Capacitive Desalination Research Articles

Using crude residual glycerol as precursor of sustainable activated carbon electrodes for capacitive deionization desalination

Capacitive deionization (CDI) is a promising electrochemical technology for water desalination that can contribute to reducing water scarcity. At the same time, appropriate routes for the disposal or reuse of liquid wastes are also a major current concern. Based on the water-waste nexus concept, this work demonstrates that crude glycerol from biodiesel plants can be successfully used to obtain a new sustainable activated carbon. After polymerization, the crude glycerol was carbonized and activated to obtain polyglycerol activated carbon (PGAC), which was employed as an electrode for CDI desalination of brackish water. Evaluation was made of the electrode performance and stability over cycles of electrosorption/desorption, using different cell configurations (symmetric, asymmetric, and membrane CDI) and cell voltages (Ecell). It was observed that maintaining the potential of zero charge of the negative and positive electrodes outside their working domains during the cycles enabled minimization of that part of the applied potential deviated to co-ion repulsion, consequently improving the salt adsorption capacity (SAC) and charge efficiency (QE). Furthermore, maintaining the potential of the positive electrode below the oxidation potential by controlling the applied Ecell could ensure electrode stability. The best desalination performance using the PGAC electrode was achieved using the membrane CDI configuration (at 1.6 V), resulting in stable SAC (∼27.1 mg g−1) and QE (∼100%) over 50 cycles. The low cost and high SAC and QE values suggested that the PGAC electrode could be considered a potential candidate for use in CDI desalination.

The electrosorptive response of a carbon nanotube flow-through electrode in aqueous systems

The capture and recovery of valuable products from wastewater and/or bio-broths is one of today’s industrial challenges. Potential-controlled chromatography is a versatile solution to separate charged or polarized target species from aqueous systems. This capacitive flow-through technique combines the advantages of capacitive desalination and ion-exchange chromatography. The separation principle is controlled by system-dependent solid–liquid interaction mechanisms at the potential-controlled interface and characterized by the electrochemical double layer (EDL) formation. We conducted new experiments on the process- and environment-dependent surface effects in aqueous systems to better understand electrically driven processes inside a macroporous multi-walled carbon nanotube electrode. Here, the column and current response are investigated as a function of flow rate, as well as mobile phase pH-value, composition and concentration. Due to the strong water affinity of the material, water ions significantly co-define the EDL. The current response depends particularly on the ion properties and concentration. The use of electrolytes promotes capacitive and faradaic current and diminishes pH-deviation occurring at a negative potential. The effective range of the EDL decreases with increasing shear forces. Finally, a better performance for electrosorbing maleic acid is guaranteed at higher electrolyte concentration and low flow rate. This paper successfully addresses research gaps in potential-dependent effects that occur in multi-walled carbon nanotube electrodes.

Spinel ZnCo2O4 Electrode for Capacitive Desalination: Understanding the Enhanced Capacitive Desalination Performance of Spherical ZnCo2O4 Electrode (Adv. Mater. Interfaces 11/2021)

The ball-like spinel ZnCo2O4 (ZCO) electrode is proposed for capacitive desalination in article number 2100125 by Wei Si and Haibo Li. It exhibits prominent sodium-ion adsorption capacity, such as ultra-high specific capacity and remarkable cyclic stability. Most significantly, the desalination mechanism as well as the preferential removal behavior of Na+, K+, and Mg2+ by ZCO electrode is explored.

Enhanced capacitive deionization boosted by Co and N co-doping in carbon materials

In this study, cobalt, nitrogen co-doped porous carbon materials (Co-N/CN) as effective electrode materials were synthesized via salt melt synthesis method for capacitive desalination (CDI). The as-synthetized materials possess suitable micro/mesoporous cross-linking structure, more structure defect and multi-function groups. The systematic investigations demonstrated that Co, N codoping can promote the electrochemical performance and CDI performance. By comparison with the single N doped sample, the Co-N/CN samples achieve higher specific capacitance, lower ion/electron transport resistance and larger deionization capacity. Such superior capacitive desalination performance can be contributed to the synergistic effect of doped Co and N, such as the generation of Co-N sites. Additionally, the optimum Co-N/CN electrode displays an outstanding desalination capacity of 58.82 mg NaCl g−1 (71.4 mg Cl g−1 of anode) at 1.4 V in a NaCl concentration of 824 mg L−1 and great cycling stability with no obvious degradation in charge storage during 100 charge/discharge cycles. Therefore, we believe that Co-N/CN electrode has great potential for CDI practical applications.

