Capacitive Deionization Technology Research Articles

Fast and stable lithium extraction enabled by less-defective graphene supported LiMn2O4 conductive networks in hybrid capacitive deionization

Hybrid capacitive deionization (HCDI) technology for lithium (Li+) extraction from brine has received growing concern owing to its easy operation, low energy consumption, and environmental friendliness. LiMn2O4 (LMO) as an affordable Li+ extraction material offers a high theoretical capacity, while the slow ion insertion kinetics and unavoidable Mn dissolution restrict its wide usage. Herein, an LMO-based electrode supported by less-defective (inherent lattice defects and oxygen-containing defects), interconnected graphene conductive networks is proposed for fast and stable Li+ extraction from brine using HCDI. The rGO/LMO electrode displays an excellent conductivity of 0.42 S·cm−1 and a high specific capacitance of 418.26 F·g−1. In the HCDI system, the rGO/LMO electrode delivers a Li+ adsorption capacity up to 4.34 mmol·g−1 with a rapid adsorption rate of 0.33 mmol·g−1·min−1 (0.05 mol·L–1 LiCl, 1.0 V), demonstrating both of the outstanding adsorption capacity and rate abilities as defined by Ragone plots. In a solution with a high Mg2+/Li+ molar ratio of 20, the separation factor can reach 71.32. By employing rGO/LMO electrode to simulated Atacama brine, the separation factor of Li+ from Na+, K+, Ca2+, and Mg2+ are calculated to be 473.89, 74.86, 63.07, and 38.55. Particularly, the rGO/LMO electrode shows remarkable cycling stability with a capacity retention rate of 90.73 % (50 cycles). This developed less-defective graphene-wrapped LMO electrode holds significant importance in enhancing selective Li+ extraction performance with fast rate and stability.

Enhanced removal of copper ions from wastewater using small spherical Fe-N-C material via selective electro-sorption: Experiment and calculation

In the current research, the resource recovery technology for Cu-containing wastewater from electroplating is still a difficult problem. Capacitive deionization technology (CDI) has received widespread attention for its strengths of convenient operation, low cost, and environmentally friendly. In this paper, Fe-N-C was prepared as the electrode material for the treatment of Cu-containing wastewater by capacitive deionization technology through one-pot thermal method. The optimum treatment conditions of Fe-N-C for Cu-containing wastewater were voltage equal to 1 V, pH = 5, and the inlet flow rate was 5 mL/min. The electro-adsorption capacity of a single Cu-containing solution of 400 mg/L could reach 389.4 mg/g. Meanwhile, by carrying out ion competition experiments on five cations, namely Zn2+, Na+, Mg2+, K+, and Cu2+, which demonstrated Fe-N-C had a significant selectivity for the electro-adsorption removal of Cu2+. Theoretical calculations revealed that Fe3N and Fe4N were more dominant for Cu2+ adsorption energy and more binding for competing ions in the monovalent state, but had less practical effect on Cu2+ adsorption. The morphology of the Fe-N-C was analyzed in more depth by X-ray photoelectron spectroscopy (XPS) and other characterization methods. Combined with density functional calculations, Cu would not only displace with Fe in FeXN to form a more stable CuXN structure, but also combine with FeXN to form a Cu-FeXN structure. This is conducive to accelerating the application of CDI to recover Cu2+ from heavy metal wastewater.

Application of capacitive deionization technology in water treatment and coupling technology: a review

CDI plays an important role in water desalination, water softening, removal of heavy metals, purification of industrial wastewater, and removal of nutrients, and CDI coupling technology is emphasized.

Simultaneous removal of tetracycline and copper ions from wastewater by flow-electrode capacitive deionization

ABSTRACT To effectively solve the problem of tetracycline (TC) and Cu2+ contamination in wastewater, this study innovatively proposed a low-energy flow-electrode capacitive deionization (FCDI) technology to simultaneously remove TC and Cu2+ from wastewater. The removal efficiencies of TC and Cu2+ using FCDI was investigated under various voltages, electrode flow rates, influent flow rates, and electrode liquid concentrations. The results showed that the removal efficiency of TC and Cu2+ was 60.78% and 84.43%, respectively. The energy consumption for TC and Cu2+ removal was only 1.76 and 1.10 kWh kg−1, which was lower than other electrochemical systems. The ion removal performance of the FCDI system remained stable after six cycles of continuous operation. These findings demonstrated the promising potential of FCDI as an innovative technology for the simultaneous removal of TC and Cu2+, presenting a significant prospects for application in the water treatment field.

