Capacitive Deionization Electrodes Research Articles

Exploring the Use of Static Mixers for Enhanced Flow-Electrode Capacitive Deionization

Water desalination plays a major role in alleviating water scarcity issues, but it faces major barriers due to high energy use, low water utilization, and significant environmental impacts. Flow electrode capacitive deionization (FCDI) is a new ultra-efficient electrochemical water treatment technology capable of desalinating saline streams (e.g., brackish water, seawater) with less than 10% of the feed water rejected as waste. Here we use a structured flow plate design to maximize charge transfer while incurring a negligible pressure drop penalty. Different 3D printed flow plate structures were characterized individually in a flow capacitor arrangement to quantify their relative merits in terms of the tradeoff between conductivity and flow characteristics with carbon slurries containing 5-9 wt% activated carbon and 0-1 wt% carbon black.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Funding was provided by Lawrence Livermore National Laboratory Directed Research and Development (LDRD) Grant 22-DR-011. IM #LLNL-ABS-846456

Enhancing U(VI) removal by using biomass-derived hierarchical porous carbon/α-MnO2 nano fiber composites as high hybrid capacitance electrodes for capacitive deionization

The radioactive pollution caused by uranium containing wastewater generated during the nuclear fuel cycle seriously threatens human health and environmental safety. The electrosorption (or capacitive deionization, CDI) separation of U(VI) from wastewater has the advantages of high efficiency, low energy consumption, convenient operation, and no secondary pollution, making it a promising new separation technology. By combining double layer capacitive materials with pseudo capacitive materials, the specific capacitance and ion storage capacity of the composites can be significantly improved, thereby improving the electrosorption performance. This work used natural biomass as raw material to prepare hierarchical porous biocarbon through high-temperature pyrolysis and chemical activation, and then it was incorporated with hydrothermally synthesized α-MnO2 nanofibers to obtain novel composites (BC/α-MnO2) with high hybrid capacitance for U(VI) removal in CDI. The electrochemical characteristics of the composites and their electrosorption performances for U (VI) were respectively investigated in a three electrode system and a CDI device. The results suggested that BC/α-MnO2 exhibited an ideal capacitive behavior, and theoretical calculations indicated the synergistic effect of capacitive and diffusion control processes on ion storage. Among different BC/α-MnO2 electrodes, BC/α-MnO2-2 had the highest specific capacitance (130.48 F/g) and also the highest adsorption capacity for U (VI) (280.20 mg/g at 0.9 V and pH 4.0). The isotherms and kinetics of U (VI) electrosorption were consistent with the Langmuir and PFO models, respectively. The electrosorption mechanism was mainly related to the contribution of pseudocapacitance and EDL adsorption. Overall, BC/α-MnO2-2 exhibited ideal electrochemical properties and excellent electrsorption performance for U (VI) (high electrosorption capacity, fast kinetic rate, and good cycling stability), facile fabrication and environmentally friendly, and thus it has promising application in CDI treatment of radioactive wastewater.

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.

Rational design of sea urchin-like FeOOH anchored hollow carbon spheres as chloride-insertion electrodes for efficient faradic capacitive deionization

Faradic capacitive deionization (FDI) is one of the most promising branches of capacitive deionization (CDI) to relieve global water stress. However, the problems of slow desalination kinetics and poor cycle stability of the anode of FDI have greatly restricted the development of its practical applications. Herein, we put forward a strategy of employing hollow carbon spheres (HCSs) with high specific surface area, and good electrical conductivity/stability as the structural backbone and further decorated it with FeOOH nanorod to construct a 3D sea urchin-like structure (HCSs@FeOOH) as the anode for FDI. Notably, the essence of this design is the structural backbone (HCSs) could not only prevent the structural agglomeration between FeOOH but also provide good electric conductivity to the material system to realize superior pseudo-capacitance. As a result, the HCSs@FeOOH-based FDI system displays excellent desalination performance (desalination capacity and rate up to 69.48 mg g−1 and 0.37 mg g−1 s−1) with good durability (only 14.32 % desalination capacity decrease over 100 cycles), respectively.

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.

A novel flow electrode capacitive deionization device with spindle-shaped desalting chamber

A novel flow electrode capacitive deionization device with spindle-shaped desalting chamber

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.

