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Membrane capacitive deionization (MCDI) is an emerging water desalination platform that is compact, electrified, and does not require high‐pressure piping. Herein, highly conductive poly(phenylene alkylene) ion‐exchange membranes (IEMs) are micropatterned with different surface geometries for MCDI. The micropatterned membranes increase the interfacial area with the liquid stream leading to a 700 mV reduction in cell voltage when operating at constant current (2 mA cm−2; 2000 ppm NaCl feed) while improving the energy normalized adsorbed salt (ENAS) value by 1.4 times. Combining the micropatterned poly(phenylene alkylene) IEMs with poly(phenylene alkylene) ionomer‐filled electrodes reduces the cell voltage by 1000 mV and improves the ENAS values by 2.3 times relative to the base case. This reduction in cell voltage allows for higher current density operation (i.e., 3–4 mA cm−2). The reduction in cell voltage is ascribed to the ameliorating ohmic resistances related to ion transport at the membrane‐process stream interface and in the carbon cloth electrode. Finally, porous ionic conductors are implemented into the spacer channel with flat and micropatterned IEM configurations and ionomer infiltrated electrodes. For the configuration with flat IEMs, the porous ionic conductor improves ENAS values across the current density regime (2–4 mA cm−2), while for micropatterned IEMs it gets improved only at 4 mA cm−2. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) has been extensively studied for fabricating ion exchange membranes. This material is of interest due to its surface‐governed charge which, combined with the interlayer distance between the GO flakes stack, offers ion selectivity. However, obtaining high‐performing membranes with high ion selectivity and low ionic resistance remains challenging. To address this issue, Al(OH)4− anions are incorporated into graphene oxide membranes to increase their spontaneous negative surface charge. The anions are successfully formed and encapsulated through a reaction with the alumina support under alkaline conditions during the membrane fabrication. A modeling of the system proves the anchoring of the Al(OH)4− anions within the GO matrix. The incorporation of these anions significantly improves the permselectivity and reduces the ionic resistance, reaching approximately 95% and 2 Ω cm2, respectively. The GO‐modified membranes also present mono‐valent selectivity, which can boost reverse electrodialysis power densities. [ABSTRACT FROM AUTHOR]

Membrane based separation technologies are expanding globally to meet the demand of fresh water. Considering the perspective, this review paper summarizes the state of art of different Ion-exchange membranes (IEMs) with varying functional groups, materials, and their mode of synthesis to understand their influence in overall separation efficiency processes. Herein, the fundamental aspects of membrane phenomena with its selectivity for different counter and co-ions have been discussed in detail. Emphasis on membrane types and their synthesis parameters (i.e., loading capacity, aspect ratio of materials, filler size, filler agglomeration, and polymer-filler interaction) are being made. Lastly, the various applications of the membrane along with the basic design and challenges are discussed for longer lifetime of membrane. Thus, a profound understanding of the membrane phenomena, its attached ionic groups and interfacial properties would further help to explore the membrane-based technologies.

The aim of this study is to show the optimal arrangement of a measurement system for estimating the thermal conductivity of thin films from temperature profiles. For this purpose, two different experimental setup systems, with square and circular cross sections, were designed to estimate the thermal conductivity of thin films and, in particular, of two ion exchange membranes. Both systems were placed horizontally and vertically in order to evaluate the best orientation to more accurately determine thermal conductivity. A three-dimensional numerical simulation was performed using Comsol Multiphysics to predict the heat flow and temperature gradient and to evaluate the effect of the geometry and the orientation on the contact resistances. Each system was first calibrated without the membrane inside in order to estimate all the necessary thermal properties of the different materials of the model. Next, the membrane was placed inside the model, so that the model now includes the thermal conductivity of the membrane as the only unknown parameter. The numerical results were compared with the various measured temperature profiles to estimate the thermal conductivity. The thermal conductivity values of the well-known Nafion 117 membrane and other thicker membrane were determined. A very good agreement with reliable literature values was obtained. The approach presented here, combining experimental and simulated temperature profiles, may provide the basis for a practical alternative to better estimate the thermal conductivity of thin films. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) has been extensively studied for fabricating ion exchange membranes. This material is of interest due to its surface‐governed charge which, combined with the interlayer distance between the GO flakes stack, offers ion selectivity. However, obtaining high‐performing membranes with high ion selectivity and low ionic resistance remains challenging. To address this issue, Al(OH)4− anions are incorporated into graphene oxide membranes to increase their spontaneous negative surface charge. The anions are successfully formed and encapsulated through a reaction with the alumina support under alkaline conditions during the membrane fabrication. A modeling of the system proves the anchoring of the Al(OH)4− anions within the GO matrix. The incorporation of these anions significantly improves the permselectivity and reduces the ionic resistance, reaching approximately 95% and 2 Ω cm2, respectively. The GO‐modified membranes also present mono‐valent selectivity, which can boost reverse electrodialysis power densities.

Membrane capacitive deionization (MCDI) is an emerging water desalination platform that is compact, electrified, and does not require high‐pressure piping. Herein, highly conductive poly(phenylene alkylene) ion‐exchange membranes (IEMs) are micropatterned with different surface geometries for MCDI. The micropatterned membranes increase the interfacial area with the liquid stream leading to a 700 mV reduction in cell voltage when operating at constant current (2 mA cm−2; 2000 ppm NaCl feed) while improving the energy normalized adsorbed salt (ENAS) value by 1.4 times. Combining the micropatterned poly(phenylene alkylene) IEMs with poly(phenylene alkylene) ionomer‐filled electrodes reduces the cell voltage by 1000 mV and improves the ENAS values by 2.3 times relative to the base case. This reduction in cell voltage allows for higher current density operation (i.e., 3–4 mA cm−2) . The reduction in cell voltage is ascribed to the ameliorating ohmic resistances related to ion transport at the membrane‐process stream interface and in the carbon cloth electrode. Finally, porous ionic conductors are implemented into the spacer channel with flat and micropatterned IEM configurations and ionomer infiltrated electrodes. For the configuration with flat IEMs, the porous ionic conductor improves ENAS values across the current density regime (2–4 mA cm−2), while for micropatterned IEMs it gets improved only at 4 mA cm−2.

