Capacitive Deionization Technology Research Articles

Fluoride removal using membrane capacitive deionization: The role of pH-dependent dissolved inorganic carbon

Defluorination technology is crucial for ensuring safe and accessible water. The application of capacitive deionization (CDI) technology faces challenges due to competitive adsorption of fluoride ions within complex natural fluoride-rich brackish water matrices, which often contain high levels of dissolved inorganic carbon (DIC) species (mainly HCO3– and CO32–). These DIC species are pH-dependent, playing a significant role in the selective removal of fluoride by the CDI process. Thus, there is a knowledge gap in understanding the effects of membranes in membrane capacitive deionization (MCDI) on fluoride removal. In this study, we examined the key operating parameters in CDI and MCDI, including applied constant voltages and different types of anion-exchange membranes (AEMs), on the desalination performance in F- and dissolved inorganic carbon water matrices. The application of AEMs significantly improved the salt adsorption capacity (SAC) for both F- and DIC species, and reduced energy consumption. However, it simultaneously resulted in a notable decrease in F- selectivity as membranes control mass transfer. Higher applied voltages enhance the SAC performance for F- and DIC species, but also induce more severe Faradaic reactions, leading to increased energy consumption and lower energy efficiency. Additionally, ion species and pH changes during CDI and MCDI processes are interrelated, indicating that stability tests of CDI electrodes in batch mode are not reliable when using the same testing solution repeatedly. The diverse valence states of ions in the solution impact pH variations under different voltages in the CDI/MCDI process. These findings provide valuable insights into the development of water purification and desalination technology, particularly for the application and further advancement of selective fluoride removal by the CDI process.

Porous N, P co-doping Ti3C2Tx MXene for high-performance capacitive deionization

The emerging energy-saving and environmentally friendly capacitive deionization (CDI) technology has attracted more and more attention. However, it remains a great challenge to develop CDI electrode materials with excellent comprehensive properties. Herein, the porous N, P co-doping Ti3C2Tx MXene (N, P-Ti3C2Tx) was prepared successfully by combining simple flocculation with an annealing process. Benefitting from the synergistic effect of the combination of porous structure and co-doping of N and P heteroatoms, the N, P-Ti3C2Tx exhibits substantial specific surface area, which provides more surface bounding active sites for electrochemical reactions, thus assisting to boost the CDI performance. As a result, the N, P-Ti3C2Tx exhibited an admirable salt (Na+) adsorption capacity of 53.3 mg g−1 and exceptional recycling property. Impressively, the N, P-Ti3C2Tx also exhibited superior desalination performance of Pb2+, characterized by an exceptionally high desalination capacity of up to 168.2 mg g−1 at 1.2 V, and the corresponding desalination rate reached 0.047 mg g−1 s−1. Additionally, the deionization mechanism involved was elucidated through a series of characterizations. This work will furnish an effective avenue for the innovative design of MXene-based electrode materials toward high-performance CDI.

Capacitive deionization exploiting La-based LDH composite electrode toward energy efficient and selective removal of phosphate

Capacitive deionization (CDI) is a promising technology for removing phosphate from wastewater. Its practical implementation is however hindered by the constraints on the electrode materials. To boost the adsorption capacity, phosphate selectivity, and cost-effectiveness of the electrode, this study proposed a composite electrode blending Lanthanum-based layered double hydroxide (CaLa LDH) and activated carbon (AC). It capitalizes on the synergistic effects of electric double layer capacitance (EDLC) of AC and the diffusion-controlled charge storage (pseudocapacitive behavior) of CaLa LDH. By optimizing the mass ratios of the constituents and the electrode material loading capacities, the composite electrode AC/Ca-La LDH-5020 was developed, which contains 20 mg of 50 wt% CaLa LDH. This composition achieved a remarkable phosphate adsorption capacity of 34.8 mg P /g and a low energy consumption of 0.0051 kWh/g P in constant voltage (CV) mode. It represented a 241 % increase in adsorption capacity (mg P/g) and 71 % decrease in specific energy consumption (kWh/g P) compared to the electrode made solely of AC. Particularly the moderate inclusion of Lanthanum contributes to its cost-effectiveness. Moreover, further studies extensively examined the impacts of electrical driving force, including applied voltage in constant current (CC) mode and applied current in constant voltage (CV) mode, on the phosphate removal efficiency. The composite electrode remained stable performance with the presence of the high content of coexisting anions (e.g.，Cl−，SO42−, HCO3−, NO3−), obtaining high selectivity coefficient of phosphate over other anions. This study highlighted the practical potential of AC/Ca-La LDH composite electrode for advancing CDI technology for phosphate removal in an efficient, energy-saving and cost-effective manner.