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

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

Synthesis of black TiO2 nanotubes decorated biomass-derived spongy carbon as an electrode material for producing deionized water through capacitive deionization technology

The capacitive deionization (CDI) technique is considered a promising eco-friendly desalination method due to its high energy efficiency, ease of operation, and simplistic electrode regeneration capability. Thus, significant research is focused on developing highly efficient electrode materials with high electrochemical stability and salt electro-adsorption capacity (Sc) behavior during operation because these are the governing factors in examining the measured activity of fabricated CDI cells. In this manuscript, we report the synthesis of hydrogenated titanium nanotubes@spongy activated carbon (HTiO2 NTs@SAC) using pyrolysis and hydrothermal processes. The SAC is synthesized by the pyrolysis of spongy loofa in an inert atmosphere and further hydrothermally activating it in an aqueous potassium hydroxide solution. The hydrothermal process activates and enhances the hydrophilicity of SAC. HTiO2 is synthesized electrochemically at 20 V in 0.1 M perchloric acid. Such HTiO2 NTs@SAC configuration can provide excellent pathways to increase ion adsorption and improve the kinetics of charge transfer by enhancing the contact between the electrolyte and electrode at the interface. It is found that HTiO2 NTs@SAC has a specific capacitance (Cs) of 385.7 F g−1 compared with 332.7 F g−1 for SAC. The salt electrosorption capacity (Sc) of HTiO2 NTs@SAC electrode material is found to be 24.90 mg g−1 in 250 μS cm−1 saline solution at 1.2 V, which is much higher than the values obtained for SAC (9.8 mg g−1). HTiO2 NTs@SAC has also shown an antimicrobial effect toward gram-negative bacteria and exhibited good performance in the supercapacitor application, wherein HTiO2 NTs@SAC showed a higher Cs (505.55 F g−1) than SAC (380 F g−1) at 1 A g−1. Thus, we demonstrate that the prepared composite can be used as an energy storage material, an antibacterial material, and a CDI electrode in the CDI technology.

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.

Rectorite in flow-electrode capacitive deionization with three-dimensional current collector to achieve cost-effective desalination

The innovative design of collector is a top priority to drive the advancement of flow electrode capacitive deionization (FCDI) technology. Currently, the majority of FCDI research has concentrated on the implementation and modification of carbon-based flow electrode materials, while ignoring the effect of the current collector in FCDI. In this study, a 3D-FCDI configuration with porous titanium foam as the collector is designed, and rectorite (Rec) is used as the flow electrode in 3D-FCDI. Thanks to the porous structure of the 3D current collector, the collision opportunities of electrons with the Rec particles are increased and the long-distance migration of electrons in the conventional graphite collector is overcome, thus improving the system conductivity. The Rec exhibits good electrode dispersion, desalination rate, and energy consumption at low cost. In addition, the ASAR of Rec can be achieved by adjusting the electrode concentration (5 wt%), electrode flow rate (25 mL min−1) and operating voltage (1.8 V) to 11.43 μg cm−2 min−1. This study demonstrates the capability of 3D-FCDI configuration to advance the creation and implementation of FCDI.

Electric double layer capacitive adsorption and faradaic pseudo-capacitance behavior of ZnFe-PANI/CNT electrode for phosphate removal in capacitive deionization

Capacitive deionization technology possesses puissant competitiveness in the field of water treatment due to its low cost and high efficiency. In this study, polyaniline (PANI) doped and carboxyl intercalated metal hydroxide composite (ZnFe-PANI/CNT) was developed by a simple co-precipitation method, and used as anode electrode for phosphate removal in sewage. The results show that ZnFe-PANI/CNT electrode can efficiently remove phosphate at concentration of 2–10 mg/L at a wide range of pH (3–10) by electric double layer capacitive adsorption and pseudocapacitive adsorption. The concentration of phosphate in the effluent was as low as 0.095 mg/L, and the coexisting anions (Cl−, NO3−, SO42− and HCO3−) hardly inhibited the phosphate adsorption by ZnFe-PANI/CNT composite electrode. In addition, under the optimal phosphate adsorption conditions (pH = 7 and applied voltage of 1.2 V), the energy consumption of CDI system was calculated as low as 0.00274 kWh/g P and 0.017 kWh/m3 water, realizing the expectation of low cost and high efficiency operation.

