Electrosorption Kinetics Research Articles

Dual redox centers in MnCo2O4 nanorod cathode for highly efficient capacitive deionization

Capacitive deionization (CDI) technology via faradic electrodes with active redox pairs has achieved tremendous success in desalination. However, the inner collaborative mechanisms of multi-redox centers in electrodes are rarely deep-analyzed. Thus, this work intensively investigated the inner enhanced mechanisms of multi-redox centers, starting from the dual-redox-based MnCo2O4 nanorod (MCO-NR) cathode in capacitive desalination. The electrochemical tests indicated a surface capacitive ratio of MCO-NR as high as 86 % when the scan rate was 100 mV s−1. Multi-dimensional CDI tests demonstrated that the highest capacity of MCO-NR could reach 61.78 mg g−1, with four theory models elaborating the electrosorption kinetics and maximum desalination capability. The refined ex-situ XPS measurements, carefully designed comparative experiments, and DFT calculations were used to analyze the Na+ (de)intercalation characteristics, the inner enhanced electrosorption mechanisms of dual redox centers, and the effects that the Mn redox center exerts on the MnCo2O4 structure. These results showed the superiority of dual- or multi-redox-center-based faradic capacitive desalination, providing a new perspective for designing high-property faradic electrode materials.

Electrosorption approach removing PFOA from wastewater using a MXene-polyaniline film

Perfluorooctanoic acid (PFOA) is a persistent organic pollutant found in various industrial effluents, posing significant environmental and health risks. Electrosorption of PFOA on MXene-polyaniline film from water was studied. The results of electrosorption kinetics showed that the functionalized MXene film with polyaniline resulting in an approximately 100 % increase in electrosorption capacitance for PFOA due to increasing of the MXene film's volumetric capacitance and modifying of surface chemistry of MXene. The maximum adsorption of PFOA on MXene and MXene-polyaniline films were 358.5 mg/g and 966.1 mg/g, respectively, at an initial concentration of 100 mg/L upon application of +1.0 V. Moreover, humic acid (HA) competing with the adsorption sites, sodium chloride through the double-layer compression effect, and pH affecting the amine or amide functional groups on MXene-polyaniline which inhibited PFOA adsorption onto MXene-polyaniline film were thoroughly examined. Lastly, the reversible adsorption–desorption cycles show that the MXene–polyaniline film possesses the potential to be used continuously. To address PFAS pollution in water sources, we think our approach can help build effective and long-lasting technology.

Novel malonamide-amidoxime bifunctional polymers decorated graphene oxide/chitosan electrode for enhancing electrosorptive removal of uranium(VI)

Developing the best electrode and exploring its electrosorption process are key to promoting the industrialization of uranium(VI) electrosorption. Herein, malonamide-amidoxime bifunctional polymers (MAFP) was incorporated into graphene oxide/chitosan (GO/CS) to prepare a high-performance composite electrode (MAFP/GO/CS) for U(VI) electrosorption. The as-prepared MAFP/GO/CS electrode displayed a more obvious porous structure, a larger specific surface area, an abundant amide and amidoxime group, as well as better hydrophilicity and electrochemical characteristics. This electrosorption experiment systematically examined the effects of voltage, electrosorption time, pH, and initial U(VI) concentration. According to the results, MAFP/GO/CS electrode had the maximum U(VI) electrosorption capacity of 260.58 mg/g at pH 6 and −1.2 V. It was found that Langmuir’s and pseudo-second-order kinetic models of electrosorption were well suitable for simulating the U(VI) electrosorption kinetics and isotherms. A major contribution to enhanced electrosorptive U(VI) by MAFP/GO/CS electrode could be attributed to the synergetic coordination of U(VI) by amide and amidoxime groups in MAFP moieties. This work served as a good guideline for incorporating MAFP with GO/CS to fabricate a novel electrode for U(VI) electrosorption.