Polymer nanocomposite materials with catalytic activity were designed via modification of MF-4SK ion-exchange membranes with Au and Ag nanoparticles obtained according to various synthetic methods in reverse micellar solutions. A sufficient transparency of the films allowed us to detect nanoparticles in the films using UV–Vis spectrophotometry, monitoring changes in the content of metal nanoparticles in the reverse micellar solution. A different mechanism of interaction of Au and Ag nanoparticles obtained by the same synthetic method with the MF-4SK film upon their contact with its surface was discovered, the destruction of nanoparticles was observed, and the influence of mechanism of primary acts in the formation of metal nanoparticles in reverse micellar solutions on their adsorption properties was confirmed. The highest concentration of gold nanoparticles was found in films immersed in reverse micellar solutions at the time of their exposure to ionizing radiation. [ABSTRACT FROM AUTHOR]

Since the electrolyte in an iron chrome redox flow battery (ICRFB) is inexpensive, the cost of the separator can contribute up to 38% of the CapEx cost of an ICRFB. Since the membrane also influences the RFB performance, it is the aim of this study to screen various commercial ion‐exchange membranes (IEMs) and a microporous separator (MPS) in an ICRFB to identify possible alternative membranes to the currently used Nafion. The suitability of six cation (CEMs) and two anion exchange membranes (AEMs), as well as one MPS, is investigated. No discharge curves are attained with either of the AEMs, which probably result from the formation of an anionic FeCl4− species at the elevated operating temperatures (65 °C) used, confirming literature on the unsuitability of AEMs for ICRFBs. Similarly, although the MPS is stable in the ICRFB electrolyte, it yields a high capacity decay ascribed to excessive crossover. Whereas all six CEMs yield similar CE, VE, and EE values, the fumatech FS‐950 yields a comparable capacity decay but higher EE and capacity discharge than the currently used Nafion 117 counterpart. Due to the significant cost reduction, modified or customized MPS should be further evaluated. [ABSTRACT FROM AUTHOR]

Since the electrolyte in an iron chrome redox flow battery (ICRFB) is inexpensive, the cost of the separator can contribute up to 38% of the CapEx cost of an ICRFB. Since the membrane also influences the RFB performance, it is the aim of this study to screen various commercial ion‐exchange membranes (IEMs) and a microporous separator (MPS) in an ICRFB to identify possible alternative membranes to the currently used Nafion. The suitability of six cation (CEMs) and two anion exchange membranes (AEMs), as well as one MPS, is investigated. No discharge curves are attained with either of the AEMs, which probably result from the formation of an anionic FeCl4− species at the elevated operating temperatures (65 °C) used, confirming literature on the unsuitability of AEMs for ICRFBs. Similarly, although the MPS is stable in the ICRFB electrolyte, it yields a high capacity decay ascribed to excessive crossover. Whereas all six CEMs yield similar CE, VE, and EE values, the fumatech FS‐950 yields a comparable capacity decay but higher EE and capacity discharge than the currently used Nafion 117 counterpart. Due to the significant cost reduction, modified or customized MPS should be further evaluated.

This work aims to theoretically investigate the effect of both the fixed charge density of ion exchange membranes and the ionic strength of the treated aqueous NaCl solution on the generated Donnan potential at thermodynamic equilibrium conditions. The direct objective of our work is to calculate the equilibrium concentration of the Cl− co-ion inside a swelled cation-exchange membrane equilibrated with a water/NaCl system. Two activity coefficient models are employed, i.e., the Debye–Huckel (DH) model (as a reference model) and the Meissner model, which is known for its applicability in treating concentrated solutions. Experimental data available in the literature for Donnan potential are used to verify model predictions. Our study confirms that a high fixed charge density is required to counterbalance the deterioration in membrane selectivity encountered in high-salinity systems. The DH model can be safely used to predict the Donnan potential for feed compositions up to 0.1 M. At higher compositions, the DH model significantly overestimates the predicted (absolute) Donnan potential compared to the Meissner model. The osmotic pressure resulting from the difference in ionic concentration between the membrane phase and the feed phase is found to have insignificant effects on the Donnan potential. The equilibrium computations and methodology are presented in a general way that enables handling multivalent electrolyte systems such as CaCl2. [ABSTRACT FROM AUTHOR]

For the first time, based on the joint application of the fine-porous and cell models, a theoretical analysis of the changing transport and structural characteristics of heterogeneous polymeric ion-exchange membranes (IEMs) MK-40, MA-40, and MA-41 after exposure to elevated temperatures in water and aggressive media (H2SO4 and NaOH solutions), as well as after long-term processing in electrodialyzers of various types, was carried out. The studied membranes are composites of ion-exchange polymers with polyethylene and nylon reinforcing mesh. The external influences provoke the aging of IEMs and the deterioration of their characteristics. The transport properties of IEMs are quantitatively described using five physicochemical parameters: counterion diffusion and equilibrium distribution coefficients in the membrane, characteristic exchange capacity, which depends on the microporosity of ion-exchanger particles, and macroscopic porosity at a known exchange capacity of IEMs. Calculations of the physicochemical parameters of the membranes were performed according to a specially developed fitting technique using the experimental concentration dependences of integral diffusion permeability and specific electrical conductivity, and their model analogs. This made it possible to identify and evaluate changes in the membrane micro- and macrostructure and examine the process of artificial aging of the IEM polymer material due to the abovementioned external impacts. [ABSTRACT FROM AUTHOR]

The high concentration of chloride ions in desulphurization wastewater is the primary limiting factor for its reusability. Monovalent anion selective electrodialysis (S-ED) enables the selective removal of chloride ions, thereby facilitating the reuse of desulfurization wastewater. In this study, different concentrations of NaCl and Na2SO4 were used to simulate different softened desulfurization wastewater. The effects of current density and NaCl and Na2SO4 concentration on ion flux, permselectivity (PSO42−Cl−) and specific energy consumption were studied. The results show that Selemion ASA membrane exhibits excellent permselectivity for Cl− and SO42−, with a significantly lower flux observed for SO42− compared to Cl−. Current density exerts a significant influence on ion flux; as the current density increases, the flux of SO42− also increases but at a lower rate than that of Cl−, resulting in an increase in permselectivity. When the current density reaches 25 mA/cm2, the permselectivity reaches a maximum of 50.4. The increase in NaCl concentration leads to a decrease in the SO42− flux; however, the permselectivity is reduced due to the elevated Cl−/SO42− ratio. The SO42− flux increases with the increase in Na2SO4 concentration, while the permselectivity increases with the decrease in Cl−/SO42− ratio.