Pore-scale study of capacitive charging and desalination process in porous electrodes and effects of porous structures

The capacitive deionization (CDI) involves processes of ion transport and storage within porous electrodes. A pore-scale model based on the lattice Boltzmann (LB) method is developed to study the dynamics of capacitive charging and desalination in CDI cells by considering microstructures of porous electrodes. The governing equations for mass transport and potential within the separator and pores of electrodes are derived for the case of thin electrical double layers. For the salt adsorption and charge transport between the solution and charged matrixes, the effective boundary conditions suitable for LB simulations are developed based on the Gouy-Chapman-Stern model. The transient processes of capacitive charging and desalination upon the application of a step cell voltage are revealed, and effects of potential, porosity, particle diameter and porous structure on the dynamic processes are investigated. Simulation results show that the salt removal of the separator is a diffusion limited and relatively slow process compared with the charging process of porous electrodes. The amount of equilibrium salt removal is proportional to the cell voltage and specific surface area of porous electrode. The salt removal rate is mainly affected by the effective diffusivity of porous electrode. Approaches of enhancing the effective diffusivity, such as increasing the porosity under the same particle size and enlarging the particle diameter under the same porosity, can improve the salt removal rate but reduce the salt adsorption capacity due to the decrease of specific surface area. Under the same specific surface area, the porous electrode with large pores introduced along the diffusion direction shows the highest salt removal rate without decreasing in salt adsorption capacity.

Phosphate recovery as vivianite using a flow-electrode capacitive desalination (FCDI) and fluidized bed crystallization (FBC) coupled system

It is critical to both effectively remove and recover phosphate (P) from wastewater given the wide-ranging environmental (i.e., preventing eutrophication and restoring water quality) and economic (i.e., overcoming P resource scarcity) benefits. More recently, considerable academic effort has been devoted towards harvesting P as vivianite, which can be used as a potential slow-release fertilizer and possible reagent for the manufacture of lithium iron phosphate (LiFePO4), the precursor in fabricating Li-ion secondary batteries. In this study, we propose an innovative P recovery process, in which P is first preconcentrated via a flow-electrode capacitive deionization (FCDI) device followed by immobilization as vivianite crystals in a fluidized bed crystallization (FBC) column. The effects of different operational parameters on FCDI P preconcentration performance and energy consumption are investigated. Results show that 63% of P can be removed and concentrated in the flow-electrode chamber with a reasonable energy requirement under optimal operating conditions. The FBC system resulted in immobilization of ~80% of P as triangular or quadrangular pellets, which were verified to be high-purity vivianite crystals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and extended X-ray absorption fine structure (EXAFS) spectroscopy. This study provides a pathway for efficient recovery of P as a value-added product (i.e., vivianite) from P-rich wastewaters.

Capacitive desalination of a low concentration aqueous sodium chloride solution based on a SnO2 and polystyrene co-functionalized graphene oxide electrodes

Capacitive desalination for low concentration saline water (NaCl concentration of <60 mg/L) is becoming ever more important and challenging due to its application in special circumstances, such as water purifiers in pacemakers and precision instruments for integrated circuit boards. Here, we develop SnO2 and aminated polystyrene co-functionalized graphene oxide nanocomposites (SnO2/PPAS-rGO) for the effective removal of low concentration NaCl in water. The excellent electrical and hydrophilic properties of SnO2 can effectively reduce the resistivity and improve the wettability of the entire material, making up for the disadvantage of the hydrophobicity of polymer. The introduction of the N atoms of amphiphilic zwitterionic SnO2/PPAS-rGO can improve the adsorption performance as a result of the interfacial interaction between lone-pair electrons and salt ions, and SnO2 can accelerate the charge transmission and furnish sites for activated adsorption. Polystyrene chains with the SnO2 nanoparticles can maintain the exposure of active sites by preventing the aggregation of GO sheets and inhibit the side reaction between the electrode and electrolyte, thereby guaranteeing structural stability with the aid of polytetrafluoroethylene as a binder. After optimizing the synthetic parameters, SnO2/PPAS-rGO-120 presents an ultrahigh electrosorption capacity of 8.07 mg/g at a cell voltage of 1.8 V with a flow rate of 20 mL/min in an aqueous 30.5 mg/L NaCl solution. Most importantly, SnO2/PPAS-rGO-120 shows an excellent adsorption rate (0.0014 s−1), reversibility and regeneration performance during multiple capacitive desalination processes.