Evaluation of templated N/P co-doped hierarchical mesoporous biocarbon/2D-molybdenum disulfide/polypyrrole composite as a supercapacitor electrode for U(VI) electrosorption

In this work, a templated N/P co-doped hierarchical porous biocarbon was prepared through the carbonization of sugar at high temperature (700 °C). Then, this porous biocarbon was in-situ functionalized with molybdenum disulfide nanosheets through a hydrothermal treatment reaction to get the composite, SC/MoS2. Later, SC/MoS2 on a nickel foam substrate was electrodeposited with different concentrations of polypyrrole, a conducting polymer, at −0.9 V. The prepared composite electrodes (SC/MoS2/PPy) were characterized thoroughly using FTIR, XRD, BET, and SEM. The orderly developed mesoporosity and N, P doping inside the porous carbon network was found to be highly conducive for the U(VI) electrosorption accomplished through capacitive deionization (CDI). The composites had remarkable specific capacitance (95.4 F/g), a large specific surface area (174.4–273.6 m2/g), improved mesopore volume (0.58 cm3/g) and excellent Vm/Vt ratio (0.80). SC/MoS2/PPy-2, among other composites, revealed fast electrosorption kinetics and excellent selectivity with a maximum sorption capacity of 300.66 ± 8.02 mg/g at −0.9 V. The SC/MoS2/PPy-2 retained relatively small charge transfer resistance Rct (1.22 Ω cm2), minute electrolytic resistance Rs (0.77 cm2), and a large double layer constant phase element qdl (0.0369 S sn/cm2) which makes it suitable for U(VI) ion diffusion and fast electron transfer during CDI performance. The composite electrode materials offer novel and potent desalination applications, specifically in uranium extraction from aqueous media.

The electrosorption of uranium (VI) onto the modified porous biocarbon with ammonia low-temperature plasma: Kinetics and mechanism

Constructing the excellent rich-mesoporous carbon and exploring its electrosorption process are keys to promote the electrosorption industrialization of uranium. In this work, we develop a rich-mesoporous biocarbon by using alkali-thermal-pyrolysis and ammonia low-temperature plasma, and then systematically investigate its electrosorption kinetics and mechanism of U(VI) considering a series of Faradaic side reactions. After the above treatment, the electrosorption efficiency of U(VI) onto biocarbon improves from 49.75% to 94.45%, and the ultra-high U-selectivity coefficient (SU/M) is higher than 120 from the mixed solution. The kinetic diffusion process of U(VI) into the pores is crucial, even in different water systems. Importantly, Faradaic side reactions are proved to be non-negligible factors in the electrosorption of uranium. Especially, the oxygen reduction at the cathode can convert dissolved oxygen into H2O2, which oxides the amorphous electro-reduced U(V, IV) to U(VI), and finally forms crystalline uranium peroxide species. To sum up, this work not only offers an excellent uranium-selectivity electroadsorbent, but firstly confirms the influence of Faradaic side reactions that has been ignored in the current electrosorption of uranium.

Improving the electrochemical desalination performance of chloride-doped polyaniline activated carbon electrode by tuning the synthesis method

Activated carbon obtained from chloride-doped polyaniline (PAC/Cl) is an attractive material for brackish water desalination using capacitive deionization (CDI), due to its easy synthesis, low cost, and fast electrosorption kinetics. However, its low content of surface oxygen groups (SOGs) suppresses the salt adsorption capacity (SAC), despite high specific surface area. In this work, different strategies to improve the SAC and boost the kinetics of PAC/Cl electrodes were investigated by modifying the synthesis procedure. Firstly, the use of Pluronic F127 (PLR) as a template (CTAK electrode) allowed modification of the structure and textural properties of the carbonized and activated samples, increasing the SOG content by 26 % (from 4.2 to 5.3 at.%), compared to the electrode prepared in the absence of PLR (CTAK*). Consequently, the electrode hydrophobicity was reduced by 2.1-fold (from 87.4 to 40.9°) and the desalination performance was enhanced, especially using an asymmetric electrode configuration (SAC enhancement from 11.4 to 21.0 mg g−1). Despite the slower kinetics observed using CTAK, compared to CTAK*, when the SAC and electrosorption/desorption kinetics were considered together, CTAK outperformed CTAK* by ∼ 2.0-fold (from 932 to 1560 mg g−1 day−1), in both symmetric and asymmetric configurations. As a second approach, the use of PLR combined with hydrothermal carbonization, despite leading to a 3D hierarchical framework, hindered the access to the pores, negatively impacting the process kinetics. The results showed that the use of PLR-modified PAC/Cl is a simple and effective strategy for obtaining low-cost activated carbons with distinct surface chemistry that can improve desalination performance.