Industrial waste with high salinity cannot be drained into waterways due to tightened environmental regulations. Bipolar membrane electrodialysis (BPED) is getting more attraction not only to treat water flows but also to produce valuable commodities. The BPED technique has various advantages in terms of product purity, control over product concentration, having no by-products, low environmental impact, and low energy consumption. In this short paper, we emphasize a comparative study in two different configurations for the treatment of green liquor (a waste solution of NaOH, Na2S and Na2CO3 from pulp mills) with BPED to produce NaOH. The best results are obtained in a five-compartment setup where the capture of H2S formed from green liquor is possible, followed by the capture of CO2. This work also indicates that BPED technology is a sustainable solution to treat carbonate-rich waste, which will facilitate the current need to control greenhouse emissions.

Ion-exchange membranes (IEMs) are utilized in numerous established, emergent, and emerging applications for water, energy, and the environment. This article reviews the five different types of IEM selectivity, namely charge, valence, specific ion, ion/solvent, and ion/uncharged solute selectivities. Technological pathways to advance the selectivities through the sorption and migration mechanisms of transport in IEM are critically analyzed. Because of the underlying principles governing transport, efforts to enhance selectivity by tuning the membrane structural and chemical properties are almost always accompanied by a concomitant decline in permeability of the desired ion. Suppressing the undesired crossover of solvent and neutral species is crucial to realize the practical implementation of several technologies, including bioelectrochemical systems, hypersaline electrodialysis desalination, fuel cells, and redox flow batteries, but the ion/solvent and ion/uncharged solute selectivities are relatively understudied, compared to the ion/ion selectivities. Deepening fundamental understanding of the transport phenomena, specifically the factors underpinning structure-property-performance relationships, will be vital to guide the informed development of more selective IEMs. Innovations in material and membrane design offer opportunities to utilize ion discrimination mechanisms that are radically different from conventional IEMs and potentially depart from the putative permeability-selectivity tradeoff. Advancements in IEM selectivity can contribute to meeting the aqueous separation needs of water, energy, and environmental challenges. [ABSTRACT FROM AUTHOR]

A series of proton exchange electrolytes were synthesized by blending polystyrene sulfonic acid (PSSA) functionalized ZWP ion exchanger and sulfonated poly(vinylidene fluoride) (SPVDF) as base by using solution casting method. The poly(vinylidene fluoride) was sulfonated by employing a direct sulfonation technique demonstrated in the literature. Surface modification of the ZWP was done to obtain the PSSA-ZWP ion exchanger. The membranes were synthesized by using ZWP and PSSA-ZWP as ion exchangers in the SPVDF polymer matrix. The physicochemical characterization of the membranes was performed by using FT-IR and XRD. The scanning electron microscope (SEM) was used to investigate the surface morphology of the fabricated membranes for any possible defects. Important membrane parameters, such as water uptake (up to 26%), methanol uptake (up to 22%), chemical stability (7.4%) and mechanical stability (tensile strength of up to 44 MPa), were measured and are reported. The ion exchange capacity (max 0.62 meq g−1) and electrochemical characterization of the membranes was conducted and parameters such as transport number (max 0.84) indicating good ion selectivity of the membranes and proton conductivity (max 3.89 mS/cm) were also determined. The single cell DMFC performance of the SPVDF-ZWP-PSSA membrane was evaluated at three different operating temperatures of 30 °C, 60 °C and 90 °C, out of which the synthesized membrane performed best at 60 °C with maximum current density and power density of 49.8 mAcm−2 and 20.1 mWcm−2 respectively. • SPVDF based composite PEMs were fabricated using ZWP & ZWP-PSSA as ion-exchanger. • Water uptake and methanol uptake results are comparable to Nafion 117. • PEM showed good mechanical stability of 44 MPa and good chemical stability. • Transport no. of 0.84, IEC of 0.62 meq g−1 & conductivity of 3.8 mS/cm were obtained. • Current density of 49.87 mA/cm2 & power density of 20.1 mW/cm2 obtained at 60 °C. [ABSTRACT FROM AUTHOR]

The global temperature increase must be limited to below 1.5 °C to alleviate the worst effects of climate change. Electrocatalytic CO2 reduction (ECO2R) to generate chemicals and feedstocks is considered one of the most promising technologies to cut CO2 emission at an industrial level. However, despite decades of studies, advances at the laboratory scale have not yet led to high industrial deployment rates. This Review discusses practical challenges in the industrial chain that hamper the scaling‐up deployment of the ECO2R technology. Faradaic efficiencies (FEs) of about 100 % and current densities above 200 mA cm−2 have been achieved for the ECO2R to CO/HCOOH, and the stability of the electrolysis system has been prolonged to 2000 h. For ECO2R to C2H4, the maximum FE is over 80 %, and the highest current density has reached the A cm−2 level. Thus, it is believed that ECO2R may have reached the stage for scale‐up. We aim to provide insights that can accelerate the development of the ECO2R technology. [ABSTRACT FROM AUTHOR]

Heterogeneous membranes are generally prepared by mixing ion-exchange (IE) resins, whether cation or anion resins, with a polymer matrix, in which the resin is well embedded within the polymer in a homogeneous manner. In the present paper, novel membranes were fabricated and different variables were investigated, such as types of polymer matrix whether cellulose acetate (CA) or cellulose acetate butyrate (CAB), source (properties) of CA, de-esterified membranes, type of IE resins (cationic, anionic, or nonionic), and ground or pristine resins. It was found that ground resins gave thinner membranes with better perm-selectivity for both cationic and anionic IE resins with the two brands of CA tested. The nonionic IE resin gave adverse results as expected, especially when it was pulverized before mixing with the polymers. CAB gave unfavorable results compared with the two types of CA polymers studied and gave lower perm-selectivity especially when the IE resins were ground before mixing to the CAB polymer. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs) based on aqueous organic electrolytes are a promising technology for safe and cost‐effective large‐scale electrical energy storage. Membrane separators are a key component in RFBs, allowing fast conduction of charge‐carrier ions but minimizing the cross‐over of redox‐active species. Here, we report the molecular engineering of amidoxime‐functionalized Polymers of Intrinsic Microporosity (AO‐PIMs) by tuning their polymer chain topology and pore architecture to optimize membrane ion transport functions. AO‐PIM membranes are integrated with three emerging aqueous organic flow battery chemistries, and the synergetic integration of ion‐selective membranes with molecular engineered organic molecules in neutral‐pH electrolytes leads to significantly enhanced cycling stability. [ABSTRACT FROM AUTHOR]