Recent advances in the fixed-electrode capacitive deionization (CDI): Innovations in electrode materials and applications

Conventional capacitive deionization (CDI), originally developed as a promising desalination technique based on the formation of electric double layers (EDLs) at the surface of porous electrodes, has recently shown significant advancements. Notably, the utilization of pseudocapacitive electrodes has demonstrated the capability to enhance salt adsorption capacity (SAC) and selectivity of specific ions. This comprehensive review encapsulates the latest research endeavored in CDI, with an emphasis on electrode materials and their role in augmenting SAC. The development of electrode materials has broadened the scope of CDI applications on the water and wastewater treatment and resource recovery. Hence, we also evaluated the manifold applications of CDI, including resource recovery (e.g., lithium, phosphate and nitrate), anion removal (e.g., fluoride, sulfate, chromium and arsenic), water softening, and the removal of heavy metals (e.g., nickel, cesium, lead, copper, cadmium and chromium) in addition to the water desalination. Lastly, we provide a forward-looking perspective on forthcoming research directions and potential developments within the realm of CDI technology.

Implementation of fungal-based desalination through capacitive deionization for urban water provision: a conceptual framework

The increasing demand for clean water in urban areas calls for innovative and sustainable water treatment solutions. Capacitive deionization (CDI), using fungal-based materials for desalination, offers potential benefits such as sustainability, low cost, and scalability, for urban water provision. However, few studies have explored the practical application of fungal-based CDI technology. This research assesses the feasibility of implementing fungal-based CDI technology in urban water provision systems, drawing on the key study from Chen et al.’s 2022 research, examining the preparation and performance of fungal-based CDI electrodes derived from Aspergillus niger. To create a reliable and up-to-date conceptual model, additional literature from indexed journals, focusing on CDI in desalination facilities from the past decade, is also reviewed. A conceptual framework was developed to demonstrate the potential integration of fungal-based CDI technology into urban water treatment systems, and taking into account factors such as capital and operational costs, scalability, and sustainability. The outcome of this study is a conceptual model that promotes further development of urban water provision through desalination, broadening the perspective on the application of emerging biotechnology, using fungal-based materials for water provision.

Selective removal of Cs+ and Sr2+ by electrosorption using intercalating titanosilicate

The utilization of ion intercalate capacitive deionization technology is garnering attention as an electrified water treatment method. This study proposes a capacitive deionization technology incorporating Dual-cation TitanoSilicate (DTS) to enable efficient electro-sorption/desorption of radioactive ions Cs and Sr. The synthesized DTS possesses a robust structure, high selectivity for Cs and Sr, and substantial adsorption capacity, incorporating redox-active titanium. Employing DTS as an active material in the electrode demonstrated a high adsorption capacity (186 mg Cs/g, 177 mg Sr/g) and rapid adsorption kinetics, reaching maximum capacity within 30 min, even in environments with a tenfold excess of competing ions. Furthermore, our system exhibited stable performance over 5 cycles of adsorption/desorption, and post-desorption analyses confirmed the durable structure stability without significant alterations. This study highlights the feasibility of CDI technology utilizing DTS for cesium and strontium removal.

Electrosorption of uranium (VI) by sulfonic acid‑decorated FeOOH nanorods

The capacitive deionization (CDI) technology for the removal of U(VI) has been the focus of attention because of its superiorities in operation cost, energy consumption, and environmental friendliness. In this report, electrode materials based on sulfonic acid‑decorated FeOOH were applied to CDI and flow electrode capacitive deionization (FCDI) for the first time. The sulfonic acid‑decorated FeOOH nanorods presented a high electrosorption capability of U(VI) in the CDI system (709.4 mg g−1 at 1.2 V and pH = 4.0, based on Langmuir model), which may result from the coordinative surfaces as well as the mesoporous structures of FeOOH. The thermodynamic and kinetic behaviors of the electrosorption process can be well-fitted using the Freundlich and pseudo-second-order model. The effective electrosorption in the presence of Na+ competitive ions and recycling of adsorbents in the CDI system further demonstrated the potential application of sulfonic acid‑decorated FeOOH nanorods for the electrosorptive removal of U(VI) from radioactive wastewater. The electrosorption mechanism was determined to be a combined process that is composed of diffusion of the uranyl ions into the EDL and adsorption onto the surface of FeOOH via the coordination interaction from Fe-OH and sulfonic acid groups (-SO3H). Further, continuous FCDI batch experiments in low concentration of feed water (60 mg L− 1 U) show that removal efficiency of U remained over 99% in 10 times continuous cycles, endowing it more possibilities for capacitive deionization from research to practical application.

