Enhanced Desalination Performance of a Flow-Electrode Capacitive Deionization System by Adding Vanadium Redox Couples and Carbon Nanotubes

Abstract

Flow-electrode capacitive deionization (FCDI) technology can achieve continuous desalination via the electrodialysis coupling method. However, electrical energy is still highly consumed. In this work, the flow carbon nanotubes (CNTs) and vanadium redox couples are utilized as the flow electrode material together with AC to achieve the energy-saving desalination process. The V 2+ /V 3+ ions are oxidized/reduced at the positive/negative electrode chambers under the constant current applied. The ions in salt feed can be continuously removed through the electrodialysis process in a three-membrane configuration (AEM|CEM|AEM). The carbon nanotubes play double roles of both electron transporter and capacitive ion capturer together with activated carbon. Excellent electrochemical desalination can be obtained. In the current sample tests, the desalination rate can be up to 0.253 μg cm −2 s −1 , and the energy consumption of 72.62 kJ mol −1 is achievable by adding 1 wt % CNTs and 20 mM/20 mM V 2+ / V 3+ to 6.41 wt % activated carbon flow electrode at the current density 0.43 mA cm −2 . This demonstrates the possibility of low-energy desalination with the continuous process. Our study provides an efficient way to promote the FCDI desalination performance, which will contribute to the development of FCDI technology in the future.

Co/Fe3O4 nanoparticles embedded in N-doped hierarchical porous carbon derived from zeolitic imidazolate frameworks as efficient oxygen reduction electrocatalysts for zinc–air battery-based desalination

“…In order to maintain the charge balance of the catholyte and feed stream, the Na + ions move from the salt feed through the CEM to the catholyte. [60][61][62] The overall consequence shows a decrease in the concentration of the middle salt stream.…”

PEDOT:PSS‐CNT Composite Particles Overcome Contact Resistances in Slurry Electrodes for Flow‐Electrode Capacitive Deionization

“…In this context, studies have already investigated various redox-active materials for FCDI, such as quinone, vanadium, Prussian blue analogs, or iodide-based redox couples. [23][24][25][26][27][28] Other possibilities for redox-based approaches, such as the introduction of pseudocapacitive metal oxides (TiO 2 , MnO 2 , RuO 2 ) or polymeric materials (PANI, Polypyrrole) were already successfully employed in CDI applications and could be transferred to FCDI to achieve similar improvements. [29][30][31] However, although these modifications and composites could generate significant progress regarding the limitations of conventional carbon-based flow electrodes, the utilized substances are still either quite expensive or exhibit time-and labor-consuming synthesis or treatment protocols.…”

“…For FCDI applications, CNTs are mostly oxidized to counteract their inherent hydrophobicity and are dispersed as a conducting agent in conventional flow electrodes, where they act as electrical bridges between adjacent carbon particles. [ 21–23 ] Besides the addition of CNTs, composite electrodes containing a mixture of carbon‐based and redox‐active materials are investigated. These redox‐active materials extend the electrical double‐layer capacitance of carbon‐based flow electrodes by a pseudocapacitance, which results from faradaic reactions and enhances the desalination performance.…”

Regulating Surface Wettability and Charge Density of Porous Carbon Particles by In Situ Growth of Polyaniline for Constructing an Efficient Electrical Percolation Network in Flow-Electrode Capacitive Deionization

“…The desalination performance of an FCDI device largely depends on the construction of effective flow electrodes, i.e., the interconnection of suspended particles for a conductive network, the large accessible area of particles for ion adsorption, and the compatible solid/liquid interface for surface wetting and ion migration. ,, Carbon materials, such as carbon nanotubes, graphene, and activated carbon (AC), often show exceptional electrical properties and thus are widely accepted as candidates for an FCDI electrode, but the hydrophobic surface property makes them not able to easily form a uniformly dispersed aqueous slurry. ,− Well, a known fact of carbon material is that a trade-off exists between electrical conductivity and surface hydrophilicity. In other words, electrical conductivity is required for constructing an electrical network in the flow electrode, while it is often sacrificed during surface wettability treatment due to the grafting of hydrophilic groups.…”