Conventional Capacitive Deionization Research Articles

Novel flow-electrode capacitive deionization system employing modified MOF-derived carbon electrodes for metal ion removal

Activated carbon (AC) as an electrode for capacitive deionization (CDI) is constrained by its low specific surface area and specific capacitance, leading to electrical double layer overlap (EDL). To address this issue, a flow electrode capacitive deionization system (MDC-FCDI) was developed, which used modified MOFs-derived carbon (MDC) as the electrode. The MDC electrode exhibited enhanced specific capacitance (145.78 F/g) and specific surface area (2458.44 m2/g). Compared to conventional FCDI, the MDC-FCDI system demonstrated a 35–39 % improvement in heavy metal removal efficiency from wastewater containing Pb2+, Cu2+, Cd2+, and Zn2+. The selectivity of MDC-FCDI for heavy metals exhibited a unique “two-step phenomenon” that differed from what was observed in conventional CDI systems. In the MDC-FCDI system, high-valent ions experienced stronger electric field forces and preferentially occupied active sites on the electrode surface prior to the adsorption of ions with lower valence. The selectivity of the MDC-FCDI system for heavy metal ions is determined by three factors in the following order of priority: ionic charge, hydration radius, and ion feed concentration. This study offers a practical approach for expanding the range of MDC-FCDI applications.

Engineering Faradaic Electrode Materials for High-Efficiency Water Desalination.

Water desalination technologies play a key role in addressing the global water scarcity crisis and ensuring a sustainable supply of freshwater. In contrast to conventional capacitive deionization, which suffers from limitations such as low desalination capacity, carbon anode oxidation, and co-ion expulsion effects of carbon materials, the emerging faradaic electrochemical deionization (FDI) presents a promising avenue for enhancing water desalination performance. These electrode materials employed faradaic charge-transfer processes for ion removal, achieving higher desalination capacity and energy-efficient desalination for high salinity streams. The past decade has witnessed a surge in the advancement of faradaic electrode materials and considerable efforts have been made to explore optimization strategies for improving their desalination performance. This review summarizes the recent progress on the optimization strategies and underlying mechanisms of faradaic electrode materials in pursuit of high-efficiency water desalination, including phase, doping and vacancy engineering, nanocarbon incorporation, heterostructures construction, interlayer spacing engineering, and morphology engineering. The key points of each strategy in design principle, modification method, structural analysis, and optimization mechanism of faradaic materials are discussed in detail. Finally, this work highlights the remaining challenges of faradaic electrode materials and present perspectives for future research.

Emerging Frontiers in Multichannel Membrane Capacitive Deionization: Recent Advances and Future Prospects.

Capacitive deionization (CDI) has emerged as a promising desalination technology and recently promoted the development of multichannel membrane capacitive deionization (MC-MCDI). In MC-MCDI, the independent control of multiflow channels, including the feed and electrolyte channels, enables the optimization of electrode operation in various modes, such as concentration gradients and reverse voltage discharge, facilitating semicontinuous operation. Moreover, the integration of redox couples into MC-MCDI has led to advancements in redox-mediated desalination. Specifically, the introduction of redox-active species helps enhance the ion removal efficiency and reduce energy consumption during desalination. This systematic approach, combining principles from CDI and electrodialysis, results in more sustainable and efficient desalination. These advancements have contributed to improved desalination performance and practical feasibility, rendering MC-MCDI an increasingly attractive option for addressing water scarcity challenges. Despite the considerable interest in and potential of this process, there is currently no comprehensive review available that covers the operational features and applications of MC-MCDI. Therefore, this Review provides an overview of recent research progress, focusing on the unique cell configuration, vital operation principles, and potential advantages over conventional CDI. Additionally, innovative applications of MC-MCDI are discussed. The Review concludes with insights into future research directions, potential opportunities in industrial desalination technology, and the fundamental and practical challenges for successful implementation.