The reverse electrodialysis heat engine (REDHE) is a promising salinity gradient energy technology, capable of producing hydrogen with an input of waste heat at temperatures below 100 °C. A salinity gradient drives water electrolysis in the reverse electrodialysis (RED) cell, and spent solutions are regenerated using waste heat in a precipitation or evaporation unit. This work presents a non-equilibrium thermodynamics model for the RED cell, and the hydrogen production is investigated for KCl/water solutions. The results show that the evaporation concept requires 40 times less waste heat and produces three times more hydrogen than the precipitation concept. With commercial evaporation technology, a system efficiency of 2% is obtained, with a hydrogen production rate of 0.38 g H 2 m − 2 h − 1 and a waste heat requirement of 1.7 kWh g H 2 − 1 . The water transference coefficient and the salt diffusion coefficient are identified as membrane properties with a large negative impact on hydrogen production and system efficiency. Each unit of the water transference coefficient in the range t w = [ 0 – 10 ] causes a −7 mV decrease in unit cell electric potential, and a −0.3% decrease in system efficiency. Increasing the membrane salt diffusion coefficient from 10 − 12 to 10 − 11 leads to the system efficiency decreasing from 2% to 0.6%. [ABSTRACT FROM AUTHOR]

• Ionomer and various polymers blended to successfully obtain AEMs. • Focus on exploring alternative polymers to PVDF. • In electrodialysis, nitrate over chloride selectivity: PVC > PVDF > PAN. • Selectivity governed by hydrophobicity and fixed charge concentration. Selective separation of monovalent ions such as nitrate from chloride using Anion-Exchange Membranes (AEMs) is challenging. Previously, we showed that an increased polyvinylidene fluoride (PVDF) concentration in AEMs manufactured with an anion-exchange ionomer solution (Fumion FAS-24) increased nitrate over chloride selectivity. The membrane containing 50 wt% of PVDF showed higher selectivity compared to two commercial membranes (AMX and ACS from Neosepta) when tested in electrodialysis. This improved selectivity was associated with increased hydrophobicity of the membrane, facilitating the permeation of less hydrated ions such as nitrate. However, due to concerns regarding per- and polyfluoroalkyl substances (PFAS), there is a quest for substitutes for fluoropolymers. In this study, we investigated whether using alternative polymers to PVDF influences nitrate/chloride separation performance. Polyvinyl chloride (PVC) and polyacrylonitrile (PAN) were blended with Fumion FAS-24 to manufacture new AEMs. The nitrate/chloride selective separation performance of these membranes was tested in electrodialysis and compared with the recently introduced PVDF-based AEM. Results show that although the PVDF-based membrane presents higher hydrophobicity, the PAN-based membrane possesses slightly lower selectivity, while the PVC-based membrane exhibits higher nitrate selectivity. This study proves that increasing the membrane hydrophobicity is a valid strategy to increase selectivity toward nitrate. However, it also suggests that other parameters, such as fixed charge concentration, can play a role. Therefore, balancing properties such as hydrophobicity and fixed charge concentration is imperative to achieving optimal selectivity and performance when developing ion-selective membranes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soft ZTC is a promising electrode material for both CDI and CapMix techniques. • Polyelectrolyte-coated ZTC enhances CDI: high salt adsorption with low energy cost. • Soft ZTC electrodes are used for the first time in energy generation by salinity exchange. • Soft ZTC electrodes with IEMs minimize leakages and maximize energy harvesting in CapMix. As global demands for freshwater and renewable energy intensify, capacitive deionization (CDI) emerges as a promising technique for water purification, desalination, and ionic separation. Reciprocally, energy harvesting has been made possible from exchanging solutions with different salinity, using the so-called capacitive mixing (CapMix) methods, now taking their first steps towards a wider range of application. In all the techniques mentioned, porous electrodes are used in order to maximize the stored charge, making it essential to properly select the material of which the electrode is composed. This work focuses on exploring the performance of zeolite-templated carbon (ZTC) as a highly promising electrode material. ZTC offers ordered pore distribution and high electrical conductivity, making it in principle ideal for energy harvesting and water purification applications. In order to optimize its performance, the surface of the ZTC is for the first time modified by application of polyelectrolyte coatings, resulting in so-called soft electrodes or SEs. This combination of electrode material and functionalization gives rise to a highly efficient and low energy-consuming strategy to fully realize the potential of this carbon material in CDI and CapMix techniques for tackling global freshwater and energy challenges. Energy and power generation values up to 25 mJ and 7.5 mW m−2 have been obtained (with measured potential rises of 131 mV by only exchanging salinities of the bathing solution), which overcome values such as 4.3 mW m−2 previously found in our laboratory under similar conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] To improve the selectivity of cation-exchange membranes to the transfer of lithium with respect to magnesium during the electrodialysis desalination of lithium and magnesium sulfates solutions, the surface of a commercial cation-exchange membrane based on sulfated polystyrene was modified with cerium(III, IV) and zirconium phosphates. Upon incorporation of phosphate particles, the Li/Mg selectivity coefficients of the membranes increased up to 113%. [ABSTRACT FROM AUTHOR]

The possible effects of ionizing radiation on four commercial membranes, which are typically used as electrolytes in fuel cells supplying energy to a huge variety of medical implantable devices, were studied. These devices could obtain energy from the biological environment through a glucose fuel cell, which could be a good candidate to replace conventional batteries as a power source. In these applications, materials with high radiation stability for the fuel cell elements would be disabled. The polymeric membrane is one of the key elements in fuel cells. Membrane swelling properties are very important because they affect the fuel cell’s performance. For this reason, the swelling behaviors of various samples of each membrane irradiated with different doses were analyzed. Each sample was irradiated with a typical dose of a conventional radiotherapy treatment, and the regular conditions of the biological working environment were simulated. The target was to examine the possible effect of the received radiation on the membranes. The results show that the ionizing radiation influenced their swelling properties, as well as that dimensional changes were dependent on the existence of reinforcement, be it internal or external, in the membrane structure.

