Ion-exchange Membranes Research Articles

Transport Numbers and Electroosmosis in Cation-Exchange Membranes with Aqueous Electrolyte Solutions of HCl, LiCl, NaCl, KCl, MgCl2, CaCl2 and NH4Cl

Electroosmosis reduces the available energy from ion transport arising due to concentration gradients across ion-exchange membranes. This work builds on previous efforts to describe the electroosmosis, the permselectivity and the apparent transport number of a membrane, and we show new measurements of concentration cells with the Selemion CMVN cation-exchange membrane and single-salt solutions of HCl, LiCl, NaCl, MgCl2, CaCl2 and NH4Cl. Ionic transport numbers and electroosmotic water transport relative to the membrane are efficiently obtained from a relatively new permselectivity analysis method. We find that the membrane can be described as perfectly selective towards the migration of the cation, and that Cl− does not contribute to the net electric current. For the investigated salts, we obtained water transference coefficients, tw, of 1.1± 0.8 for HCl, 9.2 ± 0.8 for LiCl, 4.9 ± 0.2 for NaCl, 3.7 ± 0.4 for KCl, 8.5 ± 0.5 for MgCl2, 6.2 ± 0.6 for CaCl2 and 3.8 ± 0.5 for NH4Cl. However, as the test compartment concentrations of LiCl, MgCl2 and CaCl2 increased past 3.5, 1.3 and 1.4 mol kg−1, respectively, the water transference coefficients appeared to decrease. The presented methods are generally useful for characterising concentration polarisation phenomena in electrochemistry, and may aid in the design of more efficient electrochemical cells.

Ultramicroporous Tröger's Base Framework Membranes With Ionized Sub-nanochannels for Efficient Acid/Alkali Recovery.

Membrane technology holds significant potential for the recovery of acids and alkalis from industrial wastewater systems, with ion exchange membranes (IEMs) playing a crucial role in these applications. However, conventional IEMs are limited to separating only monovalent cations or anions, presenting a significant challenge in achieving concomitant H⁺/OH⁻ permselectivity for simultaneous acid and alkali recovery. To address this issue, the charged microporous polymer framework membranes are developed, featuring rigid Tröger's Base network chains constructed through a facile sol-gel process. The intrinsic ultramicropore confinement and quaternary ammonium-charged functional groups provide ultrahigh size-sieving capability and enhanced Donnan exclusion for H⁺/OH⁻ selectivity; meanwhile, the internal protoplasmic channels of the polymer frameworks serve as highways for rapid ion transfer. The resulting membrane achieves high H⁺/Fe2⁺ and OH⁻/WO₄2⁻ selectivities of 694.4 and 181.0, respectively, for concurrent acid and alkali separation in diffusion dialysis and electrodialysis processes over extended operational periods (exceeding 1600 and 600 h, respectively), while maintaining remarkable transport rates. These results outperform most literature-reported and nearly all commercially available membranes. This study validates the novel applicability of polymer framework materials with ionized angstrom-scale channels and versatile functionalities in high-performance IEMs for acid/alkali resource recovery.

ZIF-8-Embedded Cation-Exchange Membranes with Improved Monovalent Ion Selectivity for Capacitive Deionization

ZIF-8-Embedded Cation-Exchange Membranes with Improved Monovalent Ion Selectivity for Capacitive Deionization

A Zero-Gap Electrolyzer Enables Supporting Electrolyte-Free Seawater Splitting for Energy-Saving Hydrogen Production.