MnO2 decorated porous carbon derived from Enteromorpha prolifera as flow-through electrode for dual-mode capacitive deionization

Owing to fresh-water shortage, developing highly efficient capacitive deionization (CDI) system equipped with low-cost electrodes is urgently required to process saline water to freshwater. On the other hand, Enteromorpha prolifera (EP for short, a typical bio-waste in global oceans) induced marine ecological crisis has become a serious threat to the global marine ecosystem. Aiming to kill two birds with one stone, we report the design of an EP-derived MnO2-decorated activated carbon composite (ep-AC@MnO2) as low-cost electrodes for high-performance dual-mode capacitive deionization. The as-fabricated ep-AC@MnO2 displays a high specific capacitance of 335.6 F g−1 with dual-mode sodium storage behavior. Benefiting from this unique dual-mode capacitance feature, the ep-AC@MnO2-based dual-mode CDI system exhibits highly efficient desalination performance (desalination capacity/rate: 25.7 mg g−1/2.95 mg g−1 min−1) with excellent desalination recyclability (11.3% declination after 30 cycles). This work could be of broad interest since it not only exemplifies the simple fabrication of low-cost yet high-efficiency CDI electrode material with dual-mode capacitance for capacitive desalination, but also offers a sustainable strategy to turn marine biowaste into treasure for possible relieving of the EP-induced marine ecological crisis.

Facially Synthesis of Ni(OH) &lt;sub&gt;2&lt;/sub&gt; Nanoarray on RGO@ Carbon Fabric as Dual-Functional Electrochemical Materials for Supercapacitors and Capacitive Desalination

A high performance Ni(OH)2 nanoarray on RGO@ carbon fabric nanocomposites with hierarchical nanostructures were facilely synthesized, which involves i. coating of graphene on carbon fabric; ii, in-situ growth of Ni(OH)2 nanoarray on graphene surface. It is found that Ni(OH)2 nanoplates grown evenly on the surfaces of graphene without stacking. This unique structure of electrode material favors to a higher electrochemical active sites, which endows the enhancing capacity performance. The morphology and the microstructure of the as-prepared composites were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) techniques. Capacitive properties of the synthesized electrodes were studied using cyclic voltammetry, charge/discharge, and electrochemical impedance spectroscope in a three-electrode experimental setup. Favors from the unique structure of Ni(OH)2/RGO@carbon fabric nanocomposites, this material as dual-functional electrodes shows decent performance for both supercapacitor and capacitive desalination (CDI). The specific capacitance is calculated to be 1325 F g-1 at 1 A g-1, moreover, this material shows a high rate capability, the capacitance can be maintained at 612 F g-1 even at 10 A g-1. Besides, the performance of it as potential CDI electrodes were explored. Such high-performance Ni(OH)2/RGO@carbon fabric hierarchical nanostructures can offer great promise in large-scale energy storage device applications.

Toward sustainable desalination using food waste: capacitive desalination with bread-derived electrodes.

Each year approximately 1.3 billion tons of food is either wasted or lost. One of the most wasted foods in the world is bread. The ability to reuse wasted food in another area of need, such as water scarcity, would provide a tremendous sustainable outcome. To address water scarcity, many areas of the world are now implementing desalination. One desalination technology that could benefit from food waste reuse is capacitive deionization (CDI). CDI has emerged as a powerful desalination technology that essentially only requires a pair of electrodes and a low-voltage power supply. Developing freestanding carbon electrodes from food waste could lower the overall cost of CDI systems and the environmental and economic impact from food waste. We created freestanding CDI electrodes from bread. The electrodes possessed a hierarchical pore structure that enabled both high salt adsorption capacity and one of the highest reported values for hydraulic permeability to date in a flow-through CDI system. We also developed a sustainable technique for electrode fabrication that does not require the use of common laboratory equipment and could be deployed in decentralized locations and developing countries with low-financial resources.