Activation-self-activation craft for one-step synthesis of GO-inbuilt mesopore-dominated N-doped hierarchical porous carbon in capacitive deionization capture of Ni(II)

Capacitive deionization (CDI) is considered a polar-promising technology to remove heavy-metal ions from wastewater. Herein, a green activation-self-activation strategy was exploited to build graphene (GO)-inbuilt mesopore-dominated N-doped hierarchical porous carbons (ENHPCs) using sodium lignosulfonate (SLS) as carbon sources/self-activators. Different from SLS self-activation and K2C2O4-SLS activation-self-activation, ENHPCLKG gained via GO-mediated K2C2O4-SLS activation-self-activation showed suitable mesopore-dominated micro-mesoporous structures with high surface area of 1795.5 m2/g, large mesoporous volume of 0.87 m3/g, 3.65 % N-doping and excellent conductivity. Its unique hierarchical porous structure and abundant active sites facilitated the ion rapid insertion and extraction. When utilized to capture low-concentration nickel (Ni2+) ions, ENHPCLKG delivered splendid salt removal capacity of 17.86 mg/g, rapid average salt removal rate of 0.99 mg/g/min and standout cycle stability. Meanwhile, ENHPCLKG was further extended to remove NaCl, MgCl2, CaCl2 and Ni-containing wastewater, showing superior CDI property. Moreover, the recycled ENHPCLKG (10th) taken to eliminate indomethacin (IDM) depicted a splendid adsorption capacity. This work proved the significant applicant potential of the novel and green ENHPCLKG for disposing of Ni2+ ions via CDI technology.

Mesopore-enhanced graphene electrodes with modified hydrophilicity for ultrahigh capacitive deionization

Capacitive deionization (CDI) technology represents a potent approach towards energy-efficient and sustainable access to potable water, with minimal environmental impact. However, the ion removal capacity of CDI systems remains inadequate for desalination of saline water. Herein, mesopore-enhanced graphene foam with modified hydrophilicity via O2-plasma treatment (MGFP) is proposed for ultrahigh CDI. This developed MGFP encompasses abundant mesopores, outstanding electrical conductivity and good hydrophilicity, enabling fast ions migration, efficient solution/pores contact and high adsorption capacity. As such, MGEP delivers a high specific capacitance of 156.64 F g−1 at 1 mV s−1, and a maximum salt adsorption capacity (SAC) up to 40.76 mg g−1 (1000 mg L−1, 1.2 V), much higher than most of the CDI systems leveraging the carbon-based materials. What's more, MGFP can be employed in the treatment of wastewaters containing various heavy metals, with the SAC of 89.96, 83.38, and 91.80 mg g−1, as for CuCl2, CoCl2, and NiCl2 (1000 mg L−1, 1.6 V), respectively. This well-developed MGFP undoubtedly presents a promising material platform within the CDI system, effectively tackling the pressing concern of water scarcity.

Interfacial assembled porous bismuthene/Ti3C2Tx MXene heterostructure for highly efficient capacitive deionization

Capacitive deionization (CDI) is perceived as a promising technology for freshwater production owing to its environmentally friendly nature and low energy consumption. To date, the development of high-performance electrode materials represents the foremost challenge for CDI technology. In this work, the porous bismuthene/MXene (P-Bi-ene/MXene) heterostructure was synthesized using a simple interfacial self-assembly method with two-dimensional (2D) bismuthene and Ti3C2Tx MXene. Within the P-Bi-ene/MXene heterostructure, the porous structure can increase the active site and facilitate ion transport. Simultaneously, MXene effectively enhances the conductivity of the heterostructure, resulting in accelerating electron transport. Due to these attributes, the P-Bi-ene/MXene heterostructure demonstrates high desalination capacity (90.0 mg/g), fast desalination rate, and good cycling performance. The simple self-assembly strategy between 2D/2D materials described herein may offer inspirations for the synthesis of innovative electrode materials with high performance.