Membrane-assisted direct seawater splitting (DSS) technologies are actively studied as a promising route to produce green hydrogen (H2), whereas the indispensable use of supporting electrolytes that help to extract water and provide electrochemically-accelerated reaction media results in a severe energy penalty, consuming up to 12.5 % of energy input when using a typical KOH electrolyte. We bypass this issue by designing a zero-gap electrolyzer configuration based on the integration of cation exchange membrane and bipolar membrane assemblies, which protects stable DSS operation against the precipitates and corrosion in the absence of additional supporting electrolytes. The heterolytic water dissociation function of the bipolar membrane in situ creates an asymmetric acidic-alkaline environment, kinetically facilitating H2 and O2 evolution reactions. When working in natural seawater without any chemical inputs, this zero-gap electrolyzer sustains nearly 100 % Faradaic efficiency toward H2 for 120 h at a current density of 100 mA cm-2. With the high-integrity merit, our electrolyzer can be facilely scaled up into practical cell stacks with significantly increased active area and promising prospects for volume/space-sensitive application scenarios. This electrolyzer concept opens an underexplored design space for energy-saving H2 production from low-grade saline water sources, being complementary to, and potentially competitive with the pre-purification Schemes.

Miscible Polymer Blend Membranes Bearing Pyrrolidone for Fractioning Sulfuric Acid and Sulfates

ABSTRACTIon exchange membranes of new chemistry based on polymer blends are proposed through a convenient solution‐blending process using the hydrophobic commodity polymer polyvinyl chloride (PVC) and the hydrophilic polyvinylpyrrolidone (PVP), which are completely miscible. The pyrrolidone groups can be protonated to form oxonium ions, functioning as transient fixed positive charges for fractioning sulfuric acid and sulfates via diffusion. The influence of PVC molecular weight and the membrane composition on the physical, chemical properties, and mass transfer performance of PVC‐PVP blend membranes was systematically investigated. After equilibrium in 2.68 mol/L sulfuric acid, the sulfuric acid, and water contents in the blend membranes increase with the increase of the membrane PVP contents (20–75 wt%). The permeability coefficients of sulfuric acid and ferrous sulfate for the blend membranes also exhibit a gradual increase. Membranes of mass transfer properties comparable to commercial ones can be easily obtained by tuning the membrane PVP contents. It is proved that the larger sulfuric acid permeability over sulfates (FeSO4 as an example) is due to both larger solubility and diffusion coefficient of sulfuric acid in the membrane phase. The optimal PVC‐PVP blend membranes have shown nice performance in fractioning sulfuric acid from sulfates, when treating titania waste acid. This study provides valuable guidance for the design of high‐performance yet low‐cost ion exchange membranes with pyrrolidone chemistry from commodity polymers for resource recovery.

Nafion coated nanopore electrode for improving electrochemical aptamer-based biosensing.

The transition to a personalized point-of-care model in medicine will fundamentally change the way medicine is practiced, leading to better patient care. Electrochemical biosensors based on structure-switching aptamers can contribute to this medical revolution due to the feasibility and convenience of selecting aptamers for specific targets. Recent studies have reported that nanostructured electrodes can enhance the signals of aptamer-based biosensors. However, miniaturized systems and body fluid environments pose challenges such as signal-to-noise ratio reduction and biofouling. To address these issues, researchers have proposed various electrode coating materials, including zwitterionic materials, biocompatible polymers and hybrid membranes. Nafion, a commonly used ion exchange membrane, is known for its excellent permselectivity and anti-biofouling properties, making it a suitable choice for biosensor systems. However, the performance and mechanism of Nafion-coated aptamer-based biosensor systems have not been thoroughly studied. In this work, we present a Nafion-coated gold nanoporous electrode, which excludes Nafion from the nanoporous structures and allows the aptamers immobilized inside the nanopores to freely detect chosen targets. The nanopore electrode is formed by a sputtering and dealloying process, resulting in a pore size in tens of nanometers. The biosensor is optimized by adjusting the electrochemical measurement parameters, aptamer density, Nafion thickness and nanopore size. Furthermore, we propose an explanation for the unusual signaling behavior of the aptamers confined within the nanoporous structures. This work provides a generalizable platform to investigate membrane-coated aptamer-based biosensors.

Electrodialysis with Bipolar Membranes to valorise saline waste streams: Analysing the fate of valuable minor elements.