Highly dispersed ultrasmall BiOCl nanoclusters on graphene sheets as high-performance anion-capture electrode for hybrid capacitive deionization

BiOCl nanomaterials, because of their unique layered structure and fascinating physicochemical properties, have attracted enormous attention as anode material for capacitive deionization (CDI) towards the relief of global freshwater scarcity. However, the synthesis of ultrasmall BiOCl nanoclusters remains a considerable challenge, while the effect of crystalline surfaces on the Cl− ion intercalation/deintercalation has not yet been explored so far. In this work, highly dispersed BiOCl nanoclusters with the predominant exposure of (110) and (101) planes on graphene sheets (BiOCl@G) are fabricated by nanoconfinement and air-plasma strategy. On one hand, the ultrasmall BiOCl nanoclusters with size of ∼3 nm significantly increased their atomic utilization and electrochemical active sites, whereas the preferred crystalline planes of (110) and (101) favored the Cl− intercalation/deintercalation process within BiOCl. On the other hand, the dominant mesopores, along with a large interlayer distance (∼0.4 nm) between exfoliated graphene sheets, ensured the fast ion transport-adsorption at BiOCl/solution interface. With these novel structural features, the BiOCl@G possesses excellent figure-of-merits in terms of the Cl−-adsorption capacity (109.8 mg g−1), adsorption rate (0.110 mg g−1 s−1), energy consumption, and CDI cycling stability. These results provide new fundamental insights for developing high performance BiOCl-graphene nanocomposites used in CDI desalination and beyond.

New insights into the performance analysis of flow-electrode capacitive deionization using ferri/ferrocyanide redox couples for continuous water desalination

Flow Electrode Capacitive Deionization (FCDI) is a promising technology that uses carbon materials as flow electrodes in aqueous conditions to enable continuous desalination. In this work, the parametric investigation of the FCDI cell was carried out for low and high surface area activated carbon. When 1 mM/1 mM ferri-/ferrocyanide redox couple in the 1 M NaCl supporting electrolyte containing the 5 wt% high surface area activated carbon and 0.5 wt% MWCNT is circulated as flow electrode at the flow rate of 8 mL/min in the electrode chamber and 0.1 mM NaCl feed water is circulated in single-pass mode at 8 mL/min, the FCDI system achieved a significant improvement in desalination performance up to 76.38 % of SRE, with a high average salt removal rate of 43.925 µg/cm2s @ 2 V, charge efficiency of 20.11 % and average energy consumption of 0.27 kWh/mol, through a thorough parametric investigation. When the FCDI cell was tested with tap water, the average salt removal rate, average energy consumption, and salt removal efficiency were calculated at 6.11 μg/cm2s, 2.46 kWh/mol, and 46.61 % respectively, resulting in the reduction of total dissolved solids of 600 mg/L at the inlet to 365 mg/L at the outlet. The combination of microporous high surface area carbon and ferro-ferri redox couple propelled the desalination performance in comparison with the macroporous low surface area carbon, maximizing the ion removal rate, which further reduced the energy consumption and operating voltage for the process.

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.

Unravelling the enhanced capacitive desalination behavior of nanoneedle-like NiFe2O4

In this work, the nanoneedle-like NiFe2O4 (NFO) has been prepared by a template method and post annealing process for capacitive deionization (CDI) with enhanced performance. Owing to the unique structure, the nanoneedle-like NFO provides large accessible surface area, which benefits to offer abundant electroactive sites for electrosorption. Meanwhile, the salty ions diffusion and electron exchange are promoted by needle-like structure. Further, it is found that the NFO annealed at 450 °C (NFO-450) demonstrate the high crystallinity, rich mesopores and exceptional electrochemical properties. As electrode for CDI, the NFO-450 has manifested the high desalting capacity of 1.62 mmol/g when the effective loading mass of both electrodes is 23.6 mg. Interestingly, the desalting capacity realizes the linear correlation with the mass of NFO electrode ranging from 23.6 to 45.8 mg. The mechanism analysis stands out that the Na+ are captured by NFO, accompanied by the reduction of Ni3+ to Ni2+ in the 1st cycle. Afterwards, the Na+ can be electrostatically removed by the NFO//AC system.