Enhanced construction of 3D carbon skeleton through molten salt coupling activation effect for high efficiency capacitive deionization of lead (II) ions removal in wastewater

Efficiently eliminating of highly toxic ultra-dilute lead ions (Pb2+) from wastewater is a challenging task. Capacitive deionization (CDI) technology, based on the electrochemical capacitance mechanism, has emerged as a pivotal approach to address this challenge. In this work, a KNO3-mediated molten salt-coupled activation strategy was proposed to prepare nitrogen-doped hierarchical porous biomass carbon electrode material (3DCF-650-0.2) with a three-dimensional carbon skeleton, which was integrated into a symmetrical CDI device for Pb2+ removal. The 3DCF-650-0.2 electrode exhibited a high specific capacitance of 330.3 F g-1 at a current density of 1 A g-1, with a capacity retention rate of 98.45% after 10,000 cycles at 10 A g-1. Furthermore, the electrochemical adsorption capacity of the CDI device for Pb2+ reached 72.86 mg g-1 (1.2 V, 50 mg L-1), and the CDI device retained a high adsorption capacity of 91.14% after twenty adsorption/desorption cycles. These excellent adsorption properties are attributed to the in-situ activation and gas foaming of KNO3, which favors the production of reasonable pore structure (electric double-layer capacitance) and an appropriate pyrrolic nitrogen doping amount (selective adsorption) in the carbon materials. This work provides insight into the mechanism of the molten salt-coupled activation strategy, offering new ideas for the targeted design of high-performance CDI biomass carbon materials.

Effects of electrode/electrolyte materials on heavy-metal removal in industrial wastewater with flow capacitive deionization method

The expansion of industrial facilities poses a significant environmental risk due to the generation of extensive wastewater containing complex components that effluent human health. Flow-electrode Capacitive Deionization (FCDI) technology has emerged as a promising solution for wastewater treatment due to its unlimited adsorption capacity and continuous long-term operations compared to conventional systems. This study investigates the efficiency of the FCDI system in purifying industrial wastewater by extracting complex heavy metal ions, intending to achieve complete recycling and zero discharge. Different electrolyte/electrode materials were investigated to achieve high removal efficiency, including electrolytes such as sodium chloride (NaCl) and sodium sulfate (Na2SO4), and electrodes such as active carbon (AC) and C65 carbon black (C65 CB) used in lithium-ion batteries. We found that the innovative combination of Na2SO4 electrolyte with 0.1 g of C65 CB exhibited an exceptional salt removal efficiency of 90 %, surpassing NaCl electrolyte which showed 68 % efficiency. Additionally, we observed higher adsorption with C65 CB slurry compared to AC when using Na2SO4 electrolyte. To deepen our insights, Molecular Dynamics (MD) simulations were conducted to explore heavy metal ions interactions with electrode/electrolyte and membrane materials under an electric field. The results indicated that Ni2+ ions had the highest passage rate of 80 % across the membrane, followed by Cr2+, Cu2+, and Zn2+. Furthermore, superior adsorption of Ni2+ ions onto the C65 CB electrode was noted, contributing to enhanced charge transfer and overall conductivity. Furthermore, we evaluated the economic and environmental implications associated with implementing the FCDI system in practical. This study presents a novel approach by using C65 carbon black (CB) with Na2SO4 as the electrolyte, indicating high adsorption efficiency at low carbon loading electrode. This combination offers a cost-effective and sustainable solution for improving complex heavy metal ion removal in FCDI systems. Overall, our study’s findings significantly contribute to offering crucial insights into optimizing FCDI technology for efficient heavy metal ions removal in industrial wastewater treatment using lithium-ion battery anode/cathode electrode material.