Organic Faradaic Desalination Cell Based on Polyimide Symmetric Electrodes

Capacitive deionization (CDI) is an energy-efficient and environmentally friendly deionization technology. However, the maximum desalination capacity of conventional carbon-based CDI systems is in the range of 5–25 mg g-1, which compromises the use of this technology in practical applications [1]. Faradaic deionization (FDI) is a promising electrochemical technique, based on storing the ions within the particles/layers of the electrode materials either by intercalation and/or faradic reactions. By this mechanism, FDI has expanded the deionization values above 50 mg g-1. In the last ten years, research on FDI has primarily focused on battery electrode materials, especially in inorganic intercalation compounds, typically used for energy storage [2]. However, inorganic materials have several drawbacks, such as decomposition and dissolution issues, which affect long-term performance along with safety and sustainability aspects and consequently might limit their practical deployment.As an alternative, we introduce in this work for the first time an all-polymer deionization cell in combination with a rocking-chair desalination (RCD) mechanism with the aim of boosting the deionization performance [3]. A proof-of-concept next generation technology is accomplished by using a redox-active naphthalene-polyimide (poly[N,N′-(ethane-1,2-diyl)-1,4,5,8-naphthalenetetracarboxiimide], named as PNDIE), which is a well conductive and free-standing electrode material, as anode and cathode in a symmetric FDI system. Our approach relies on the synergistic combination of smart redox polymer selection i.e. PNDIE, and the advance configuration of this material into a buckypaper electrode architecture. A detailed electrochemical characterization under various operational conditions in three electrodes standard half-cell and in two electrode coin-cell configurations was performed. The results of those experiments provide critical information to build an all-polymer rocking chair system with practical PNDIE electrodes (92.2 mgPNDIE; 9.6 cm2). This novel FDI lab-cell demonstrated a remarkable desalination capacity (155.4 mg g-1 at 0.01 A g-1) together with a high salt-removal rate and productivity (3.42 mg g-1 min-1 at 0.01 A g-1 and 62 L h-1 m-2, respectively). In addition, long-term stability experiments provided salt adsorption capacity retention values over 95 % after 100 cycles (23 days). Compared to the state-of-the-art deionization technologies (CDI, Hybrid CDI and FDI) the reported technique exhibits superior electrochemical and deionization performance. These results support the idea of using organic materials as a viable alternative for robust and sustainable “water-energy” electrochemical applications.

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.

Study on influencing factors of capacitive deionization with Prussian blue analog/activated carbon electrode

Membrane Capacitive Deionization (MCDI) is an efficient desalination technology using ion-selective membranes and capacitive principles to remove ions. Highly mineralized water flows through parallel electrode plates separated by ion-selective membranes. An applied electric field adsorbs ions onto electrodes, creating an electric double layer, and periodic field reversals release enriched ions back into the water while discharging ions on the electrode surfaces, enabling continuous deionization. This study aims to investigate the feasibility of using MCDI technology with Prussian blue analog (PBA)/carbon electrodes to treat highly mineralized water in oilfields. The desalination rate under different operating conditions is experimentally analyzed and compared. A comparison is made between the Capacitive De-Ionization (CDI) systems in terms of changes in conductivity, desalination rate, ion adsorption capacity, and ion adsorption rate. Results showed that compared to conventional CDI and Hybird-CDI (HCDI), MCDI demonstrates the highest desalination rate, ion adsorption capacity, and ion adsorption rate. It indicates that MCDI has significant advantages in treating highly mineralized water. At a voltage of 1.6 V, a flow rate of 30 mL·min−1, and an initial concentration of 1000 mg·L−1, the MCDI system exhibited the highest desalination efficiency. Under these conditions, the desalination rate was 43.4%, the electrosorption capacity was 54.75 mg·g−1, and the electrosorption rate was 0.018 mg·g−1·s−1. The study provides a viable solution for the treatment of highly mineralized water in oilfields and serves as a reference for further improvement and application of MCDI technology.

Functional anode of membrane capacitive deionization enabled by Cu2+/Cu+ redox couple for simultaneous anions removal and anodic oxidation mitigation

Activated carbon (AC) based conventional capacitive deionization has shown extraordinary promise for energy efficient water treatment, but its capacity and cycle stability are limited by the mechanism of electric double-layer and the oxidation of anode, respectively. Redox electrolytes are proposed as one of the most promising strategies to improve the charge storage capacitance. Here, functional anode enabled by Cu2+/Cu+ redox couple is constructed by adding 10 mM CuCl2 into 100 mM NaCl supporting electrolyte. A membrane capacitive deionization (MCDI) cell with the functional anode and anion exchange membrane, employing a two channel structure is proposed to remove the anions (F−, Cl−) from wastewater. The reverse constant current discharge mode with 1.2 V/−1.2 V cut-off voltage can realize Cu2+/Cu+ redox reaction. The water production rate of the MCDI cell is above 50 % and the Cl− removal capacity is increased by 163 % due to the additional faradaic process. The cell capacity can be maintained above 83 % after 40 cycles. In particular, fast charge balance and redox couple reaction processes of this functional anode could significantly alleviate the oxidation of the anode AC electrode. This work provides new opportunities for developing cost-effective technologies to remove the anions from wastewater.