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.

The regulation of biochar surface potential to achieve rapid capacitive deionization

Capacitive deionization (CDI) is a promising desalination technology. In the design and fabrication of high-performance CDI electrodes, the modification of activated carbon is widely adopted to improve the desalination capacity. In this work, aiming at the regulation of surface potential, activated carbon was doped with N and S, showing improved conductivity, wettability, and optimized pore structure. The difference in the potential of zero charge (Epzc) generated by the heteroatom doping was employed to enlarge the actual adsorption voltage window, and to improve the salt adsorption capacity (SAC) and total salt adsorption capacity at long periods. SAC of 14.4 mg g-1 was achieved with a high average salt absorption rate (ASAR) of 8.2 mg g-1 min-1 under 1.2 V in a 500 mg L-1 NaCl solution. Moreover, the total SAC of asymmetric configuration of N, S-doped biochar of 50 cycles achieved 545.8 mg g-1, 19.7% more than that of the symmetric configuration of unmodified biochar. The doping of N and S atoms on biochar brings excellent electrochemical performance and desalination capacity, and the rational utilization of Epzc after heteroatom doping provides a reasonable method for the design of CDI configuration.

Effective removal of trace arsenic from groundwater by capacitive deionization

In this paper, functionalized CNTs and Fe3O4 were compounded by co-precipitation method and the binder-free capacitive deionization (CDI) electrodes were innovative prepared by electrophoretic deposition (EPD) technique. The effects of applied voltage, flow rate and solution pH on the adsorption capacity of arsenic were investigated. The results confirmed that introduction of different functional groups (–COOH, -SO3H and -PO3H2) and composite transition metal oxide (Fe3O4) led to the materials not only with enhanced hydrophilicity but also with higher capacitance. The CDI test showed that trace arsenic can be effective treated to less 2 μg/L, which satisfied the World Health Organization (WHO) drinking water standard (below 10 μg/L). The CNTs-X@Fe3O4 electrode was found to maintain specific adsorption of arsenic through selectivity experiments. In addition, the combined electro-sorption and chemisorption effectively produce higher adsorption capacity, faster adsorption rate and high selectivity. Therefore, the electrode prepared by EPD has a high prospect of application in arsenic removal by CDI.

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.

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.

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.

Waste-derived stable carbon electrodes for capacitive deionization using poly (vinyl alcohol)-glutaraldehyde as binder

Waste-derived stable carbon electrodes for capacitive deionization using poly (vinyl alcohol)-glutaraldehyde as binder

Insights into the Particle Hydrophilicity and Electrical Conductivity for the Construction of a Highly Efficient Electrical Percolation Network in Flow Electrode Capacitive Deionization

Insights into the Particle Hydrophilicity and Electrical Conductivity for the Construction of a Highly Efficient Electrical Percolation Network in Flow Electrode Capacitive Deionization

Iron-containing biochar derived from dyeing sludge for high-performance capacitive deionization

The design and synthesis of high-performance, environmentally friendly, and economical electrode materials are essential for the development of energy-efficient capacitive deionization (CDI) technologies. As a strategy to turn waste into resource, abundant and low-cost sludge biomass materials are promising candidates for the preparation of CDI electrodes. In this work, a series of iron-containing dyeing sludge-derived biochar with different iron compounds were successfully prepared by direct pyrolysis followed by chemical modification treatment, and applied them as hybrid capacitive deionization (HCDI) cathodes for the first time. The ion adsorption capacity of HCDI electrode is up to 78.76 mg g−1 in 500 mg L−1 NaCl solution at 1.2 V and stable regeneration performance over 50 cycles. XPS measurements reveal that the storage mechanism of ions is a pseudocapacitance effect induced by the Fe2+/Fe3+ redox couple, enabling reversible and fast ion storage. The enhanced HCDI performance is ascribed to the well dispersed iron compounds active sites, rich pore structure and superior hydrophilicity. This work offers a promising strategy for the synthesis of high-performance HCDI electrode materials from sludge biomass, and demonstrates the superior pseudocapacitive performance of Fe2+/Fe3+ redox couple.