Layer-by-layer (LBL) adsorption of polyelectrolyte multilayers (PEMs) of ion-exchange membranes (IEMs) gives rise to remarkable selectivities, however, these high selectivities are accompanied by lower fluxes of the ions, lower values of limiting currents and hence the lower rates of recoveries of the ions of interest. In this study, the charge of LBL deposited PEMs on membranes was varied to determine the effect of the charge of PEMs on water splitting, fluxes of ions and the current efficiencies. It was noticed that when a cation-exchange layer (CEL) is present on an anion-exchange membrane (AEM), a bipolar junction was created that catalyzes the process of water splitting and hence potentially decreases the limiting current values. However, the presence of a CEL on a cation-exchange membrane (CEM) significantly increases the fluxes of ions of interest and hence their rates of recoveries while still achieving an order of magnitude higher selectivities than those achieved through bare CEMs. A change in pH of the surrounding solutions from 6.5 to 8.3 creates a negative charge in the PEMs. A negative charge in the PEMs was also created by using Fe3+ ions in the polyelectrolyte solutions where Fe3+ ions were subsequently removed from the assembled PEMs. To measure the ion-exchange features of the PEMs, transmembrane potentials through the PEMs and the membranes were measured. The current-voltage curves were measured to study the water splitting through coated membrane and fluxes under different conditions were measured in diffusion dialysis, Donnan dialysis and electrodialysis. This study can greatly prove useful in relating the charge of the PEMs deposited on IEMs to the process of water splitting, ions fluxes, limiting currents and the current efficiencies. [Display omitted] • Negatively charged PEMs can be created by adding Fe3+ in the polyelectrolyte solutions • The negative charge of the PAH/PSS-films increases appreciably by raising the pH to 8.3 • A bipolar junction is generated by depositing negatively charged PEMs on AEMs • PEMs with a negative charge are more selective for Cl- /SO4 2- and show comparatively very low Na+ /Mg2+separations • The fluxes of cations increase manifold through CEMs coated with cation-exchange films [ABSTRACT FROM AUTHOR]

[Display omitted] • Detailed analysis of electrodialysis in modern chemical engineering; • In-depth review of ion transport and membrane technologies; • Scaling from lab to pilot scale challenges, including modeling of multiphysics; • Comprehensive coverage of electrodialysis in various industries; • Emerging technological innovations. This review article comprehensively explores the significant advancements in electrodialysis (ED) technology within the field of chemical engineering, presenting a holistic overview that spans fundamental principles, membrane materials and fabrication techniques, operational parameters, and a wide array of applications. Unlike previous studies that often narrow their focus to specific aspects of ED, this work synthesizes global advances, bridging gaps between diverse research themes to offer a coherent understanding of current trends and future directions. ED, a membrane-based separation process driven by electric potential, is pivotal for its applications in water purification, desalination, resource recovery, and beyond. This review delves into the evolution of ion-exchange membranes, highlighting innovations in materials, alongside advances in fabrication techniques that enhance membrane selectivity and efficiency. It also scrutinizes the impact of operational parameters on the performance of ED systems, addressing challenges like ion leakage, membrane fouling, and the balance between selectivity and conductivity. Process intensification and system optimization strategies are discussed, revealing how recent developments contribute to energy efficiency, scalability, and sustainability. The review further extends to emerging applications of ED in sectors ranging from environmental management to energy and hydrometallurgy industries, underscored by case studies that demonstrate practical implementations. Conclusively, this article underlines the multidisciplinary approach required for the advancement of ED technologies, suggesting avenues for future research that prioritize environmental impact, economic feasibility, and technological innovation. Through this global perspective, it aims to catalyze further exploration and application of ED in addressing some of the most pressing challenges. [ABSTRACT FROM AUTHOR]

Ionic diffusion coefficients in the membrane are needed for the modelling of ion transport in ion‐exchange membranes (IEMs) with the Nernst‐Planck equation. We have determined the ionic diffusion coefficients of Na+, OH−, H+, Cl−, SO42−, NaSO4−, and HSO4− from the diffusion experiments of dilute NaCl, NaOH, HCl, Na2SO4, and H2SO4 solutions through IEMs and the membrane conductivity measured in these solutions, using electrochemical impedance spectroscopy. The order of diffusion fluxes across the anion‐exchange membrane is found to be as H2SO4>HCl>NaCl>Na2SO4>NaOH, whereas for the cation‐exchange membrane it was NaOH>NaCl>Na2SO4≥H2SO4. Special attention is given to sulfates because of the partial dissociation of bisulfate and NaSO4−, which makes the use of the Nernst‐Hartley equation, that is, splitting the electrolyte diffusion coefficient into its ionic contributions, impossible. The expression of the diffusion coefficient of sulfates taking into account the dissociation equilibrium has been derived and the corresponding Fick equation has been integrated. In addition, for sulfates, finite element simulations with COMSOL Multiphysics, applying a homogeneous membrane model, were done to give estimates of their ionic diffusion coefficients. This work offers a convenient approach to finding diffusion coefficients of various ions inside IEMs. [ABSTRACT FROM AUTHOR]

Purpose: Plant species diversity is expected to affect multiple ecosystem functions, such as soil nitrogen (N) availability. However, this effect may be related to the ecological differentiation between coexisting species, often expressed as either functional diversity (FD; diversity in traits) or phylogenetic diversity (PD; diversity in phylogenetic ancestry) within plant communities. Evidence for the independent and combined role of FD and PD on ecosystem functions is generally missing, as measures of FD and PD are usually confounded in empirical studies. Methods: To solve this challenge we used an ad-hoc designed biodiversity experiment, with sown meadow plant communities forming independent combinations of FD and PD (low/low, low/high, high/low, high/high values, plus monocultures) and used ion-exchange membranes to monitor changes in soil N (i.e. NH4+-N and NO3−-N) availability through time (four sampling times per year; i.e. seasonality). Results: Our results showed a positive diversity effect for soil NH4+-N, with mixture communities yielding higher levels of NH4+-N than the corresponding monocultures. Within mixtures, communities with combinations of both high FD and PD showed the highest NH4+-N availability. Most importantly, although seasonality strongly affected soil N availability, diversity effects were generally consistent through time in the case of NH4+-N. In addition to these diversity effects, communities with higher proportion of nitrogen-fixing species also showed higher soil N availability. Conclusions: Plant communities composed of species with larger ecological differences can sustain high levels of available NH4+-N throughout the year, suggesting a stimulation of decomposition processes via the coexistence of plants with multiple strategies. [ABSTRACT FROM AUTHOR]