(Invited) Capacitive Deionization (CDI) – an Industrial Research Perspective

As the demand for freshwater keeps increasing due to industrialization and population growth, the world is progressively interested in desalination for sourcing potable water. While membrane-based reverse osmosis (RO) and thermal-based evaporation/distillation are proven technologies for desalination, they are also expensive. Capacitive deionization (CDI) - introduced in the 1970s - where the positive and negative ions are separated by the application of an electric field across pairs of high surface area electrodes, has been considered as a potentially cheaper technology. In the mid-2000s, Corning carried out a research project on developing CDI. The workstreams involved developing novel materials for electrodes, new device architecture, predictive theoretical models at electrode and device scales, and eventually a plant-level cost analysis that connected the electrode and device-level parameters to the final cost of water desalination, in $/gallon, which is the ultimate arbiter for techno-economic feasibility. We made significant progress in: (a) developing thin all-carbon electrodes which were electrochemically inert, highly conductive, and possessed high specific capacitance (F/cc) (b) designing a flow-past device architecture based on stacked planar electrodes with a small footprint (c) developing user-friendly simplified theoretical models, and (d) formulating two high-level figures of merit (FOM), namely, volumetric efficiency (VE) and recovery ratio (RR) – both of which need to be maximized to compete against incumbent technologies such as RO, especially in the high-throughput brackish water market sector. Our prototype achieved an equivalent VE of ~40 kg/ft3/day of salt removal. However, the plant-level cost analysis suggested that there is not much room for improving the overall cost structure compared to RO even with such high device level performance for high throughput desalination markets. In this talk we will present our experience with the development of CDI technology. We will cover all aspects of the project - electrode materials development, device architecture, theoretical models, and cost analysis – and will also offer an industrial perspective on CDI technology development, particularly when it comes to competing against well-established and entrenched technologies. We will also highlight how systems-level thinking and analyses are extremely important for such technology assessments and point out that only focusing on lab-scale performance metrics can be misleading.

(Invited) Lessons in Electrode Architecture for Faradaic Desalination

Potable water is an essential supply for humanitarian missions worldwide, yet delivering pre-purified water to remote locations is challenging, dangerous, and expensive. Therefore, it is desirable to develop and deploy on-site and portable desalination/water-purification equipment that draws on local water sources. Present reverse-osmosis systems effectively desalinate seawater, but are energy and time-intensive, require regular maintenance due to membrane fouling, and suffer from poor scalability. Capacitive deionization (CDI) technology provides energy-efficient desalination of brackish waters, but its use remains limited by low-capacity carbon-only electrodes that rely on double-layer ion storage. Transitioning to electrodes that also incorporate Faradaic ion-capturing materials with substantively higher storage capacity expands the efficacy and applicability of CDI. As one example, NRL-developed porous carbon nanofoam (CNF) architectures infiltrated with electrolessly deposited nanometric MnO2 demonstrate 6-fold increase in sodium-ion adsorption capacity compared to bare-carbon CNFs, while solvothermally deposited BiOCl renders a high-capacity chloride-ion adsorption electrode. The tunability of CNFs as an electrode scaffolding affords the opportunity to balance ion-storage capacity and electrolyte transport for optimized desalination performance. Lessons of electrode architecture extend to NRL silver “sponge” electrodes that provide high capacity for chloride, fast uptake dynamics, and opportunities for various flow configurations. Continued progress in bench-top level flow-cells with high-capacity faradaic materials will demonstrate the promise of this technology en route to development of larger-scale prototype desalination devices.

Application and Optimization of Capacitive Deionization Technology in Seawater Desalination

In this paper, the application and optimization of capacitive deionization technology in seawater desalination is studied. First, the limitations of the traditional desalination technology are reviewed, and the advantages of capacitive deionization technology are introduced. Then, the basic principles of capacitive deionization technology, including electric field effect and processes such as ion migration and charge adsorption, are introduced in detail. In terms of key components, the capacitor (electrolytic cell), electrolyte solution, power supply and control system are highlighted. Then, the optimization methods of capacitor deionization technology are discussed, including the selection and improvement of electrode materials, the optimization of electrolyte solution and the optimization of operating parameters. Finally, the optimization results and effects are analyzed, including improved removal rate and desalination effect, improved energy efficiency, increased water flux and water production capacity, extended maintenance intervals and improved stability, and improved cost effectiveness. This study has important implications for the application and optimization of capacitive deionization technology in seawater desalination.

Selective recovery of medium-chain fatty acids from secondary fermentation broth by flow-electrode capacitive deionization

Medium-chain fatty acids (MCFAs) can be produced using precursors from anaerobic digestion, which have greater application potential than methane. However, MCFAs recovery is challenged by the high energy and/or reagent consumption. To bridge this gap, in this study, the feasibility was demonstrated using flow-electrode capacitive deionization (FCDI) technology for the recovery of MCFAs from secondary fermentation broth. Results showed that caproate was selectively recovered and adsorbed on the carbon materials, while acetate and butyrate were mainly recovered and dissolved in the anolyte. Under the optimal conditions, a high selectivity (51.6%) and recovery concentrations (9.26 ± 0.37 g/L) of caproate were achieved. Besides, catholyte in FCDI was used as an in-situ generated desorbent for MCFAs recovery, which could guide the process design. In addition, as a technical optimization, nickel foam as an alternative anode decreased Faradaic oxidation of carboxylates. Overall, this study demonstrated that FCDI could be served as a new separation and purification technology to facilitate valuable MCFAs recovery.