Brine mining can represent a valuable non-conventional resource for the extraction of Mg, Li, B, Sr and other Trace Elements (TEs) such as Rb, Cs, whose recoveries require chemical reagents such as alkaline and acidic solutions. In a circular strategy, these required chemicals can be produced in-situ through Electrodialysis with Bipolar Membranes (EDBM). In this work, a laboratory EDBM unit was operated using real brines from Trapani saltworks to investigate, for the first time, the migration of minor and trace ions, as Li, B, Sr, Cs and Rb through ion-exchange membranes (IEMs). Two different operating configurations were tested by feeding real brines: i) only in the salt channel or ii) in both salt and alkaline compartments. Trace ions migration was assessed by determining their apparent transport number in IEMs to better understanding their "fate" within the EDBM process. The use of real solutions in the base channel resulted in a 50% reduction in the process water demand, while achieving similar overall Current Efficiencies (75-78%) and Specific Energy Consumptions (1.50-1.80 kWh/kgNaOH) compared to the reference layout, where real brine was only fed in the salt compartment. Li, Rb, Sr and Cs were mostly transported across the cation-exchange membrane and concentrated in the alkaline channel. Such results lay the ground for the use of complex (multi-ionic) solutions and new designs of the EDBM process that can be operated in integrated chains to valorise saline wastes, reducing water consumption and avoiding the dilution of trace elements before their selective recovery.

Novel ionic liquid-infused PVA-based anion exchange membranes boosting bioelectricity yield from microbial fuel cells.

The goal of this research is to develop and characterize low-cost NH4I doped polyvinyl alcohol (PVA)-4-ethyl-4-methylmorpholiniumbromide (ionic liquid) anion exchange membranes (AEM) and its application for membrane cathode assembly. Physical characterization like FTIR, POM, and XRD notified the functional groups, basic structure, and amorphosity of the produced membrane, and it was employed in single-chambered microbial fuel cells (sMFCs) as a separator. The membranes in terms of oxygen diffusion, proton conductivity, and ion exchange capabilities were evaluated. PVA-ionic liquid composite membrane had a greater volumetric power density (PD) with a rise in the ionic liquid concentration, owing to lower internal resistance and reduced biofouling. Ionic conductivity also reduces as loading increases over a certain level of concentration. The incorporation of ionic liquid into the membrane had a considerable impact on impedance minimization (an enhancement in anionic conductivity) and biofouling. When MFC was used with a PVA-ionic liquid-based membrane cathode assembly (MCA), the highest PD of 7.98W/m3 was attained which is better than other composite membranes. The MCA surface area boosted the power output. The PVA-ionic liquid composite membrane proved to be a viable alternative to the more costly commercially available MFC membrane. This paper's novelty lies in synthesizing ammonium iodide (NH4I) doped PVA-ionic liquid membrane and further utilizing it as a separator in MFC. Also, this study demonstrates the membrane's potential for enhancing MFC performance, establishing it as a viable alternative to expensive commercial membranes.

Elucidating the thermo-mechano-chemical stability and electrochemical potential of PVP@ZP+Ze composite ion exchange membrane for industrial application

Elucidating the thermo-mechano-chemical stability and electrochemical potential of PVP@ZP+Ze composite ion exchange membrane for industrial application

Cascade charged channels in monovalent selective cation exchange membranes enable highly efficient separation

Cascade charged channels in monovalent selective cation exchange membranes enable highly efficient separation

Investigation of Influencing Factors on Power Generation Performance in Reverse Electrodialysis

