTx MXene electrochemical properties in CDI.

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.

Charged functional groups modified porous spherical hollow carbon material as CDI electrode for salty water desalination

As a new electrochemical technology, capacitive deionization (CDI) has been increasingly applied in environmental water treatment and seawater desalination. In this study, functional groups modified porous hollow carbon (HC) were synthesized as CDI electrode material for removing Na+ and Cl− in salty water. Results showed that the average diameter of HC was approximately 180 nm, and the infrared spectrum showed that its surface was successfully modified with sulfonic and amino groups, respectively. The sulfonic acid functionalized HC (HC-S) showed better electrochemical and desalting performance than the amino-functionalized HC (HCN), with a maximum Faradic capacity of 287.4 F/g and an adsorptive capacity of 112.97 mg/g for NaCl. Additionally, 92.63% capacity retention after 100 adsorption/desorption cycles demonstrates the excellent stability of HC-S. The main findings prove that HC-S is viable as an electrode material for desalination by high-performance 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+.

Hydrogen-Bonded Organic Framework Derived 2D N, O Co-Doped Carbon Nanobelt with Tunable Pseudocapacitive Contribution for Efficient Capacitive Deionization.

Defect engineering is recognized as an attractive method for modulating the electronic structure and physicochemical characteristics of carbon materials. Exploiting heteroatom-doped porous carbon with copious active sites has attracted great attention for capacitive deionization (CDI). However, traditional methods often rely on the utilization of additional heteroatom sources and strong corrosive activators, suffering from low doping efficiency, insufficient doping level, and potential biotoxicity. Herein, hydrogen-bonded organic frameworks (HOFs) are employed as precursors to synthesize N, O co-doped porous carbon via a simple and green reverse defect engineering strategy, achieving controllable heavy doping of heteroatoms. The N, O co-doping triggers significant pseudocapacitive contribution and the surface pore structure supports the formation of the electric double layer. Therefore, when HOF-derived N, O co-doped carbon is used as CDI electrodes, a superior salt adsorption capacity of 32.29±1.42mgg-1 and an outstanding maximum salt adsorption rate of 10.58±0.46mgg-1min-1 at 1.6V in 500mgL-1 NaCl solution are achieved, which are comparable to those of state-of-the-art carbonaceous electrodes. This work exemplifies the effectiveness of the reverse nitrogen-heavy doping strategy on improving the carbon structure, shedding light on the further development of rational designed electrode materials for CDI.

Oxygen-vacancy abundant δ-Bi2O3@PCNF anode for selective phosphate removal with exceptional capacity

Excessive phosphate concentration in waterbody will lead to eutrophication and deterioration of water quality. Capacitive deionization (CDI) is an environmental-friendly technique for ion removal, and the phosphate ions can be selectively removed and accumulated by designing the CDI electrode materials with specific phosphate bonding capability. Herein, a δ-Bi2O3-modified porous carbon nanofiber (δ-Bi2O3@PCNF) was constructed by solvothermal reaction in the presence of polyhydric alcohols. Due to abundant oxygen vacancies and high flexibility, the δ-Bi2O3@PCNF was used directly as a self-supporting CDI anode for selective phosphate adsorption. Under the optimized conditions, the adsorption capacity of phosphate arrived at 99.6 mg P/g in 50 mg P/L solution, and the adsorption maximum of 127.5 mg P/g was achieved according to Langmuir adsorption model. In the dual-anion solution containing PO43– and Cl–, the δ-Bi2O3@PCNF electrode still maintains the high selectivity, with a P separation factor of 22 (CPO43–/CCl– = 1:5, molar ratio) in PO43–/Cl– mixture. By using the δ-Bi2O3@PCNF-based CDI device, the actual paddy drainage has realized the ultralow phosphate concentration down to 0.03 mg P/L. The related mechanisms involved in phosphate adsorption on δ-Bi2O3@PCNF were proposed. This work demonstrates the great potential of CDI technology for low-concentration phosphorus recovery, owing to the high selectivity of the δ-Bi2O3@PCNF electrode material.

