Enhanced Charge Efficiency and Electrode Separation Utilizing Magnetic Carbon in Flow Electrode Capacitive Deionization

Enhanced salt removal performance using nickel hexacyanoferrate/carbon nanotubes as flow cathode in asymmetric flow electrode capacitive deionization

Enhanced capacitive deionization for Cr(VI) removal from electroplating wastewater: Efficacy, mechanisms, and high-voltage flow electrodes

Equivalent film-electrode model for flow-electrode capacitive deionization: Experimental validation and performance analysis

Phosphate selective recovery by magnetic iron oxide impregnated carbon flow-electrode capacitive deionization (FCDI)

Flow electrode capacitive deionization (FCDI) is a newly developed water treatment technology that offers better performance than the original, solid electrode capacitive deionization (CDI). By eliminating the need for discharging process, FCDI provides much higher desalination capacity with a continuous desalination operation. Along with applications for salt removal, selective removal and recovery of specific ions are also prominent features of FCDI technology. Characteristics of electrodes and ion exchange membranes play a crucial role in controlling the selectivity of ions in an FCDI system. In this study, we demonstrated selective and continuous ion recovery by combining redox-active Prussian blue as flow electrodes and functionalized ion exchange membranes in FCDI configuration. Prussian blue selectively absorbs monovalent Na+ ions from Na+/Ca2+ mixtures through intercalation reaction, in which a smaller Stokes radius of Na+ ion is more favored to fit in the crystal lattice. Furthermore, such selectivity is much more enhanced through functionalization of a cation-exchange membrane (CEM) with polymer multilayers. A layer-by-layer method was used to deposit poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) on the CEM. Results showed that polymer multilayers changed the CEM from divalent to monovalent ion-affinity due to different ion sizes and charge density. The combination of Prussian blue and functionalized CEM raised the selectivity for sodium around 17 times compared to a control system (0.2 to 3.35). Furthermore, our results showed a highest Li selectivity of 12.88 with an extremely low energy consumption of 0.57 Wh/molLi. We believe our approach can lead to new technologies that address the shortcomings of existing lithium recycling method and expand the application not only to lithium recycling, but also to future lithium production technologies and the removal of specific ions, such as toxin removal.

Redox flow deionization using Prussian blue and functionalized ion exchange membrane for enhanced selective ion recovery

Exploring flow-electrode capacitive deionization: An overview and new insights

Brackish water was an important alternative source of freshwater. Desalination using flow electrode capacitive deionization (FCDI) needs to explore the role of ion exchange membranes (IEM) of FCDI. In this study, brackish water was desalinated using FCDI, and anion exchange membranes with different characteristics were used in the FCDI cell to investigate their influence. The result showed that the membrane polymer matrix was the main influencing factor for ion transport. Ion exchange capacity (IEC) has a huge impact that low IEC made the various ion transport priority. Low IEC not only limits ion transport but also leads to ion leakage in seawater. Resistance had a significant blockage to the effect with weak intensity.

Three-dimensional titanium mesh-based flow electrode capacitive deionization for salt separation and enrichment in high salinity water

Since flow-electrodes do not have a maximum allowable charge capacity, a high salt removal rate in flow-electrode capacitive deionization (FCDI) can be achieved theoretically by simply increasing the applied voltage. However, present attempts to run FCDI at high voltages are unsatisfactory because of the instability of the module occurring in the overlimiting current regimes. To implement FCDI in the overlimiting current regimes (namely, OLC-FCDI), in this work, we analyzed the voltage-current (V-I) characteristics of several FCDI units. We confirmed that a continuous, rapid, and stable desalination performance of OLC-FCDI can be attained when the employed FCDI unit possesses a linear V-I characteristic (only one ohmic regime), which is distinct from the three V-I regimes in electrodialysis (ohmic, limiting current, and water splitting regimes) and the two in membrane capacitive deionization (ohmic and water splitting regimes). Notably, the linearV-I characteristic of FCDI requires continuous charge percolation near the boundaries of ion-exchange membranes. Effective methods include increasing the carbon content in the flow-electrodes and introducing electrical (carbon cloth) or ionic (ion-exchange resins) conductive intermediates in the solution compartment, which result in corresponding upgraded FCDI units exhibiting extremely high salt removal rates (>100 mg m-2 s-1), good cycling stability, and rapid seawater desalination performance under typical OLC-FCDI operation condition (27-40 g L-1 NaCl, 500 mA). This study can guide future research of FCDI in terms of flow-electrode preparation and device configuration optimization.