The importance of meeting energy demands from renewable sources is growing daily. Reverse electrodialysis (RED) is a membrane-based technology that produces energy using electrolyte solutions with different salinities. This study has generated energy from the RED system using the commercial Fujifilm Type II ion exchange membranes (IEMs). Many parameters affect the power generation performance of the RED system. This study systematically investigated the parameters, the presence of divalent ions and organic molecules, the electrolyte solution concentration, and the flow velocity. The flow velocity results indicated that energy efficiency increased with increasing flow velocity of the electrolyte solutions. The presence of divalent ions created uphill transport. The results showed that increasing the mole ratio of divalent ions in the feed electrolyte solutions dramatically decreased the RED system performance due to increasing resistances. The organic fouling test of the anion exchange membranes (AEMs) was carried out using a real humic and fulvic acid mixture under static conditions. The results indicated that fouling layers formed in the AEMs structure, and these layers decreased by 30% of RED performance. Lastly, the RED system's long-term performance was tested for 4 hours at a constant current density of 8 A/m2 before and after AEM fouling experiments. The results revealed the fouling layers severely reduced the power generation performance of the RED system.

High-Performance and Anti-Freezing Moisture-Electric Generator Combining Ion-Exchange Membrane and Ionic Hydrogel.

Moisture-electric generators (MEGs), which convert moisture chemical potential energy into electrical power, are attracting increasing attention as clean energy harvesting and conversion technologies. However, existing devices suffer from inadequate moisture trapping, intermittent electric output, suboptimal performance at low relative humidity (RH), and limited ion separation efficiency. This study designs an ionic hydrogel MEG capable of continuously generating energy with enhanced selective ion transport and sustained ion-to-electron current conversion at low RH by integrating an ion-exchange membrane (IEM-MEG). A single IEM-MEG exhibits a maximum open-circuit voltage (VOC) of 0.815 V and a short-circuit current (ISC) of 101 µA at 80% RH. Even at a low RH of 10%, a stable VOC of 0.43 V and ISC of 11 µA can be generated. Moreover, the antifreeze performance of the device is improved by adding LiCl, which significantly expands its operational range in low-temperature environments. Finally, a simple series-parallel connection of six IEM-MEGs can yield an enhanced VOC of 4.8 V and a ISC of ≈0.6 mA, and the scalable units can directly power commercial electronics. This study provides new insights into the design of MEGs that will advance the development of green energy conversion technologies in the future.

Entropy Production in an Electro-Membrane Process at Underlimiting Currents—Influence of Temperature

The entropy production in the polarization phenomena occurring in the underlimiting regime, when an electric current circulates through a single cation-exchange membrane system, has been investigated in the 3–40 °C temperature range. From the analysis of the current–voltage curves and considering the electro-membrane system as a unidimensional heterogeneous system, the total entropy generation in the system has been estimated from the contribution of each part of the system. Classical polarization theory and the irreversible thermodynamics approach have been used to determine the total electric potential drop and the entropy generation, respectively, associated with the different transport mechanisms in each part of the system. The results show that part of the electric power input is dissipated as heat due to both electric migration and diffusion ion transports, while another part is converted into chemical energy stored in the saline concentration gradient. Considering the electro-membrane process as an energy conversion process, an efficiency has been defined as the ratio between stored power and electric power input. This efficiency increases as both applied electric current and temperature increase.

Analytical Solutions and Computer Modeling of a Boundary Value Problem for a Nonstationary System of Nernst–Planck–Poisson Equations in a Diffusion Layer

This article proposes various new approximate analytical solutions of the boundary value problem for the non-stationary system of Nernst–Planck–Poisson (NPP) equations in the diffusion layer of an ideally selective ion-exchange membrane at overlimiting current densities. As is known, the diffusion layer in the general case consists of a space charge region and a region of local electroneutrality. The proposed analytical solutions of the boundary value problems for the non-stationary system of Nernst–Planck–Poisson equations are based on the derivation of a new singularly perturbed nonlinear partial differential equation for the potential in the space charge region (SCR). This equation can be reduced to a singularly perturbed inhomogeneous Burgers equation, which, by the Hopf–Cole transformation, is reduced to an inhomogeneous singularly perturbed linear equation of parabolic type. Inside the extended SCR, there is a sufficiently accurate analytical approximation to the solution of the original boundary value problem. The electroneutrality region has a curvilinear boundary with the SCR, and with an unknown boundary condition on it. The article proposes a solution to this problem. The new analytical solution methods developed in the article can be used to study non-stationary boundary value problems of salt ion transfer in membrane systems. The new analytical solution methods developed in the article can be used to study non-stationary boundary value problems of salt ion transport in membrane systems.