Al2O3/chitosan-multiwall carbon nanotubes (MWCNTs) were created to increase the exchange capacity of polyvinylidene fluoride (PVDF) ion-exchange membranes. The composite membranes were made by mixing Al2O3 nanoparticles into the PVDF cast solution, then applying a thin coating of chitosan functionalized carbon nano tubes (Cs-MWCNTs) to the PVDF membrane surface. The structure and characteristics of the hybrid membranes were described using XRD, SEM, IR, and TG-DTA. The Al2O3-PVDF/Cs-MWCNTs membrane beat the other Al2O3-PVDF/Cs, Al2O3-PVDF, and PVDF membranes in terms of molybdate, phosphate, and nitrate adsorption. The removal efficiency, pH solution, adsorption capacity, and desorption process of molybdate, phosphate, and nitrate anions by Al2O3-PVDF and PVDF membranes were investigated. The removal effectiveness of molybdate, phosphate, and nitrate, according to the testing findings, was 94.3, 65.6, and 85.78 %, respectively. The adsorption of MoO42−, PO43−, and NO3− increased as the pH increased initially until the best adsorption was achieved, and then decreased significantly as the pH increased further. The total adsorption capabilities of MoO42−, PO43−, and NO3−for the Al2O3-PVDF/Cs-MWCNTs membrane were 65.50, 61.22, and 59.77 mg/g, respectively. Using regeneration and reuse experiments for the simultaneous adsorption of molybdate, phosphate, and nitrate during three consecutive cycles, the adsorption/desorption of Al2O3-PVDF/Cs-MWCNTs was assessed. Al2O3-PVDF/Cs-MWCNTs offer a lot of promise when it comes to eliminating MoO42−, PO43−, and NO3−from actual wastewater samples.

Recycling spent lithium-ion batteries offers a sustainable solution to reduce ecological degradation from mining and mitigate raw material shortages and price volatility. This study investigates using electrodialysis with selective and bipolar ion-exchange membranes to establish a circular economy for lithium-ion batteries. An experimental data set of over 1700 ion concentration measurements across five current densities, two solution compositions, and three pH levels supports the techno-economic analysis. Selective electrodialysis (SED) isolates lithium ions from battery leachates, yielding a 99% Li-pure retentate with 68.8% lithium retention, achieving relative ionic fluxes up to 2.41 for Li + over transition metal cations and a selectivity of 5.64 over monovalent cations. Bipolar membrane electrodialysis (BMED) converts LiCl into high-purity LiOH and HCl, essential for battery remanufacturing and reducing acid consumption via acid recycling. High current densities reduce ion leakage, achieving lithium leakage as low as 0.03%, though hydronium and hydroxide leakage in BMED remains high at 11-20%. Our analysis projects LiOH production costs between USD 1.1 and 3.6 per kilogram, significantly lower than current prices. Optimal SED and BMED conditions are identified, emphasizing the need to control proton transport in BMED and improve cobalt-lithium separation in SED to enhance cost efficiency.

Novel ion-exchange membranes based on a commercial porous polytetrafluoroethylene film and sulfonated polystyrene are synthesized. To form porous polytetrafluoroethylene–polystyrene composites, thermal polymerization of styrene sorbed in the pores of the matrix-film from the monomer solution is used. The use of porous matrix makes it possible effectively obtaining the composites, used as precursors of the ion-exchange membranes. The sulfonating of the porous polytetrafluoroethylene–polystyrene composites forms the membranes with ion-exchange capacity up to 2.8 mmol/g. The composition and ground physicochemical properties of the new proton-conducting composite membranes are investigated. The developed membranes were shown to have good transport properties. The proton conductivity of water-saturated membranes is as high as 0.13 S/cm at room temperature; the hydration number is 30. Comparative tests of the synthesized membranes and the commercial Nafion-115 membrane in a direct methanol fuel cell at 60°C showed the characteristics of the fuel cell with the developed membranes being at least not inferior to those of a Nafion-115-based cell. [ABSTRACT FROM AUTHOR]

Electrodiffusion of ions in both cation (CEM) and anion exchange membranes (AEM) has been studied with theoretical calculations and experimental studies. Calculations are based on the Finite Element Method (FEM) using COMSOL Multiphysics® software. Nernst-Planck equations are solved in multi-ionic systems where no closed form solutions are available. Simulations are compared with laboratory-scale experiments in terms of current efficiency and membrane selectivity. Simulations revealed unexpected features in transport, due to coupling of ionic fluxes when the local electroneutrality condition is assumed. Transport of weak electrolytes showed the importance of involving ionic equilibria along the concentration profiles in both solutions and membranes, compelling to consider ionic constituents. The advantage of the COMSOL simulations is the ease to find concentration and potential profiles across the entire system, and to split fluxes to diffusion and migration contributions, showing their coupling even in the absence of electric current.

This study investigates the influence of co-existing ions on the salinity gradient power generation performance of the reverse electrodialysis (RED) using three different commercial ion exchange membrane pairs. The feed solutions, including the mixture of two different salts, were prepared with 90 wt.% of NaCl and 10 wt.% of LiCl, KCl, CaCl2, MgCl2 or Na2SO4 by keeping the salt ratio between high concentrate solution and low concentrate solution constant as 1:30 (g/g) at various flow velocities (50, 125 and 200 mL/min). It was observed that the divalent ions exhibited a negative impact on the performance of the RED system due to their high valence and low ionic mobility depending on their high hydrated radius and low diffusion coefficients compared to those of the monovalent ions. On the other hand, the effect of the monovalent ions differed according to the properties of ion exchange membranes used in the RED stack. When the power generation performances of ion exchange membrane pairs employed in the RED stack were compared, it was considered that Neosepta AMX and CMX membranes provided the highest power density due to their low membrane thicknesses, low electrical resistances, and relatively high ion exchange capacities compared to other two commercial ion exchange membrane pairs.