Enhanced Cl– electrosorptive performance of activated carbon fibre via modification by TiO2 and polyaniline

Chloride ions in reclaimed water are the main contributors to corrosion of pipelines. In this study, titanium dioxide (TiO2)-and polyaniline (PANI)-modified activated carbon fibre (ACF) electrodes were prepared using the sol–gel method and in situ polymerisation, and their Cl– electrosorptive performance in simulated reclaimed water was extensively investigated. The prepared materials were characterised using X-ray diffraction, scanning electron microscopy, N2 adsorption, and Fourier-transform infrared spectroscopy. The experimental results indicated that the optimal Cl– removal rate from the ACF/TiO2/PANI electrode reached 85.34% when the calcination temperature of TiO2 was 400 °C and the polymerisation concentration of PANI was 0.02 mol·L−1. This study demonstrated that the ACF/TiO2/PANI electrode showed an excellent equilibrium adsorption capacity of 17.1 mg·g−1, which was 1.4 times that of the parent ACF. The superior performance was attributed to the modification of TiO2 and PANI, which considerably improved the hydrophilicity, conductivity, and physical adsorption capacity of the electrode. Consequently, the electrosorption rate and adsorption capacity were enhanced. In addition, the prepared ACF/TiO2/PANI electrode exhibited a high Cl– removal rate of 80.42% (adsorption capacity of 16.88 mg·g−1) in actual reclaimed water. Based on these results, the electrosorption kinetics and mechanism of the prepared ACF/TiO2/PANI electrode were analysed further.

Fluoride electrosorption in the presence of competing anions of environmental relevance by two activated carbons modified with La(III)

Here it is reported the electrosorption of fluoride in the presence of competing anions of environmental relevance (chloride, nitrate, sulfate, phosphate and arsenate) by two activated carbon electrodes impregnated with La(III), La-0.5% and La-1.5% (w/w %). The electrosorption kinetics were evaluated using equimolar initial concentrations (0.263 mM of each studied anion) in both binary solutions (F− vs. anion) and in a complex mixture comprising all anions simultaneously. For La-0.5%, the presence of nitrate and chloride did not significantly modify its fluoride removal (q = ∼19.25 µmol g−1), while these same anions decreased the fluoride removal of La-1.5% from 32.85 to 17.2 and 13.95 µmol g−1, for nitrate and chloride, respectively. In general, the divalent anions competed the most during the kinetics, decreasing the fluoride removal in both carbons; the lowest capacity values were 5.75 and 4 µmol g−1 for La-0.5% and La-1.5%, respectively. The increases in the pH of the solution corroborated that all anions anchored to the modified surface by a ligand-exchange mechanism involving the exposed hydroxyls from the La(III) clusters. The discussion of the results was not centered on the charge and the hydrated radius of the anions, but it was also expanded to other thermodynamic parameters that also denote selectivity, such as the hydration energies and mass-transport parameters. Electrochemical impedance spectroscopy was performed as a characterization technique in two electrolytes: 0.1 M NaF and the working solution, 0.263 mM NaF (5 ppm F− solution). The information obtained from the latter correlated the most with the electrosorption performance of the electrodes.