A lamellar chitosan-lignosulfonate/MXene nanocomposite as binder-free electrode for high-performance capacitive deionization

Ti3C2Tx (MXene) is considered as a superior electrode material for capacitive deionization (CDI) due to its high conductivity and two-dimensional structure. However, the electrochemical performance of pristine MXene nanosheets has been significantly impeded by the surface oxidation in the aqueous media and re-stacking caused by van der Waals forces which reduces the ions storage capacity. In this study, the chitosan-lignosulfonate/MXene (CLM) composite was used as a binder-free electrode to enhance the ion storage capacity and long-run cycling stability for hybrid capacitive deionization (HCDI). The chitosan-lignosulfonate nanospheres were able to increase the interlayer spacing between the MXene nanosheets effectively, which has significantly enhanced the ion storage capacity and electrochemical properties of the electrode. The binder-free CLM cathode demonstrated a high salt adsorption capacity of 44.6 mg g−1 and a maximum average salt adsorption rate of 5.8 mg g−1 min−1 at 1.2 V. A high cycling stability above 97 % for 30 cycles was observed. Also, the long-term stability of CLM electrode was studied by X-ray photoelectron spectroscopy (XPS) and the results showed that the CLM electrode was not prone to surface oxidation after 30 cycles. This study can guide future development of high-performance 2D material composite electrodes for enhancing capacitive deionization efficiency.

Development of biochar electrode materials for capacitive deionization: Preparation, performance, regeneration and other challenges

Development of biochar electrode materials for capacitive deionization: Preparation, performance, regeneration and other challenges

Synergy of structural engineering and dual-heteroatoms co-doping engineering boosting porous carbon toward efficient capacitive deionization

Carbon materials have drawn increasing attention as promising electrode materials for capacitive deionization (CDI) on account of their excellent conductivity and high specific surface area. Nevertheless, the practical application of conventional carbon materials has been significantly impacted by the limited desalination capacity and the slow desalination rates. Herein, a series of hierarchical porous nitrogen and sulfur co-doped carbons (PNSC-X, X = 2.5, 5, and 7.5) were successfully prepared by combining the salt template method with the dual-heteroatoms co-doping method. Benefiting from the suitable degree of graphitization, the unique hierarchical porous structure (micropores-mesopores-macropores) and the synergistic effect between the nitrogen/sulfur (N/S) dual-dopant, the optimized electrode (PNSC-5) demonstrates an abundance of active sites and rapid reaction kinetics, which are conducive to remarkably improving the CDI performance. In consequence, as a promising electrode material for CDI, the PNSC-5 exhibits excellent desalination performance (39 mg g−1 under 1.2 V), outstanding salt adsorption rate (3.23 mg g−1 min−1) and eminent stability. The CDI device with PNSC-5 as electrode shows low energy consumption and high charging efficiency during the cycle test. Furthermore, the corresponding desalination mechanism is systematically expounded by various characterization methods. This work provides a new inspiration for exploiting high-performance carbon materials for efficient electrochemical desalination.

Modulating the surfaces functional groups and defects in carbon via salt template method for high-performance capacitor deionization

Conventional carbon-based materials have been widely applied for capacitive deionization (CDI) because of their excellent electrical conductivity and specific surface area. The surface functional group and defect of carbon materials have a critical impact on CDI performance. Hence, a hierarchical mesoporous/macropores carbon (MPC) with abundant quinone functional groups (C = O) and defects were synthesized by a salt template method. The introduction of C = O functional groups and defects not only effectively shortens the ions transport path, but also enhances the pseudocapacitive behavior of carbon materials. As a result, the MPC represents a fantastic desalting capacity of 31.3 mg g−1 for sodium salt (500 mg L–1 NaCl) at an applied voltage of 1.2 V. Meanwhile, the MPC also shows superior salt adsorption rate and great cycling performance. In addition, the desalination mechanism was analyzed in detail by systematic ex-situ measurements. Here, this work presents a novel perspective for designing high-performance carbon-based CDI electrode materials.

Mesoporous dopamine-modified leaf-like zeolitic imidazolate frameworks derived carbon for efficient capacitive deionization

The onstruction of novel porous carbon materials for efficient desalination is crucial but remains challenging for capacitive deionization (CDI) development. Herein, a micelle-assisted strategy was raised to coat mesoporous polydopamine (mPDA) on the surface of two-dimensional (2D) leaf-like zeolitic imidazolate frameworks (ZIFL) followed by confinement pyrolysis. The introduction of the mPDA layer can not only mitigate the backbone collapse of ZIFL during pyrolysis to build a favorable porous environment for efficient ion transport and diffusion, but also induce explosive growth of carbon nanotubes (CNTs) to improve the electron conductivity. As expected, the derivative ZIFL@mPDA-C possessed a high desalination capacity of 41.9 mg g−1 in 500 mg L-1 NaCl solution at an operating voltage of 1.2 V. In particular, the retention ratio of the desalination capacity of ZIFL@mPDA-C was about 100 % after 50 consecutive adsorption-desorption cycles, while its leaf-like morphology and hierarchical pore structures were well preserved. This study highlights the importance of rationally designed structures and components for the performance breakthrough of carbon-based CDI electrode materials.