In situ synthesis of ultrasmall NaTi2(PO4)3 nanocube decorated carbon nanofiber network enables ultrafast and superstable rocking-chair capacitive deionization

Faradic-based capacitive deionization (CDI), as an important derivative of conventional CDI, has received wide attention in the desalination community. Yet, oriented from its intrinsic ion storage mechanism, faradic-based CDI has been plagued by several serious issues (e.g., imbalanced ion storage capacity, low desalination rate, and poor cycling stability), which greatly constrained its further development. Herein, we put forward an innovative strategy by using carbon nanofiber-reinforced NaTi2(PO4)3 (eCNF/NTP) as the core material (for Na+-capturing) and further coupling it with rational rocking-chair capacitive deionization (RCDI) cell architecture. Of note, owing to the unique 3D network structure of eCNF/NTP that not only provides sufficient redox-activate sites but also offers a rigid network structure to prevent the potential aggregation during cycling, as well as the rational RCDI symmetric cell architecture to avoid the imbalanced cation and anion storage capacity, the RCDI system equipping with eCNF/NTP electrode displays an excellent desalination performance (desalination capacity: 168.2 mg g−1; desalination rate: 0.46 mg g−1 s−1) with outstanding cycling stability (only 6 % desalination capacity degradation after 80 cycles). This work is interesting because it showcases the critical importance of both delicate material design and rationalized cell architecture in addressing the bottleneck issue of CDI, which could shed light on the future development of other high-performance desalination systems.

A high performance all-polymer symmetric faradaic deionization cell

Faradaic deionization (FDI) is an emerging and promising electrochemical technology for stable and efficient water desalination. Battery-type energy storage materials applied in FDI have demonstrated to achieve higher salt removal capacities than carbon-based conventional capacitive deionization (CDI) systems. However, most of the reported FDI systems are based on inorganic intercalation compounds that lack cost, safety and sustainability benefits, thereby curtailing the development of a feasible FDI cell. In this work, we introduce an all-polymer rocking chair practical FDI cell, with a symmetric system composed by a redox-active naphthalene-polyimide (named as PNDIE) buckypaper organic electrodes. First, electrochemical performance of PNDIE in 0.05 M NaCl under open-air conditions is evaluated in both three-electrode half- and symmetric FDI full-cell using typical lab-scale electrode dimensions (1.6 mgPNDIE; 0.78 cm2), revealing promising specific capacity (115 mAh g−1) and excellent cycle stability for full-cell experiments (77 % capacity retention over 1000 cycles). Then, all-polymer rocking chair FDI flow cell was constructed with practical PNDIE electrodes (92.2 mgPNDIE; 9.6 cm2) that delivered large desalination capacity (155.4 mg g−1 at 0.01 A g−1) and high salt-removal rate and productivity (3.42 mg g−1 min−1 at 0.04 A g−1 and 62 L h−1 m−2, respectively). In addition, long-term stability (23 days) experiments revealed salt adsorption capacity (SAC) retention values over 95% after 100 cycles. The overall electrochemical and deionization performances of the reported technology is far superior than the state-of-the-art CDI and FDI techniques, making it a competitive choice for robust and sustainable “water-energy” electrochemical applications.