Enhancement of IPMC Bending Controllability Through Immobile Negative Charges and Electrochemically Reactive Substances Within IPMC Body

A well-known soft actuator, called ionic polymer–metal composite (IPMC), is a type of electroactive polymer (EAP) that operates in bending mode. Despite its ability to exhibit large bending, its bending controllability is often poor. Therefore, identifying the key factor that allows IPMC to bend without losing its large bending capability is a natural inquiry for researchers studying IPMC for practical applications. Our study found that the sign of the immobile charge carried by the ion exchange membrane of IPMC governs its bending controllability. We also discovered that using a negatively charged ion exchange membrane, rather than a positively charged one, is highly preferable for IPMC applications. It was also found that using a doping process and an electrochemically active electrode is essential for inducing effective bending in IPMC.

Changes in Amorphous and Crystalline Phases of Ion-exchange Membranes MA-41P and MK-40 in the Separation of Industrial Solutions by Electrodeionization and Electrodialysis Methods

Changes in Amorphous and Crystalline Phases of Ion-exchange Membranes MA-41P and MK-40 in the Separation of Industrial Solutions by Electrodeionization and Electrodialysis Methods

Continuous packed bed column removal of Cr6+, Cd2+, and Pb2+ ions from synthetic wastewater using polymeric ultra‐permeable and biodegradable ferromagnetic nanocomposite membrane

AbstractWater purification techniques, including membrane technologies, ion exchange and adsorption, chemical/biochemical reduction, and electrochemical processes, have been developed to remove/recover metal ions species from polluted wastewater. This work assessed the efficiency of polymeric, biodegradable, ultra‐permeable and magnetic nanocomposite membrane (CNCs/N6@Fe3O4‐CT) in a continuous packed bed column for the removal of Cd(II), Cr(VI), and Pb(II) metal ions from synthetic wastewaters. The eco‐compatibility of CNCs/N6@Fe3O4‐CT was increased using chitosan biopolymer. Fe3O4 nanoparticles increased the surface area and improved the separation process. CNCs and N6 polymeric materials enhanced their strength, porosity, and additional binding sites. The CNCs/N6@Fe3O4‐CT nanocomposite membrane was employed as packing material in a fixed‐bed lab‐scale column (height 30 cm, diameter 1.5 cm) to constantly remove Cd(II), Cr(VI), and Pb(II) metal ions from synthetic wastewaters and actual hexavalent chromium tannery effluent. The studies were carried out with different initial metal ion concentrations (10, 20, and 30 mg/L), input flow rates (2, 4, and 6 mL/min), and solution pH values (2.0, 5.0, and 8.0). The obtained experimental data from the breakthrough curves was fitted to the traditional dynamic Thomas model, Yoon‐Nelson, and Bed Depth Service Time (BDST) model.

Effect of ion exchange resin membranes and activated carbon electrodes in water desalination using capacitive deionization technique with saline streams