Flow-electrode capacitive separation of organic acid products and recovery of alkali cations after acidic CO2 electrolysis

Acidic CO2 electrolysis, enhanced by the introduction of alkali cations, presents a strategic approach for improving carbon efficiency compared to processes conducted in neutral and alkaline environments. However, a significant challenge arises from the dissolution of both organic acids and alkali cations in a strongly acidic feed stream, resulting in a considerable energy penalty for downstream separation. In this study, we investigate the feasibility of using flow-electrode capacitive deionization (FCDI) technology to separate organic acids and recover alkali cations from a strongly acidic feed stream (pH ~ 1). We show that organic acids, such as formic acid and acetic acid, are retained in molecular form in the separation chamber, achieving a rejection rate of over 90% under all conditions. Alkali cations, such as K+ and Cs+, migrate to the cathode chamber in ionic form, with their removal and recovery significantly influenced by their concentration and the pH of the feed stream, but responding differently to the types and concentrations of organic acids. The energy consumption for the removal and recovery of K+ is 4 to 8 times higher than for Cs+, and the charge efficiency is significantly influenced by the types of organic acid products and alkali cations. We conduct a series of electrochemical measurements and analyze the impedance spectroscopy, identifying that hindered mass transfer governed the electrode process. Our findings underscore the potential of FCDI as an advanced downstream separation technology for acidic electrocatalysis processes.

Flexible beads-on-string hierarchically porous carbon nanofiber/nanotube composites for enhanced capacitive deionization performance in water desalination

Capacitive deionization (CDI) has garnered significant interest for desalinating water and wastewater. However, electrode materials have remained a primary constraint in CDI technology. This study incorporated carbon nanotubes (CNTs) into a polyacrylonitrile (PAN) solution to synthesize a hierarchically porous activated carbon nanofiber (ACNF)/CNT composite. The ACNF/CNT composite possesses a highly flexible structure characterized by a distinctive beads-on-string morphology. It exhibits a specific surface area of 699 m2/g, a specific pore volume of 0.448 cm3/g, and an average pore width of 3.38 nm. The composite is composed of micropores (38 %), mesopores (59 %), and macropores, creating a multi-scale porous architecture. The surface capacitance of the ACNF/CNT composite is six times greater than that of the ACNF alone, and its charge transfer resistance is reduced to one-tenth. Furthermore, the electrosorption capacity of the ACNF/CNT composite as CDI electrodes was found to be 17.3 mg/g for a 500 mg/L NaCl solution, demonstrating stability over 30 cycles. Kinetic studies suggest that the mesopore-rich beads-on-string structure enhances intraparticle diffusion and the electrosorption process. The ACNF/CNT composite also demonstrates exceptional flexibility and mechanical stability, which are crucial for its application at a pilot scale. This study introduces a novel hierarchically porous electrode material for CDI desalination.

Green self-templated synthesis of P-doped mesoporous carbon from dual sodium salts with improved average pore size for capacitive deionization