Electrosorption of phenolic compounds from olive mill wastewater: Mass transport consideration under a transient regime through an alginate-activated carbon fixed-bed electrode

Olive mill wastewater (OMWW) is an environmentally critical effluent, specifically due to its high content of phenolic compounds (PCs), which are hazardous due to their antimicrobial activities in water. However, their properties have good health effects at suitable doses. For the first time, the electrosorption of PCs from actual OMWW has been proposed for their possible recovery as value-added compounds, while decontaminating OMWW. A bio-sourced alginate-activated carbon (AC) fixed-bed electrode was prepared based on the reuse of olive pomace solid waste as powdered AC. At the optimal AC content (1% w/v), the internal ohmic drop voltage was lower (2.26 V) and the mass transport coefficient was higher (9.7 10−5 m s−1) along with the diffusivity (7.3 10−9 m2 s−1), which led to enhanced electrosorption rates. Afterward, an optimal electrode potential was obtained (−1.1 V vs. Ag/AgCl), while higher voltages led to faradaic reactions. Moreover, the adsorption capacity was lower (123 mg g−1) than that of electrosorption (170 mg g−1) and was even higher (307 mg g−1) with actual effluents. This was probably due to the influence of electromigration, which was confirmed by new models that could predict the electrosorption kinetics well considering mass transport and acid dissociation constants.

Flexible structural engineering of PPy-NiCo-LDH@Mxene for improved capacitive deionization and efficient hard water softening process

Capacitive deionization (CDI), as a potential desalination technology, shows the prominent advantage in processing low-concentration brackish water. However, the traditional CDI electrodes suffer from the problems like the limited salt adsorption capacity and inferior practical application in selective ion separation process. Herein, the effective-designed three-dimensional Mxene-based composite PPy-NiCo-LDH@Mxene is constructed by integrating PPy, NiCo-LDH, and Mxene together through the hydrothermal method. Particularly, the excellent conductive PPy network can greatly alleviate the restacking of Mxene and NiCo-LDH flakes and provide effective charge diffusion and transfer channels. Moreover, the Mxene substrate can strengthen the structure stability of the composite and further reinforce the total electrical conductivity of the composite material. Meanwhile, the NiCo-LDH and Mxene provide rich ion intercalation sites, contributing to the high ion storage capacity and fast electrosorption kinetics. Consequently, the PPy-NiCo-LDH@Mxene achieves the significant specific capacitance (174 F g−1), superior charging and discharging property, and enhanced electrochemical cyclic stability. The asymmetric CDI cell (AC//PPy-NiCo-LDH@Mxene) displays the prominent salt adsorption capacity (31.5 mg g−1), rapid salt removal rate (4.7 mg g−1 min−1), fast electrosorption kinetics, and stable adsorption/desorption process. Furthermore, in the multi-salt solutions with different salt solution concentrations, the PPy-NiCo-LDH@Mxene electrode displays the superb adsorption selectivity to the Ca2+ and Mg2+ than Na+, which indicates its suitable application for hard water softening process. The effective structural design exhibits huge potential for applying effective electrode materials for fast CDI process and hard water softening.

Unraveling the Ion Adsorption Kinetics in Microporous Carbon Electrodes: A Multiscale Quantum-Continuum Simulation and Experimental Approach.

Understanding sorption in porous carbon electrodes is crucial to many environmental and energy technologies, such as capacitive deionization (CDI), supercapacitor energy storage, and activated carbon filters. In each of these examples, a practical model that can describe ion electrosorption kinetics is highly desirable for accelerating material design. Here, we proposed a multiscale model to study the ion electrosorption kinetics in porous carbon electrodes by combining quantum mechanical simulations with continuum approaches. Our model integrates the Butler-Volmer (BV) equation for sorption kinetics and a continuously stirred tank reactor (CSTR) formulation with atomistic calculations of ion hydration and ion-pore interactions based on density functional theory (DFT). We validated our model experimentally by using ion mixtures in a flow-through electrode CDI device and developed an in-line UV absorption system to provide unprecedented resolution of individual ions in the separation process. We showed that the multiscale model captures unexpected experimental phenomena that cannot be explained by the traditional ion electrosorption theory. The proposed multiscale framework provides a viable approach for modeling separation processes in systems where pore sizes and ion hydration effects strongly influence the sorption kinetics, which can be leveraged to explore possible strategies for improving carbon-based and, more broadly, pore-based technologies.