Highly efficient atomically dispersed Co–N active sites in porous carbon for high-performance capacitive desalination of brackish water

Carbon materials with external defects (heteroatoms) have been widely studied to promote their performance in capacitive deionization (CDI), but the salt adsorption capacity and rate capability are far from meeting the rapid demand for clean water.

Sustainable development of ultrathin porous carbon nanosheets with highly accessible defects from biomass waste for high-performance capacitive desalination

Biomass-derived defective porous carbons with numerous superiorities have received widespread attention for capacitive deionization (CDI).

Engineering of 3D NaxCoO2 nanostructures for enhanced capacitive deionization: performance and mechanism

The morphology and capacitive desalination mechanism of 3D Na0.6CoO2.

In-situ formation of uniform V2O5 nanocuboid from V2C MXene as electrodes for capacitive deionization with higher structural stability and ion diffusion ability

Capacitive desalination (CDI) has aroused much attention due to its advantages of low energy consumption and environmental compatibility. However, typical CDI processes display limited efficiency. In this work, one-dimensional V2O5 with nanocuboid structure was prepared with MXenes(V2C) precursor for the first time, which has high adsorption capacity, structure stability and fast ion diffusion ability. The as-synthesized V2O5 electrode achieved a salt adsorption capacity(SAC) of 55.2 mg NaCl g−1 V2O5 under optimized conditions with a constant current density of 30 mA g−1, a voltage range from −0.6 to 1.2 V, and an initial solution of 500 mg L−1 NaCl. Furthermore, from the comprehensive analysis of mechanism, due to the high conductivity and low charge transfer resistance of V2O5 electrode, it reduces the energy loss of the resistance during desalination. A particularly low energy consumption of 0.27 kWh kg−1-NaCl is reached when the operation is carried out successfully at low voltage range, indicating the advantages of energy saving and high efficiency. Therefore, V2O5 is an attractive and promising electrode material, which exhibits the potential of pseudocapacitive materials with certain structure for practical CDI application in future and inspires us to have a deep insight into the effect of morphology on the properties.

Sulfonated Phthalocyanine Redox Flow Cell for High-Performance Electrochemical Water Desalination

A reliable clean water supply is now one important and challenging issue for the human society. With the facts that only 0.4% of the water on earth is readily drinkable and 98% of the water is saltwater, water desalination for clean water production has become a key strategic solution to satisfy the increasing global water demand. Over the years, different saltwater desalination technologies were researched and developed, including reverse osmosis membrane desalination (RO), electrodialysis (ED), capacitive desalination (CDI) and multi-effect distillation (MED). However, some inherent technical issues, like high operation cost, large capital cost and/or low desalination capacity, associate with these existing technologies that lead to a high clean water production cost and limit their applications. Thus, there is a need of new water desalination technology that can purify saltwater with low cost and high efficiency.In this work we report a new water-soluble nickel phthalocyanine tetrasulfonic acid tetrasodium salt (NiPcTATS)-based redox flow desalination battery (RFDB) for safe, effective and efficient water-salt separation. The fabricated RFDB cell exhibited a high desalination rate at 3.4 gNaCl/(molNiPcTATS∙hr) even with a low 0.5 V cell voltage and required as low as 11.5 kJ/mol salt in energy consumption. The cell showed excellent reversibility and durability for long-term operation, benefiting from the fast-redox kinetics and chemical stability of the redox couple. With no consumption of the redox couple and energy recovery during the salination process, this new method provides a continuous desalination capability with unlimited salt removal capacity. We also demonstrated the use of simple solar panel for effectively driving the RFDB cell, proving it a promising and practical technology for clean water production in remote places like islands and ships.