Controllable synthesis of nickel–cobalt-doped Prussian blue analogs for capacitive desalination

The unique framework structure of Prussian blue imparts excellent sodium storage capacity and cycling stability, thus making it an ideal capacitive deionization (CDI) electrode. Herein, Prussian blue analogs were prepared by the controlled doping of nickel–cobalt bimetallic ions to improve their desalination capacity and stability. Process parameters such as cell potential, current, inlet flow rate, and solution concentration were investigated to determine the optimal conditions for Prussian blue desalination, and a high-performance Prussian blue analog (CNF-4) was successfully synthesized by accurately controlling the nickel–cobalt doping ratio. The desalination capacity and rate of CNF-4 (Ni:Co=1:2) reached 65.31 mg g−1 and 4.38 mg g−1 min−1, respectively, and 98% of the capacity retention rate was maintained after 50 cycles of desalination. The excellent capacity and performance of the CNF-4 material indicate its superiority to conventional PBA CDI electrodes and its prospective applications in seawater desalination.

Ammonia Removal from Simulated Wastewater Using Ti3C2T x Mxene in Flow Electrode Capacitive Deionization

The energy-water nexus poses an integrated research challenge with crucial global implications. The nexus highlights the need to adopt a proactive approach by focusing on the conservation and management of both resources. As global freshwater supply continues to deplete, a larger number of people in the world will need to rely on recycled water. One of the ways to address this concern is by focusing efforts on the development and deployment of energy efficient water remediation technologies. Ammonia is one of the most common contaminants found in domestic and industrial wastewater. Concurrently, it is also one of the most liberally produced chemicals because of its widespread use in the agricultural and textile industries. In 2020, approximately 144 million metric tons of ammonia were produced globally (1). Despite that, biological nitrification remains the most widespread method for treating ammonia wastewater (2). Aside from being cumbersome and slow, it also fails to recover ammonia, which is otherwise a valuable product. In pursuit of sustainability, product conservation directly translates to energy conservation and there remains a need for a water purification and ammonia recovery technology that is energy, water, and resource efficient. Capacitive deionization (CDI) is a separation technology that removes ions from water by applying a small voltage below the dissociation potential of water (1.23 V). The ions are temporarily stored in the electrodes and later released to a separate concentrated stream upon voltage removal or reversal. Flowing electrode CDI systems (FE-CDI) have proven advantageous because of their ability to prevent cross contamination, and to run in uninterrupted cycles ad infinitum . The performance of FE-CDI systems relies on the selection of suitable electrode materials with desired properties of high electrical conductivity, high surface area, colloidal stability, and surface sensitivity (3). MXenes are an emerging class of two-dimensional (2D) materials that are highly conductive, hydrophilic, tunable, and possess attractive charge storage and ion transport properties (4,5). In this work, we developed a flowing electrode capacitive deionization (FE-CDI) system using Ti3C2T x MXene suspension electrodes for the removal and recovery of ammonia from synthetic wastewater. A custom-built FE-CDI unit using titanium current collectors with an effective transfer area of 10 cm2 was used to test system efficiency. The electrode performance was evaluated by operating the CDI system with a feed solution of 500 mg/L NH4Cl running in batch mode at a constant voltage of 1.2 and -1.2 V in charging and discharging stages respectively. Despite low loading (1 mg/ml), Ti3C2T x flow electrodes showed a markedly improved performance by achieving 60% ion removal efficiency (Fig. 1a) in a short saturation time of 115 minutes, and an unprecedented ion adsorption capacity of 460 mg/g (Fig. 1b). This is ~ 7× higher than the currently reported value using Ti3C2 in a conventional CDI system targeted at sodium chloride (NaCl) desalination (6). Post-mortem characterization of the suspension electrodes by X-ray diffraction revealed that Ti3C2T x MXene sequestered high amounts of pollutants due to its ability to intercalate ions between its 2D layers. The electrodes possessed favorable electrochemical properties with a high specific capacitance of 148 F/g. The system proved to be a green technology by exhibiting satisfactory charge efficiency of 58-70% while operating at a relatively low energy consumption of 0.45 kWh/kg (Fig. 1c), which is about an order of magnitude lower than the 4.6 kWh/kg used by commercial wastewater treatment plants (7). The results demonstrate that the Ti3C2T x MXene electrodes have the potential to improve the FE-CDI process for energy-efficient removal and recovery of ammonia. IEA, Ammonia Technology Roadmap, International Energy Agency, Paris, (2021).F. Jaramillo, M. Orchard, C. Muñoz, M. Zamorano, and C. Antileo, J. Environ. Manage., 218, 154–164 (2018).Y. Oren, Desalination, 228, 10–29 (2008).Y. Gogotsi and B. Anasori, ACS Nano, 13, 8491–8494 (2019).P. Singh et al., J. Power Sources, 506 (2021).J. Ma, Y. Cheng, L. Wang, X. Dai, and F. Yu, Chem. Eng. J., 384 (2020).M. Ekman, B. Björlenius, and M. Andersson, Water Res., 40, 1668–1676 (2006). Figure 1