Abstract Water contamination is increasing drastically today, and the government consistently works to reduce water pollution. This paper focuses on desalinating saline water using a capacitive deionization technique using activated carbon electrodes and ion exchange resin membranes. The developed model of the capacitive deionization cell works within 1.2 V, and the potential difference between the electrodes is varied within the threshold voltage of water. The concentrations of magnesium, sodium, and chlorine are measured in this investigation. The performance of the system was analyzed with a varied concentration of resin ion exchange membrane and various potential differences. The behavior of the capacitance deionization cell and rate with the conductance of water-electrolyte was studied. After the removal of ions, the conductivity of the electrolyte was reduced. Ion exchange resins are utilized to increase the electrical conductivity, which leads to an increase in the deionization rate. The ion exchange is carried out through the activated porous carbon electrodes. The experiment was carried out with varied voltages in saline streams, and the concentration of ions was evaluated. Due to the migration of positive and negative ions to the respective electrodes. The portable desalination model of efficient desalination level is derived. The energy and performance efficiencies are taken into consideration to evaluate the developed model. The cost of deionization is reduced compared with the reverse osmosis process. The deionization rate is high, leading to the production of a vast quantity of conditioned water for irrigation purposes. The study demonstrated that capacitive deionization (CDI) with activated carbon electrodes and ion exchange resin membranes effectively removes ions like magnesium, sodium, and chlorine, reducing water conductivity. Operating efficiently within a low-voltage range, the CDI system showed a high deionization rate suitable for large-scale applications, with lower costs than traditional reverse osmosis.

Interface Engineering by Molecular Layer Deposition on Polymer Membrane for Selective Ion Transport.

Molecular layer deposition (MLD) of ethylene glycol-alucone (EG-alucone) on the Nafion cation exchange membrane is investigated to understand its impact on the morphology of the composite and consequent enhancement of ion transport selectivity. X-ray photoelectron spectroscopy, scanning electron microscopy, Density functional theory, and Doppler broadening positron annihilation spectroscopy are comprehensively employed to examine the morphology of the composite, particularly the engineered interface between EG-alucone and Nafion. These studies reveal the diffusion and subsequent reaction of the Lewis-acidic trimethyl aluminum precursor with the polymer substrate during MLD. The Al─F bond, thus formed, modifies the well-defined microstructures of Nafion and creates a distinct hybrid region with size-based exclusion properties. Post-MLD hydration partially converts the deposited EG-alucone to alumina, reshaping the surface morphology and potentially forming a conformal top layer. The positively charged nature of this top layer, along with the steric sieving effect at the EG-alucone-polymer interface, contribute to the observed improvement in monovalent ion selectivity (Cs+/Na+ = 1.99 ±0.08 & Cs+/Ba2+ = 1.50 ±0.05) without significantly compromising membrane conductivity. A three-layer model of the composite membrane, supported by electrochemical impedance spectroscopy and radiotracer-based transport measurements, elucidates the structure-property relationship responsible for the observed selective ion transport.

Dispatch model of park-level integrated energy system with photovoltaic/thermal hydrogen generation equipment: A scenario analysis method based on improved K-means clustering

As the carbon emission problem brought by the traditional energy consumption pattern is becoming more and more prominent, it has become a common strategic choice for all countries to realize the carbon-neutral goal and to drive energy conversion to clean and renewable energy. Meanwhile, the significant uncertainty of renewable energy sources and their large-scale access to the grid poses new challenges to power system operation and dispatch. Therefore, this paper proposes a dispatch model for the park-level integrated energy system (PIES) with photovoltaic/thermal (PV/T) hydrogen generation equipments based on improved stepped carbon trading and adopts a scenario analysis method based on improved K-means clustering to cope with the uncertainties of the multi-energy loads and PV/T output. First, the PV/T model is constructed through five energy balance equations of the glass protection screen, solar panel, heat pipe, water inside the heat pipe, and heat storage tank, which is further combined with the hydrogen ion exchange membrane electrolyzer (HIEME) to analyze the energy flow conversion in the process of hydrogen production by the coupled equipment. Second, an improved stepped carbon trading price model is proposed by constructing a continuously monotonically increasing trading price function. Finally, based on the improved stepped carbon trading mechanism, the day-ahead dispatching model aims to optimize the sum of PIES operation cost and carbon trading cost, and the example simulation is carried out by the scenario analysis method based on improved K-means clustering. The simulation results show that the proposed model has certain significance in hydrogen production efficiency and carbon emission reduction.