Mesoporous carbon materials hold significant potential in capacitive deionization (CDI) technology owing to expansive accessible surface area, more adaptable pore structure, excellent conductivity properties and effective surface modification and functionalization. While templating is a common method for synthesizing mesoporous carbons, the commonly used hard and soft templating approaches among them suffer from the challenges of expensive precursors and templating agents, complex procedures, secondary contaminants and difficulties in template removal. In contrast, the self-templating method not only circumvents the traditional template removal or combustion steps but also eliminates the use of organic solvents and hazardous chemicals, thus minimizing environmental impact. In this paper, we have successfully synthesized phosphorus-doped mesoporous carbon with a large average pore size (paver) using a green and convenient self-templating method employing dual sodium salts of sodium alginate (SA) and sodium phytate (SP). Compared to single SA (6.76 nm) or SP (3.74 nm) self-templated carbonization, the average pore size of carbon materials obtained from dual self-templated carbonization with a proportional mixture (12.97 nm) is significantly improved. The larger average pore size provides a greater surface area for electrode-electrolyte interactions, allowing for easier access and faster diffusion of ions into the pores, thereby enhancing the electrochemical and capacitive deionization properties of the material. The resulting material demonstrates promising electrochemical and desalination performance as evidenced by possessing a specific capacitance of 175.8 A/g and an adsorption capacity of 19.65 mg/g, underlining its potential for application in capacitive deionization utilizing mesoporous carbon materials with large average pore size.

Simultaneous desalination and removal of organic pollutants in a novel bifunctional FCDI system: The enhancement by in-situ reutilization of chloride ions

A new system of flow electrode capacitive deionization coupled with in situ electro-oxidation (FCDI-EO) was constructed to achieve the degradation of organic pollutants while maintaining high desalination efficiency. The effects of different parameters of potential difference, electrolyte, and pH on the chloride removal performance of FCDI-EO and the removal performance of rhodamine B (RhB) were investigated. Under the optimal conditions of potential difference = 4 V, [Cl−] = 500 mg/L, and pH = 4, the removal of chloride ions, RhB and total organic carbon (TOC) was as high as 88.74 %, 99.02 %, and 87.82 %, respectively. The quenching experiments showed that hydroxyl radicals (OH) and reactive chlorine species (RCS) were involved in the FCDI-EO system. The liquid chromatography-mass spectrometry (LC-MS) analysis suggested the possible mineralization pathway of RhB. Furthermore, toxicity assessment analysis showed that the toxicity of the degradation intermediates of RhB decreased during the treatment. Overall, this study provides a promising process that reducing the generation of high-concentration saline water in desalination and in situ utilizing the Cl− gathered from the feed water. The findings of this study could provide useful guidance for the development of flow electrode capacitive deionization technology and organic pollutant control.

Dual redox centers in MnCo2O4 nanorod cathode for highly efficient capacitive deionization

Capacitive deionization (CDI) technology via faradic electrodes with active redox pairs has achieved tremendous success in desalination. However, the inner collaborative mechanisms of multi-redox centers in electrodes are rarely deep-analyzed. Thus, this work intensively investigated the inner enhanced mechanisms of multi-redox centers, starting from the dual-redox-based MnCo2O4 nanorod (MCO-NR) cathode in capacitive desalination. The electrochemical tests indicated a surface capacitive ratio of MCO-NR as high as 86 % when the scan rate was 100 mV s−1. Multi-dimensional CDI tests demonstrated that the highest capacity of MCO-NR could reach 61.78 mg g−1, with four theory models elaborating the electrosorption kinetics and maximum desalination capability. The refined ex-situ XPS measurements, carefully designed comparative experiments, and DFT calculations were used to analyze the Na+ (de)intercalation characteristics, the inner enhanced electrosorption mechanisms of dual redox centers, and the effects that the Mn redox center exerts on the MnCo2O4 structure. These results showed the superiority of dual- or multi-redox-center-based faradic capacitive desalination, providing a new perspective for designing high-property faradic electrode materials.

Selective adsorption of divalent and trivalent cations in porous electrodes.