Undesired water crossover through ion‐exchange membranes is a significant limitation in electrically driven desalination processes. The effect of mitigating water crossover is twofold: 1) The desalination degree is less reduced due to the unwanted removal of water, and 2) the brine concentration is increased due to decreased dilution by an unwanted crossover of water molecules. Hence, water crossover limits the desalination and concentration efficiency of the processes, while the energy demand to achieve a certain level of desalination or concentration increases. This effect is especially pronounced when treating high salinity solutions, which goes hand in hand with the crossover of many ions through the ion‐exchange membranes. A crosslinked coating for cation‐exchange membranes (CEMs) is presented in this work, which can significantly mitigate such undesired water crossover. The efficacy is demonstrated using the flow‐electrode capacitive deionization process applied for desalination and concentration of saline brines at feed concentrations of 60 and 120 g L−1 NaCl. With just a single coated CEM, the water crossover was reduced by up to 54%. [ABSTRACT FROM AUTHOR]

The wastewaters of galvanizing plants contain toxic heavy metals, which causes pollution of the environment and endangers it. The aim of the present study includes concentration of chromium (VI) ions from chromium plating wastewaters, purification of wastewater and its reuse for development of waste-free technological cycle. This study was carried out with the pilot electrodialysis apparatus designed by the authors and produced in the Institute engineering workshop using real plating rinse water of the plating shop. The authors obtained desalinated water which may be recirculated in rinsing bath and chromium salts concentrate that can be applied in chromium plating bath after correction. As a result of the conducted experiment, the ion-exchange membranes resistant to "poisoning" with chromium (VI) ions and stable in the process of regeneration were selected and the technological modes for stable operation of apparatus matched. [ABSTRACT FROM AUTHOR]

New effective ion-exchange membranes are needed for a variety of applications, with a particularly pressing need for membranes used in fuel cells and membrane water electrolysis. PVDF-based membranes are promising for these and other applications. Two samples of such membranes with a low water content are studied. The interest in the behavior of these samples is that with an increase in the bathing NaCl solution concentration, the diffusion permeability decreases, whereas usually it increases along with increasing membrane conductivity. The hypothesis is that with increasing concentration, the water content decreases even more, which leads to a narrowing of the intercluster ion-conducting channels and a reduction in the effective mobility of coions, since the latter have to go around narrowed sections of channels. To simulate the concentration dependence of conductivity, diffusion permeability and transport numbers for the two above samples, the microheterogeneous model is extended to describe the loss of water with increasing external concentration and take into account the decrease of coion percolation through the membrane. The results of simulation are compared with the experimental data. [Display omitted] • Concentration-dependent transport properties of PVDF-based membranes are studied. • Percolation is introduced in mechanistic-thermodynamic-microheterogeneous model. • Membrane microheterogeneous structure is taken into account. • Effect of low-water content on membrane structure is described. • Dependence of coion diffusion coefficients on water content and swelling degree is simulated. [ABSTRACT FROM AUTHOR]

Emerging technologies in nanotechnology and biomedical engineering have led to an increase in the use of implantable biomedical devices. These devices are currently battery powered which often means they must be surgically replaced during a patient’s lifetime. Therefore, there is an important need for a power source that could provide continuous, stable power over a prolonged time. Reverse electrodialysis (RED) based biopower cells have been previously used to generate continuous power from physiologically relevant fluids; however, the low salinity gradient that exists within the body limited the performance of the biopower cell. In this study, a miniaturized RED biopower cell design coupled with a salt cartridge was evaluated for boosting the salt concentration gradient supplied to RED in situ. For the salt cartridge, polysulfone (PSf) hollow fibers were prepared in-house and saturated with NaCl solutions to deliver salt and thereby enhance the concentration gradient. The effect of operational parameters including solution flow rate and cartridge salt concentration on salt transport performance was evaluated. The results demonstrated that the use of the salt cartridge was able to increase the salt concentration of the RED inlet stream by 74% which in turn generated a 3-fold increase in the open circuit voltage (OCV) of the biopower cell. This innovative adaptation of the membrane-based approach into portable power generation could help open new pathways in various biomedical applications.

In this study, the characteristic frequencies of the electrochemical impedance of ion-exchange membrane systems constituted by the membrane and two diffusion boundary layers adjacent to the membrane were investigated. Approximations of the impedance of the Randles equivalent electric circuit in multiple frequency ranges were considered, and the characteristic frequencies of the zeros and poles of orders ½ and 1 were derived. The characteristic geometric frequencies, those associated with the interfacial charge transfer and the diffusive transport processes, as well as those associated with the transitions between processes, were identified by means of analytical expressions.

The reverse electrodialysis heat engine (REDHE) is a promising salinity gradient energy technology, capable of producing hydrogen with an input of waste heat at temperatures below 100 °C. A salinity gradient drives water electrolysis in the reverse electrodialysis (RED) cell, and spent solutions are regenerated using waste heat in a precipitation or evaporation unit. This work presents a non-equilibrium thermodynamics model for the RED cell, and the hydrogen production is investigated for KCl/water solutions. The results show that the evaporation concept requires 40 times less waste heat and produces three times more hydrogen than the precipitation concept. With commercial evaporation technology, a system efficiency of 2% is obtained, with a hydrogen production rate of 0.38 gH2 m−2h−1 and a waste heat requirement of 1.7 kWh gH2−1. The water transference coefficient and the salt diffusion coefficient are identified as membrane properties with a large negative impact on hydrogen production and system efficiency. Each unit of the water transference coefficient in the range tw=[0–10] causes a −7 mV decrease in unit cell electric potential, and a −0.3% decrease in system efficiency. Increasing the membrane salt diffusion coefficient from 10−12 to 10−11 leads to the system efficiency decreasing from 2% to 0.6%.