An open-source deep learning model for predicting effluent concentration in capacitive deionization

To effectively evaluate the performance of capacitive deionization (CDI), an electrochemical ion separation technology, it is necessary to accurately estimate the number of ions removed (effluent concentration) according to energy consumption. Herein, we propose and evaluate a deep learning model for predicting the effluent concentration of a CDI process. The developed deep learning model exhibited excellent prediction accuracy for both constant current and constant voltage modes (R2 ≥ 0.968), and the accuracy increased with the data size. This model was based on the open-source language, Python, and the code has since been distributed with proper instructions for general use. Owing to the nature of the data-oriented deep learning model, the findings of this study are not only applicable to conventional CDI but also to various types of CDI (membrane CDI, flow CDI, faradaic CDI, etc.). Therefore, by referring to the examples shown in this study, we hope that this open-source deep learning code will be widely used in CDI research.

ZIF-67 metal-organic frameworks and CNTs-derived nanoporous carbon structures as novel electrodes for flow-electrode capacitive deionization

Capacitive deionization (CDI) has been attracting great interest as a promising desalination technology during the last decade because of its energy, cost effectiveness, and eco-friendly process. In particular, CDI using flowable electrodes (FCDI) offers a continuous desalination stream without the need for discharging and much better salt removal than that of conventional CDI desalination technologies. Nevertheless, FCDI desalination still suffers from the inherent low electrical conductivity of its liquid slurry electrode, which results in high internal and interfacial resistances and limits the salt-removal performance of the FCDI desalination system. In this study, in order to improve the electrical conductivity of flow electrodes, we synthesized zeolitic imidazolate frameworks (ZIF-67), made of the widely investigated Zn/Co-based MOFs, onto CNT templates ([email protected]) and investigated their FCDI desalination performance. The salt removal rate for [email protected] included flow electrodes reached 1.09 mmol/m2s, which is a 57% increase over that of pristine AC (0.69 mmol/m2s), with a salt-removal efficiency of 37.3%. Electrochemical analyses including CV and EIS measurements confirmed that such improved salt removal performance originates from the enhanced electrical conductivity by the formation of a conducting bridge between the suspended AC particles in the slurry electrodes.

(Invited) Electrochemical Ion Separation Based on Capacitive Deionization as Promising Water and Resource Recovery Processes

To resolve the global issue of the water crisis, capacitive deionization (CDI) has been suggested as a promising water recovery technology via electrochemical ion separation. It is considered as an alternative or competing technology for conventional water purification systems such as reverse osmosis and multistage flash distillation. CDI has attracted numerous academic and industrial attention as a novel desalination process for its unique advantages such as high energy efficiency, environmental friendliness, and a high water recovery rate.In the conventional CDI cell architectures, typically a pair (or multiple pairs) of porous carbon electrodes are used, separated by a spacer.The operation of the CDI system consists of two cycles including charging (purification/electro-adsorption) and discharging (regeneration/electro-desorption) steps. During the charging step, the porous electrode pair is charged with applied potential, and salt ions are electro-adsorbed into the electrical double layer (EDL) generated between the interface of porous electrode and water, leading to the removal of salt ions from the feed aqueous solution. The adsorbed ions are released from the electrodes in the discharging step, which is operated with reversed polarity, or short circuit resulting in a concentrated effluent stream.Since the 21st century, numerous technological advancement has been achieved and the field of application has extended thanks to the efforts of research groups around the world. In this presentation, we aim to introduce the major operating principles and research advances including electrode materials and cell configurations. Also, the various applications of CDI are briefly introduced. Finally, this presentation proposes future research directions for the scientific and industrial challenges in water and resource recovery technologies.

Recent Advances in Faradic Electrochemical Deionization: System Architectures versus Electrode Materials.