The capacitive deionization technology uses the electrochemical adsorption of ions in porous electrodes to desalinate seawater or brackish water. Recently, capacitive deionization has gained significant attention as a technology for selective adsorption of ionic species from multicomponent aqueous electrolytes. To investigate the mechanism of selective adsorption at the molecular level, we performed molecular dynamics simulations of aqueous electrolytes and porous electrodes with different divalent or trivalent ions, electrode pore sizes, and applied voltages. We calculated the free energy barriers preventing ions from entering the pores of the electrode and the structure of the water molecules near the ions and the electrode surface under various conditions. Our results suggest that, when the pore and ion sizes are comparable, the steric and electrostatic interactions between the hydrated ions and electrode pores are comparable in magnitude. Moreover, the relative importance of the two interactions can be reversed by slight changes in the external conditions, such as the ion size, valence of the ions, electrode pore size, and applied voltage. Thus, by finely tuning the electrode pore size and the applied voltage, it may be possible to selectively adsorb a particular ionic species from a multicomponent electrolyte through capacitive deionization using a porous electrode.

Investigation of the Deionization Rate of Asymmetric Capacitive Deionization Technology for the Treatment of Short-Chain Perfluoroalkyl Substances (PFAS)

Objectives : This study aims to introduce and evaluate the effectiveness of asymmetric membrane capacitive deionization (ACDI) in removing short-chain perfluoroalkyl substances (PFAS), specifically perfluorobutane sulfonic acid (PFBS), from aqueous solutions. This study offers important insights for the advancement of CDI technology in the sustainable treatment of industrial wastewater containing PFAS.Methods : ACDI was employed by removing the anion exchange membrane from conventional membrane capacitive deionization system. The effect of key operational parameters such as voltage (0.5~1.2 V), initial concentration (50~500 mg/L), and flow rate (1~5 ml/min) on PFBS removal efficiency was systematically investigated. Additionally, PFBS removal performance in the presence of chloride ions was also investigated to determine competing ion effects.Results and Discussion : The ACDI system significantly outperformed both CDI and MCDI, achieving a maximum deionization rate of 0.032 mg/g/s, compared to 0.012 mg/g/s for CDI and 0.01 mg/g/s for MCDI. Increasing the applied voltage from 0.5 V to 1.2 V enhanced the deionization rate, with the highest rate observed at 1.2 V. Higher initial PFBS concentrations also improved the deionization rate, increasing from 0.0009 mg/g/s at 50 mg/L to 0.032 mg/g/s at 500 mg/L. The optimal flow rate was found to be 2 ml/min, balancing ion contact time and throughput, resulting in the highest deionization rate. The presence of competing ions, such as chloride, reduced PFBS removal efficiency, as shown by the decrease in deionization rate when NaCl was added to the feed solution.Conclusion : Overall, the ACDI system demonstrated superior deionization capacity and energy efficiency for PFBS removal, highlighting its potential as a sustainable and efficient technology for treating water contaminated with short-chain PFAS. Future research should address the challenges posed by competing ions in real-world wastewater to further optimize the ACDI system’s performance.

Heavy metal removal performance of capacitive deionization technology studied by machine learning

Capacitive deionization (CDI) technology is utilized for efficient treatment of industrial wastewater, characterized by low energy consumption and environmental protection. In order to comprehend the correlation between key experimental parameters and the electrosorption capacity (EC) of heavy metals in CDI technology, this paper employs a genetic algorithm (GA) to optimize a backpropagation artificial neural network (BPANN) for predicting the EC of CDI technology for heavy metal ions, with the characteristics of electrode materials converted into numerical characteristics for further analysis. Compared to the BPANN, the optimized GABPANN model demonstrates superior predictive accuracy. It achieves automatic adjustment of the hidden layer structure, neuron count, and transfer functions. Furthermore, the grey relational analysis indicates that the electrode material and the initial pH value of the solution are pivotal in determining the EC of heavy metal ions. This underscores the efficacy of machine learning (ML) algorithms in forecasting the nonlinear dynamics of CDI systems and elucidates the influence of individual parameters on the efficacy of heavy metal removal.