New Approach for Investigating Diffusion Kinetics Within Capacitive Deionization Electrodes Using Electrochemical Impedance Spectroscopy

Capacitive deionization (CDI) has become an important research topic in terms of water purification as it is a cost- and energy efficient approach for the desalination of brackish water. Carbon- based materials are often used as electrodes in this process due to a variety of morphologies and their suitable performance in this field. In recent studies it has been already shown that a conscientiously chosen set of electrode properties has an enormous effect on the performance behavior of CDI cells. However, most of the studies focus on the optimization of the electrosorption capacity, while the question on how material properties influence the kinetic behavior of a CDI setup has been less intensively studied so far. Here we show that the kinetic effects of electrode materials can be studied in great detail by using electrochemical impedance spectroscopy (EIS). EIS studies of CDI electrodes have been reported before, however, in contrast to these we introduce a method of presenting and analyzing EIS results. This is especially suitable for extracting the frequency ranges in which different rate limiting mechanisms dominate. The new Nyquist Incline Frequency plot (NIF) shows the local slope of the Nyquist plot in dependency of the applied frequency. By this, electron transfer and mass transfer mechanisms which show a characteristic slope in the classical Nyquist plot can be directly visualized together with the information in which time domain they occur. The data derived from the new EIS plot show a clear correlation to pore size distributions from BET measurements, as well as effective capacities and electrosorption kinetics, extracted from CDI experiments. Therefore, we think that by using the NIF plot electrode materials for CDI processes can be conveniently characterized and compared within a single diagram, helping to standardize CDI material development.

Transforming waste polystyrene foam into N-doped porous carbon for capacitive energy storage and deionization applications

We have utilized cheap and readily available expanded polystyrene (EPS) foam waste as a raw material for the synthesis of a hypercrosslinked polymer. Using this polymeric scaffold, we have synthesized a series of nitrogen-doped porous carbons (PSC-3-X) via KOH activation at different temperatures. The optimized carbon material (PSC-3-700) exhibits a specific surface area of 810 m2 g−1 and optimum porosity suitable for capacitive applications such as supercapacitors and capacitive deionization. Moreover, the high nitrogen (5.23%) and oxygen (8.93%) contents present in the material enhances the electrochemical performance. PSC-3-700 exhibits the highest specific capacitance of 327 F g−1 at 1.0 A g−1 in 1 M H2SO4 aqueous electrolyte and 100% capacitance retention even after 10,000 charge–discharge cycles. It also displays a high electrosorption capacity of 34.8 mg g−1 for 500 mg L−1 NaCl solution at an applied voltage of 1.6 V in capacitive deionization application. The charge storage mechanism and electrosorption kinetics of the material have been investigated in detail.

Enhanced phosphate removal under an electric field via multiple mechanisms on MgAl-LDHs/AC composite electrode

Phosphorus removal is essential to avoid eutrophication in water bodies. Layered double hydroxides (LDHs) are widely used to scavenge phosphate through intercalated ion exchange or surface complexation. Moreover, LDHs have attracted increasing attention as electrode modifiers for supercapacitors. Researchers have begun to re-delve the electrosorption technology according to the fundamental principle of electrical double layers. Herein, we propose a new phosphate removal method inspired by the adsorption characteristic and electrical double-layer capacitive properties of LDHs through electrosorption via capacitive deionization. We present a series of experiments to study the enhanced phosphate removal under an electric field via multiple mechanisms on the MgAl-LDHs/AC electrode. The uptake of phosphate by MgAl-LDHs/AC was investigated as a function of phosphate concentration, applied voltage, electrode materials, and temperature. The MgAl-LDHs/AC electrode possessed a salt removal capacity of 67.92mg PO43−·g−1 (1.2V, 250mg·L−1 KH2PO4, 30°C). The electrosorption kinetics of phosphate ions onto the capacitive deionization electrode followed the pseudo-second-order kinetics model rather than the pseudo-first-order kinetics model. Furthermore, the adsorption isotherms of phosphate on the MgAl-LDHs/AC electrode fitted the Freundlich model better than the Langmuir model. The proposed method could be used for phosphate removal.