As pressure mounts on global water systems due to climate change, growing populations, and resource constraints, the need for more sustainable and adaptive water treatment solutions is more apparent than ever. Electrified water treatment offers a compelling path forward. By using electrical energy to drive separation and redox reactions, these systems reduce dependence on chemical additives while allowing for fine control over treatment performance. Their ability to pair with renewable energy sources like solar and wind also makes them especially suitable for decentralized and off-grid settings.Among the various electrochemical methods, technologies such as electrocoagulation, electrooxidation, and electro-disinfection are gaining traction for their compact footprint and on-demand operation. In particular, Capacitive Deionization (CDI) and its advanced form, Flow-Electrode CDI (FCDI), are showing strong promise, not just for desalinating brackish water, but for tackling a much broader set of challenges. Recent developments in FCDI have pushed the boundaries of what electro-deionization can achieve. Beyond conventional desalination, FCDI has been successfully used to recover valuable resources like lithium and rare earth elements from battery leachates and acid mine drainage. It has also been applied to remove naturally occurring metals such as iron and manganese from groundwater. In some cases, FCDI has even been combined with advanced oxidation processes to create hybrid systems that handle both ionic and organic contaminants in a single step. These diverse applications highlight the flexibility of the technology and its potential to adapt to a wide range of water treatment needs.This talk will explore how FCDI is helping to shape the next generation of low-carbon, electrified water treatment systems. We will look at how it can be integrated with renewable energy, how it fits into modular and scalable treatment architectures, and how it works in synergy with other electrochemical processes. As the water sector moves toward net-zero goals, electro-deionization technologies like FCDI are emerging as key tools, offering energy efficiency, chemical reduction, and resilience in the face of today’s evolving environmental and resource challenges

Flow‐electrode capacitive deionization (FCDI) is a newly developed desalination technology with a high electrode loading for superior salt removal efficiency, even with high feed salinity. However, the improvement in FCDI performance could be restricted by obstacles such as poor charge transfer in the electrode slurry and agglomeration of the electrode particles. Therefore, various FCDI electrode materials have been studied to overcome these bottlenecks through various mechanisms. Herein, a mini‐review is conducted to summarize the relevant information and provide a comprehensive view of the progress in FCDI electrode materials. Flow‐electrode materials can be classified into three main groups: carbon materials, metal‐based materials, and carbon–metal composites. Carbon‐based capacitive materials with outstanding conductivities can facilitate charge transfer in FCDI, whereas metal‐based materials and carbon–metal composites with ion‐intercalative behaviors exhibit high ion adsorption abilities. Additionally, carbon materials with surface function groups can enhance electrode dispersion and reach a high electrode loading by electrostatic repulsion, further upgrading the conductive network of FCDI. Moreover, magnetic carbon–metal composites can be easily separated, and the salt removal performance can be improved with magnetic fields. Different electrode materials exhibit disparate features during FCDI development. Thus, combining these materials to obtain FCDI electrodes with multiple functions may be reasonable, which could be a promising direction for FCDI research.

While flow-electrode capacitive deionization (FCDI) operated in short-circuited closed cycle (SCC) mode appears to hold promise for removal of salt from brackish source waters, there has been limited investigation on the removal of other water constituents such as nitrate, fluoride or bromide in combination with salt removal. Of particular concern is the effectiveness of FCDI when ions, such as nitrate, are recognized to non-electrostatically adsorb strongly to activated carbon particles thereby potentially rendering it difficult to regenerate these particles. In this study, SCC FCDI was used to desalt source waters containing nitrate at different concentrations. Results indicate that nitrate can be removed from source waters using FCDI to concentrations <1 mg NO3-N L−1 though a lower quality target such as 10 mg L−1 would be more cost-effective, particularly where the influent nitrate concentration is high (50 mg NO3-N L−1). Although studies of the fate of nitrate in the FCDI system show that physico-chemical adsorption of nitrate to the carbon initially plays a vital role in nitrate removal, the ongoing process of nitrate removal is not significantly affected by this phenomenon with this lack of effect most likely due to the continued formation of electrical double layers enabling capacitive nitrate removal. In contrast to conventional CDI systems, constant voltage mode is shown to be more favorable in maintaining stable effluent quality in SCC FCDI because the decrease in electrical potential that occurs in constant current operation leads to a reduction in the extent of salt removal from the brackish source waters. Through periodic replacement of the electrolyte at a water recovery of 91.4%, we show that the FCDI system can achieve a continuous desalting performance with the effluent NO3-N concentration below 1 mg NO3-N L−1 at low energy consumption (~0.5 kWh m−3) but high productivity.

Improving the feasibility and applicability of flow-electrode capacitive deionization (FCDI): Review of process optimization and energy efficiency

Modeling continuous flow-electrode capacitive deionization processes with ion-exchange membranes