Commercialization Efforts of Capacitive Deionization Technology in Water Treatment Processes

AbstractAlthough capacitive deionization (CDI) technology has been studied intensively for more than 20 years, its commercialization remains in the initial stage, which is partly caused by the insufficient knowledge exchange between academia and industry. This concept reviews multiple scaling‐up efforts in the CDI technology for treating real water streams, following a case‐by‐case fashion. While the cell architecture in pilot scales is limited to the membrane CDI, highlighting the necessary role of ion‐exchange components during scaling‐ups, different ways of electrode stacking, i. e., monopolar and bipolar, are available. The performance indicators of these CDI systems when treating real water streams are summarized to gain insights into industrial practices. Importantly, key discrepancies in cell components and performances between pilot‐scale and lab‐scale studies are emphasized. The main challenges in large‐scale CDI systems for industrial purposes are discussed, providing hints for a better integration of research and applications.

Carbon-modified bentonite ion-exchange electrode in rocking-chair capacitive deionization with superior desalination capacity and high stability

Conventional carbon electrodes possess low desalination capacity and poor cycling stability, while faraday electrode materials are not economical with limited resource for capacitive deionization (CDI) technology. Therefore, exploring new type of electrode materials with high desalination capacity, low cost and excellent cycle stability is highly desirable. Bentonite (Bent) is an excellent ion-exchange material, with high natural abundance, super stability, but it has low conductivity. In this paper, a nitrogen-doped carbon modified Bent (NC@Bent) was prepared by in-situ polymerization of dopamine on the surface of Bent followed by carbonization. The N,C-modified thin layer on Bent improved the conductivity, boosting the charge transportation and ion diffusion. The NC@Bent was used as ion-adsorption electrode, exhibiting excellent electro-adsorption behavior. In a rocking-chair CDI (RCDI) cell, it delivered an extraordinary desalination capacity of 82 mg g−1 and super cycling stability with 90 % capacity retention in 50 cycles. Finally, the total dissolved salts in the actual groundwater were effectively reduced by using the current RCDI cell, meeting the WHO recommendation for drinking water. In consideration of the unique feature of low-cost and non-toxicity of Bent, this ion-exchange electrode material (NC@Bent) has much potential for drinking-water purification.

Techno-economic analysis of capacitive deionization technology: An overview and case studies in Vietnam

Techno-economic analysis of capacitive deionization technology: An overview and case studies in Vietnam

Multifunctional capacitive deionization removal of metal ions via crumpled phosphorus-doped Ti3C2Tx MXene nanosheets

Capacitive deionization (CDI) technology shows excellent development prospects in seawater desalination and the removal of heavy metal ions from wastewater due to its high efficiency, environmental protection, and energy saving. However, the lack of suitable electrode materials with excellent performance limits the development of CDI. Herein, a crumpled phosphorus-doped Ti3C2Tx MXene nanosheets (P-Ti3C2Tx) was synthesized by an in-situ phosphating strategy. The P heteroatom doping not only improves the electrical conductivity and modulates the surface properties of Ti3C2Tx MXene nanosheets, but also availably alleviates the self-stacking problem of Ti3C2Tx MXene nanosheets. Specifically, the P-Ti3C2Tx shows excellent multifunctional removal performance for various metal ions (Na+: 61.8 mg g−1, Pb2+: 84.3 mg g−1, and Cr3+: 99.7 mg g−1). Additionally, the removal mechanism of P-Ti3C2Tx is investigated by systematic characterizations and theory calculations. Therefore, this work provides new ideas for the development of multifunctional CDI electrode materials with excellent performance.

Machine Learning-Guided Prediction of Desalination Capacity and Rate of Porous Carbons for Capacitive Deionization.