Equilibrium and kinetic studies of an electro-assisted lithium recovery system using lithium manganese oxide adsorbent material

This study examined the influence of operating parameters on the electrosorptive recovery system of lithium ions from aqueous solutions using a spinel-type lithium manganese oxide adsorbent electrode and investigated the electrosorption kinetics and isotherms. The results revealed that the electrosorption data of lithium ions from the lithium containing aqueous solution were well-fitted to the Langmuir isotherm at electrical potentials lower than –0.4 V and to the Freundlich isotherm at electrical potentials higher than –0.4 V. This result may due to the formation of a thicker electrical double layer on the surface of the electrode at higher electrical potentials. The results showed that the electrosorption reached equilibrium within 200 min under an electrical potential of –1.0 V, and the pseudo-second-order kinetic model was correlated with the experimental data. Moreover, the adsorption of lithium ions was dependent on pH and temperature, and the results indicate that higher pH values and lower temperatures are more suitable for the electrosorptive adsorption of lithium ions from aqueous solutions. Thermodynamic results showed that the calculated activation energy of 22.61 kJ mol–1 during the electrosorption of lithium ions onto the adsorbent electrode was primarily controlled by a physical adsorption process. The recovery of adsorbed lithium ions from the adsorbent electrode reached the desorption equilibrium within 200 min under reverse electrical potential of 3.5 V.

Perchlorate removal from brackish water by capacitive deionization: Experimental and theoretical investigations

Capacitive deionization (CDI) has attracted increasing attention over the past decade for the facile removal of ions from aqueous solutions. Nowadays, CDI is rapidly growing and evolving, and has been applied in many aspects. One important application field is water remediation, i.e., removing ionic contaminants of concern from water. Herein, we investigated the feasibility of perchlorate removal from brackish waters by batch-mode CDI technology. Effects of various operating parameters on dynamic electrosorption processes of both perchlorate and chloride were examined. Meanwhile, a one-dimensional CDI process model for dual-anions was developed to quantitatively describe the electrosorption kinetics of perchlorate and chloride, and an excellent agreement between the modeling results and the experimental data was observed. Experimental results revealed a favorably strong preferential adsorption of ClO4− over Cl− in the studied CDI system under various conditions. Moreover, only slight discrepancy between adsorption-desorption cycles was found, demonstrating the good regeneration of electrodes and operational stability of the CDI cell. Finally, the scale-up studies indicated that the CDI stack with multiple pairs of electrodes could achieve a much more superior ion removal performance than the CDI cell with only one pair of electrodes. To conclude, these results showed that the CDI system was effective for perchlorate selective removal in the presence of other major ions and had potential in treatment of perchlorate-contaminated brackish water.

Comparative study on electrosorptive behavior of NH4HF2-etched Ti3C2 and HF-etched Ti3C2 for capacitive deionization

In this work, the MXene Ti3C2 with excellent electrical conductivity is obtained by etching Ti3AlC2 with NH4HF2 solution. The electrosorption performance, the electrochemical and physicochemical properties of as-prepared Ti3C2 are characterized. The results demonstrate that NH4HF2-etched Ti3C2 possesses the better intercalation pseudo-capacity and the specific capacitance is up to 78 F∙g−1, which is an increase of 34% than HF-etched Ti3C2. In addition, the desalination capacity of NH4HF2-etched Ti3C2 enhances 35.5% than that of HF-etched Ti3C2. When the initial conductivity of NaCl is ~ 1000 μS/cm, the desalination capacity of NH4HF2-etched Ti2C3 electrode is 12.1 mg∙g−1, and the pseudo-first-order model can well describe the electrosorption kinetics of NH4HF2-etched Ti3C2 electrode. Furthermore, the regeneration performance of the NH4HF2-etched Ti3C2 electrode is excellent. This study indicates a new kind of effective electrode material to improve the desalination performance of capacitive deionization (CDI) technology.