Synthesis of single and bimetallic oxide-doped rGO as a possible electrode for capacitive deionization

Porous carbon doped with transition metal oxides is rapidly becoming a key research topic in capacitive deionization desalination. This work reports a simple method for the synthesis of rGO doped with different ratios of nickel and cobalt oxides, i.e., 0, 10, 15, 25, 50, 75, and 100 wt%. The nanocomposite material was prepared via a modified Hammer`s method, followed by a hydrothermal doping process. The prepared samples were characterized using the X-Ray diffractometer (XRD), scanning electron microscope, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy. TEM images revealed the arbitrary distribution of nickel and cobalt oxides in the rGO layer with an average particle size of 13 nm. The performance of the prepared materials was investigated ex situ, i.e., using a typical three-electrode cell. Also, it was verified in situ during the cell operation, i.e., using a two-electrode cell. Results showed that the performance of rGO was improved in the presence of Co3O4 and NiO nanoparticles as they form ternary Co3O4/NiO/rGO composites. Both XRD and EDX analyses confirmed the presence of Ni and Co in oxide form and attached to the rGO. The three-electrode cell measurements were from − 0.6 to 0.6 V in 1 M aqueous NaCl. The electrochemical measurements demonstrated that the rGO-25Ni, rGO-25Co, and rGO-15(50Ni-50Co) electrodes exhibited the best capacitive performance. Those samples achieved specific capacitances as high as 357 F g−1, 368.7 F g−1, and 461.5 F g−1, respectively. Such values are higher than those of electrodes based on rGO (82.77 F g−1), nickel oxide (2.98 F g−1), and cobalt oxide (3.8 F g−1). Better performance has been achieved using an equal ratio of bimetallic oxide loaded into the rGO than the single oxides or other ratios.

Hierarchical Porous Carbon for High-Performance Capacitive Desalination of Brackish Water

Capacitive deionization (CDI), as an energy-efficient and promising brackish water desalination technique, has certain advantages over conventional methods such as thermal distillation, ultrafiltra...

ELECTROSORPTION OF SALT IONS USING TITANIUM DIOXIDE-DECORATED rGO AS A PROMISING ELECTRODE CANDIDATE

Transition metal oxide (TMO) nanoparticles are particularly important in capacitive deionization desalination due to their wide areas of application. The performance of rGO decorated with TiO2 nanoparticles has been investigated. Hammer method synthesizes the electrodes, followed by a hydrothermal treatment. The morphological properties of the rGO and rGO-15TiO2 were characterized by FE-SEM and TEM measurements. The TEM images indicated the random distribution of titanium oxides in the rGO layer, while SEM images showed that the TiO2 homogeneously covered and distributed on rGO sheets for rGO-15TiO2. The performance of the prepared nanocomposite electrode's electrochemical conduct was assessed by cyclic voltammetry (CV) ex-situ. In the three-electrode system, was observed from -0.6 to 0.6 V in 1 M aqueous NaCl. The results illustrated that rGO-15(TiO2) electrode showed the best performance in the CDI, achieving the highest specific capacitance of 473.9/g at 25mV/sec. The results indicating that rGO-15TiO2 is a novel electrode material for CDI.

Synthesis of hierarchical Mn3O4 nanowires on reduced graphene oxide nanoarchitecture as effective pseudocapacitive electrodes for capacitive desalination application

We present a hierarchical network architecture fabrication of pseudocapacitive Mn3O4 nanowires immobilized on reduced graphene oxide (Mn3O4/RGO) hybrids for effective capacitive deionization (CDI). A hydrothermal synthesis process was employed for constructing Mn3O4/RGO nanoarchitecture with hierarchical pores to ease the interaction with salt ions. Physico-chemical analysis verified the Mn3O4 nanowires with few microns sized length and diameter of 20–30 nm were evenly immobilized on the surfaces of the RGO. With this tailored nanoarchitecture, the Mn3O4/RGO based electrode shows ideal pseudocapacitive behavior with a higher capacitance of (Cs) of 437 F g−1, the energy density of 41.12 Wh kg−1 and power density of 400 W kg−1 at 1 A g−1 in 1 M NaCl solution. Benefiting from the fascinating electrochemical features, the Mn3O4/RGO nanoarchitecture constructed CDI electrode exhibited high electrosorption capacity (SAC) of 34.5 mg g−1 at 1.2 V with a high salt adsorption rate (ASAR) of 1.15 mg g−1 min−1 in 1000 mg L−1 NaCl solution. The much improved SAC, ASAR, and recyclability could be attributed to the distinctive pseudocapacitive nanoarchitecture, which improves the sodiation/desodiation. The present investigation indicates that the Mn3O4/RGO nanoarchitecture is a capable CDI electrode material for desalination application.

Evaluation of capacitive deionization desalination technology for irrigation

Evaluation of capacitive deionization desalination technology for irrigation