Capacitive deionization (CDI) is an energy-efficient desalination technique. However, the maximum desalination capacity of conventional carbon-based CDI systems is approximately 20 mg g-1, which is too low for practical applications. Therefore, the focus of research on CDI has shifted to the development of faradic electrochemical deionization systems using electrodes based on faradic materials which have a significantly higher ion-storage capacity than carbon-based electrodes. In addition to the common symmetrical CDI system, there has also been extensive research on innovative systems to maximize the performance of faradic electrode materials. Research has focused primarily on faradic reactions and faradic electrode materials. However, the correlation between faradic electrode materials and the various electrochemical deionization system architectures, i.e., hybrid capacitive deionization, rocking-chair capacitive deionization, and dual-ion intercalation electrochemical desalination, remains relatively unexplored. This has inhibited the design of specific faradic electrode materials based on the characteristics of individual faradic electrochemical desalination systems. In this review, we have characterized faradic electrode materials based on both their material category and the electrochemical desalination system in which they were utilized. We expect that the detailed analysis of the properties, advantages, and challenges of the individual systems will establish a fundamental correlation between CDI systems and electrode materials that will facilitate future developments in this field.

Capacitive-faradaic fuel cells (CFFCs) for ion separation: Macro-scale configurations and polarization mechanism

The polarization mechanism of capacitive-faradaic fuel cells is reported. The mixed potentials of faradaic (Pt and Ti/Pt-IrO2) and capacitive (activated carbon powder and fleece) electrodes were measured in aerated and hydrogenated NaCl solutions at various pH values. Next, two configurations featuring divided and undivided macro-scale CFFCs were investigated: (i) a system with two fixed electrodes made of Ti/Pt-IrO2 and activated carbon fleece, and (ii) a CFFC with one fixed Ti/Pt-IrO2 electrode and one flowing carbon electrode. The salt adsorption capacities obtained in both systems were low compared to conventional capacitive deionization, and therefore optimization of materials and cell architecture is needed. The behaviour of pH and Cl−, SO42− anions conforms to the proposed capacitive-faradaic mechanism, but that of NH4+ and Na+ cations contradicts it. This phenomenon is attributed to faradaic processes and the competitive adsorption–desorption of H+ and OH− ions, which require further detailed investigation.

Faradaic Electrodes Open a New Era for Capacitive Deionization.

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

Enhanced salt removal performance of flow electrode capacitive deionization with high cell operational potential

Capacitive deionization (CDI) is an emerging technology with great potential to be energy efficient and allow cost-effective operation for the removal of salt ions from saline water. The introduction of flow electrode to CDI greatly enhanced the salt removal performance at much higher salt concentration, even at seawater level, due to not needing a discharging process, which is required for conventional CDI desalination. Since the oxidation of carbon electrodes and water electrolysis leads to the decrease in desalination performance and long-term stability of the CDI cell, it has typically been operated at the potential difference < 1.2 V. However, due to the various resistances of CDI components, it is known that the electrode potential is lower than the applied cell potential difference. Based on such knowledge, in this study, we operated FCDI desalination at various operational potential differences from 1.2 to 4.5 V, and studied the carbon oxidation and electrochemical characteristics by FT-IR, Raman spectroscopy, and EIS measurements. Desalination efficiency and salt removal rate increase with higher operational potential difference. Our results confirmed that up to 2.5 V, no noticeable carbon oxidation and gas generation resulting from water electrolysis occurred.

Graphene Oxide-Tuned MoS2 with an Expanded Interlayer for Efficient Hybrid Capacitive Deionization

Capacitive deionization (CDI) has shown great promise in desalinating salt water; however, conventional CDI electrode materials suffer from low specific salt capacity and charge efficiency owing to...

Exploration of Energy Storage Materials for Water Desalination via Next-Generation Capacitive Deionization.

Clean energy and environmental protection are critical to the sustainable development of human society. The numerous emerged electrode materials for energy storage devices offer opportunities for the development of capacitive deionization (CDI), which is considered as a promising water treatment technology with advantages of low cost, high energy efficiency, and wide application. Conventional CDI based on porous carbon electrode has low salt removal capacity which limits its application in high salinity brine. Recently, the faradaic electrode materials inspired by the researches of sodium-batteries appear to be attractive candidates for next-generation CDI which capture ions by the intercalation or redox reactions in the bulk of electrode. In this mini review, we summarize the recent advances in the development of various faradaic materials as CDI electrodes with the discussion of possible strategies to address the problems present.