Biomorphic microchanneled electrodes for enhanced water desalination through capacitive deionization

Abstract This work reports the preparation of rattan-derived carbon electrodes and their application in capacitive deionization technology for desalination. Desalination tests were performed with different concentrations of simulated seawater in a continuous mode with gravity as the driving force and applied voltages of 0.8 and 1.2 V. Electrosorption kinetics were performed to verify desalination of the saline solutions over time. Scanning electron microscopy revealed that the microstructure of the biomorphic carbon is composed of porous microchannels with diameters of around 300 mm, which allowed both fluid flow and ion retention. The kinetics of the electrosorption presented excellent results concerning desalination of highly concentrated solutions using low voltages.

Novel Composite Electrodes for Selective Removal of Sulfate by the Capacitive Deionization Process.

Capacitive deionization (CDI) can remove ionic contaminants from water. However, concentrations of background ions in water are usually much higher than target contaminants, and existing CDI electrodes have no designed selectivity toward specific contaminants. In this study, we demonstrate a selective CDI process tailored for removal of SO42- using activated carbon electrodes modified with a thin, quaternary amine functionalized poly(vinyl alcohol) (QPVA) coating containing submicron sized sulfate selective ion exchange resin particles. The resin/QPVA coating exhibited strong selectivity for SO42- at Cl-: SO42- concentration ratios up to 20:1 by enabling preferential transport of SO42- through the coating, but had no negative impact on the electrosorption kinetics when the coating thickness was small. The cationic nature of the coating also significantly improved the charge efficiency and consequently the total salt adsorption capacity of the electrode by 42%. The resin/QPVA coated CDI system was stable, showing highly reproducible performance in more than 50 adsorption and desorption cycles. This work suggests that addition of selective ion exchange resins on the surface of a carbon electrode could be a generally applicable approach to achieve selective removal of target ions in a CDI process.

Biowaste-Derived Carbon Electrodes for Capacitive Deionization

Capacitive Deionization (CDI) is one of the most relevant emerging desalination technologies. CDI is based on the electrosorption of salts using a pair of electrically charged porous electrodes. In this way the CDI process consists on charging (ion removal)/discharging (ion desorption) cycles using the same operational principles of the supercapacitors. Therefore, CDI cells might potentially allow to recover part of the energy consumed in the desalination process while delivering drinking water. One of the key elements in this technology are, as in the supercapacitor field, the electrodes. In accordance with this, intensive research has been conducted in order to find the best electrode candidates in terms of specific surface area (SSA), porosity, electrical conductivity, surface chemistry and optimized chemical surface charge of the electrode. The combination of these properties are expected to provide higher values of salt adsorption capacity (SAC) and average salt adsorption rate (ASAR). Moreover, it should be also remarked that one of the critical requirements in order to make CDI competitive with current desalination technologies (such as reverse osmosis or electrodialysis) is the cost of the electrode materials. In order to address this challenge, the preparation of carbon electrodes from abundant biowaste precursors was studied as a low cost and green alternative to more innovative carbon composite complex materials.In this work the authors decided to evaluate different activation treatments of a biowaste precursor in order to obtain suitable activated carbons for capacitive deionization. The different structural properties (BET SSA, pore size distribution, chemical surface groups) of the synthesized AC’s were correlated not only with their electrochemical response (specific capacitance) but also with the CDI performance (SAC, electrosorption kinetics, charge efficiency and the energy consumption).