Hierarchical nickel cobaltite nanoneedle arrays armored flexible electrospinning carbon nanofibers membrane for electrochemical deionization

Crafting an ideal capacitive deionization (CDI) cathode presents a significant challenge, owing to the myriad requisites it must fulfill. These entail a high specific capacitance, commendable conductivity, stability, and the counteraction of the shortcomings inherent in additive/binder electrodes. Realizing all these attributes from a single-component material, however, is a daunting task. In this investigation, we present our findings on the in-situ cultivation of ultrathin NiCo2O4 nanoneedle arrays on freestanding electrospinning nitrogen-enriched carbon nanofibers devised to tackle these hurdles. The resultant material boasts remarkable features that not only alleviate tension triggered by phase transition but also accentuate electric conductivity. Electrochemical evaluations authenticate the effectiveness of structural modulation, reflected through a markedly augmented specific capacitance, superior stability, and diminished electrochemical resistance. Furthermore, the assembled pliable, asymmetric CDI cell incorporating electrospinning carbon nanofiber showcases superior desalination capabilities (38.86 mg g−1 at 1.2 V), a swift desalination rate (0.65 mg g−1 min−1), and improved cycle stability. This work finding contribute valuable interpretations towards proficiently designing and developing advanced CDI electrode materials capable of meeting the stringent requisites for high specific capacitance, good conductivity, and stability. It further propels progress towards industrialization, thereby expediting the realization of practical applications.

High-performance nitrogen-doped porous carbon electrode materials for capacitive deionization of Industrial salt-contaminated wastewater

The increasing demand for efficient and sustainable solutions in the field of energy storage and water desalination has sparked research in the development of supercapacitors and capacitive deionization (CDI) cells. This study presents a scalable and eco-friendly process for the preparation of N-doped polyhedral macrotube carbon arrays with a multihole cross-sectional profile. These arrays were synthesized from lotus stems (N-ALS) through carbonization at 500 °C and activation at 700 °C. The resulting material offers a high density of adsorption sites and good conductivity, making it suitable for use as electrodes in both supercapacitors and CDI cells. The N-ALS electrodes exhibit a high specific capacitance of 221.34 F g−1 at a scan rate of 2 mV s−1 and excellent cycling stability, as well as a salt adsorption capacity (SAC) of 26.07 mg g−1 at an applied voltage of 1.4 V and 85 % retention after 50 desalination-regeneration cycles in CDI cells, outperforming traditional activated carbon electrodes.

Flexible ultrathin Nitrogen-Doped carbon mediates the surface charge redistribution of a hierarchical tin disulfide nanoflake electrode for efficient capacitive deionization

Constructing pseudocapacitive electrodes with high specific capacities is indispensable for increasing the large-scale application of capacitive deionization (CDI). However, the insufficient CDI rate and cycling performance of pseudocapacitive-based electrodes have led to a decline in their use due to the corresponding volumetric expansion and contraction that occurs during long-term CDI processes. Herein, hierarchical porous SnS2 nanoflakes are encapsulated inside an N-doped carbon (NC) matrix to achieve efficient CDI. Benefiting from the synergistic properties of the pseudocapacitive SnS2 nanoflakes and few-layered N-doped carbon, the heterogeneous interface simultaneously provides more available vigorous sites and demonstrates rapid charge-transfer kinetics, resulting in a superior desalination capability (49.86 mg g−1 at 1.2 V), rapid desalination rate (1.66 mg g−1 min−1) and better cyclic stability. Computational research reveals a work function-induced surface charge redistribution of the SnS2@NC heterojunction, which can lead to an auspicious surface electronic structure that reduces the adsorption energy to improve the diffusion kinetics toward sodium adsorption. This work contributes to providing a thoughtful understanding of the interface engineering between transition metal dichalcogenides and NC to construct high-performance CDI electrode materials for further industrialization.