Nowadays, capacitive deionization (CDI) has emerged as a prominent technology in the desalination field, typically utilizing porous carbons as electrodes. However, the precise significance of electrode properties and operational conditions in shaping desalination performance remains blurry, necessitating numerous time-consuming and resource-intensive CDI experiments. Machine learning (ML) presents an emerging solution, offering the prospect of predicting CDI performance with minimal investment in electrode material synthesis and testing. Herein, four ML models are used for predicting the CDI performance of porous carbons. Among them, the gradient boosting model delivers the best performance on test set with low root mean square error values of 2.13mg g-1 and 0.073mg g-1 min-1 for predicting desalination capacity and rate, respectively. Furthermore, SHapley Additive exPlanations is introduced to analyze the significance of electrode properties and operational conditions. It highlights that electrolyte concentration and specific surface area exert a substantially more influential role in determining desalination performance compared to other features. Ultimately, experimental validation employing metal-organic frameworks-derived porous carbons and biomass-derived porous carbons as CDI electrodes is conducted to affirm the prediction accuracy of ML models. This study pioneers ML techniques for predicting CDI performance, offering a compelling strategy for advancing CDI technology.

Selective capacitive removal of Pb(II) ions from industrial wastewater using NF/Mn2CoO4@MoO2 electrodes

To achieve targeted removal of Pb2+ from industrial wastewater, a NF/Mn2CoO4@MoO2 composite electrode, synthesised using the hydrothermal method combined with electrodeposition technology, was employed to construct an asymmetric capacitive deionization (CDI) system to selectively electro-adsorb and desorb Pb2+ ions. The electrode exhibited pseudocapacitive characteristics in solutions containing Pb2+, facilitating rapid and reversible redox reactions. The asymmetric CDI system, utilising graphite paper as the positive electrode and NF/Mn2CoO4@MoO2 as the negative electrode, displayed exceptional adsorption performance at 1.4 V for 1 h, decreasing the Pb2+ concentration from 50 ppm to 4 ppb, achieving an adsorption capacity of 156.24 mg g−1, and displaying outstanding cyclic stability. Moreover, the electrode demonstrated preferential adsorption of Pb2+ in mixed solutions containing multiple heavy metal ions, with relative removal coefficients of 4.48 − 19.86 compared with other ions. Analysis of the adsorption mechanism indicated that during the adsorption process, Pb2+ was embedded between MoO2 layers, disrupting the electron cloud symmetry and triggering an oxidation reaction. Octahedral MoO2 then lost electrons and transformed into tetrahedral [MoO4]2-, forming PbMoO4 with embedded Pb2+ between the layers, and achieving effective removal of Pb2+ with high selectivity. Molecular dynamics simulations and density functional theory (DFT) calculations confirmed the high selectivity of the prepared electrode for Pb2+ ions based on stronger binding of Pb2+ to MoO2 than other ions. The electrode has application potential for the capacitive removal of Pb2+ from industrial effluent through CDI technology.

Enabling High Capacity and Stable Sodium Capture in Simulated Saltwater by Highly Crystalline Prussian Blue Analogues Cathode

Prussian blue analogues (PBAs) are considered as promising cathode materials for capacitive deionization (CDI) technology due to their 3D open‐frame structure and tunable redox active sites. However, the inevitably high content of [Fe(CN)6] vacancies in the crystal structure results in a low salt adsorption capacity (SAC) and poor recycling performance. Herein, a high‐salt nano‐reaction system is established by mechanochemical ball milling, enabling the preparation of a variety of highly crystallized PBAs (metal hexacyanoferrate, MHCF‐B‐170, M = Ni, Co, or Cu) with low vacancies (0.05–0.06 per formula unit). The reduction of vacancies in the PBAs lattice not only strengthens the conductivity and promotes the rapid transfer of electrons, but also reduces the migration energy barrier and accelerates the fast and reversible diffusion of Na+ ions. The structural characterization method and theoretical simulation demonstrates the excellent reversibility and crystal structure stability of MHCF‐B‐170 during the CDI process. Impressively, the NiHCF‐B‐170 exhibits excellent CDI performance, characterized by an exceptionally high SAC of up to 101.4 mg g−1 at 1.2 V, and demonstrates remarkable cycle stability with no significant degradation observed even after 100 cycles. This PBAs with low Fe(CN)6 vacancies are expected to be a competitive candidate material for CDI electrodes.