In this work, a comparative study was carried out of the transport properties and performance in a hydrogen-air fuel cell of the membranes based on polymethylpentene (PMP) with grafted sulfonated polystyrene and the standard Nafion® 212 membrane. Grafted cation-exchange membranes (GCM) were obtained by radiation graft post-polymerization of styrene onto UV-exposed PMP film followed by sulfonation with chlorosulfonic acid. The proton-conductivity of the GCM membrane with an ion-exchange capacity of 2.9 ± 0.1 meq/g reaches 21 ± 1 mS cm−1 at room temperature and 95% relative humidity, which is twice higher the conductivity of the Nafion® under the same conditions. The GCM-1 H 2 -permeability of 2.06∙10−7 cm2 s−1 even slightly lower than that of the Nafion® 212 (2.14∙10−7 cm2 s−1). A comparison of these membranes in the membrane electrode assemblies (MEA) of hydrogen-air fuel cells (FC) shows that the use of the grafted membranes with the high ion-exchange capacity is highly promising. The maximum performance of FC with grafted and Nafion® 212 membrane are both close to 180 mW/cm2 at the current density of 400 mA/cm2. At the same time, the high degree of crosslinking of sulfonated polystyrene leads to a decrease in conductivity and does not give an advantage in gas permeability. • UV-radiation-induced post-grafting method was used to synthesize grafted PEM. • Membranes with 1.9 and 2.9 mg-eqv-SO 3 H/g and different cross-linking were investigated. • The performance of hydrogen-air fuel cell with new grafted membranes was investigated. • Maximal power of 180 mW/cm2 was achieved for grafted and Nafion®212 membrane. [ABSTRACT FROM AUTHOR]

As water scarcity has become a serious global issue, seawater reverse osmosis (SWRO) is considered as a promising technique to expand traditional water supplies. However, the reject brine from SWRO systems is still a major environmental concern. In this research, the monovalent selective electrodialysis (S-ED) was used to separate and recover one of the primary components, i.e., sodium chloride, from the SWRO brine, thereby avoiding the direct discharge of the brine and achieving the brine valorization. The permselectivity of selective ion-exchange membranes (IEMs) was elucidated by comparing with the standard IEMs in structure-property via membrane characterization techniques. Results indicated that the permselectivity of Selemion CSO membrane was attributed to the positive-charged layer with a low sulfonate/ammonium ratio of 1.28. Whereas the permselectivity of Selemion ASV membrane resulted from the highly cross-linked layer, according to the similar content of the fixed quaternary amines and the shift of the C‑N absorption peak. In addition, the effects of the current density and temperature on the membrane performance were studied, including permselectivity ( P Mg 2 + Na + and P SO 4 2 − Cl − ), Na+ recovery, and specific energy consumption (ESEC). Finally, the NaCl-rich brine with the total dissolved solid (TDS) value of 167.5 ± 3.3 g/L was obtained using SWRO brine with the initial TDS of 76.8 g/L. The Na+/Mg2+ mass ratio of the concentrate was 222.4, compared with the initial value of 9.7 in SWRO brine. [ABSTRACT FROM AUTHOR]

This data paper aims to provide data on the effect of the process settings on the fouling of an electrodialysis pilot installation treating a sodium chloride solution (0.1 M and 0.2 M) in the presence of humic acid (1 g/L). This data was used by “Colloidal fouling in electrodialysis: a neural differential equations model” [1] to construct a predictive model and provides interpretive insights into this dataset. 22 electrodialysis fouling experiments were performed where the electrical resistance over the electrodialysis stack was monitored while varying the crossflow velocity (2.0 cm/s - 3.5 cm/s) in the compartments, the current applied (1.41 A - 1.91 A) to the stack and the salt concentration in the incoming stream. The active cycle was maintained for a maximum of 1.5 h after which the polarity was reversed to remove the fouling layer. Additional data is gathered such as the temperature, pH, flow rate, conductivity, pressure in the different compartments of the electrodialysis stack. The data is processed to remove the effect of temperature fluctuations and some filtering is performed. To maximise the reuse potential of this dataset, both raw and processed data are provided along with a detailed description of the pilot installation and sensor locations. The data generated can be useful for researchers and industry working on electrodialysis fouling and the modelling thereof. The availability of conductivity and pH in all compartments is useful to investigate secondary effects of humic acid fouling such as the eventual decrease in membrane permselectivity or water splitting effects introduced by the fouling layer.

Ion-exchange membranes (IEMs) are a core component that greatly affects the performance of electrochemical energy conversion processes such as reverse electrodialysis (RED) and all-vanadium redox flow battery (VRFB). The IEMs used in electrochemical energy conversion processes require low mass transfer resistance, high permselectivity, excellent durability, and also need to be inexpensive to manufacture. Therefore, in this study, thin-reinforced anion-exchange membranes with excellent physical and chemical stabilities were developed by filling a polyethylene porous substrate with functional monomers, and through in situ polymerization and post-treatments. In particular, the thin-reinforced membranes were made to have a high ion-exchange capacity and a limited degree of swelling at the same time through a double cross-linking reaction. The prepared membranes were shown to possess both strong tensile strength (>120 MPa) and low electrical resistance (2). As a result of applying them to RED and VRFB, the performances were shown to be superior to those of the commercial membrane (AMX, Astom Corp., Japan) in the optimal composition. In addition, the prepared membranes were found to have high oxidation stability, enough for practical applications.

The study of the electrical conductivity of ion-exchange membranes in equilibrium electrolyte solutions is of great importance for the theory of membrane processes, in particular for practical electrodialysis. The purpose of the work is to determine the electrical conductivity of industrial ion-exchange membranes MK-40 and MA-40, as well as their basis—granules of a bulk layer of industrial ion exchangers KU-2-8 and EDE-10p, by differential and modified contact methods in electrolyte solutions and the development of a new methodology that will give the values that are closest to the true ones; determination of the dependence of electrical membrane conductivity depending on the type of counterion and concentration equilibrium solution and granules of a bulk layer of ion exchangers on the volume fraction of a dry ion exchanger with different degrees of compaction. It is shown that the dependence of the electrical conductivity of diaphragms on the electrolyte concentration, according to theoretical ideas, disappears under compression. It has been experimentally established that the difference method gives lower values of electrical conductivity in the region of low concentrations. The data obtained by the contact method are in good agreement with the results obtained for compressed diaphragms. The membrane conductivity decreases with increasing ion size.