Commercial Ion Exchange Membranes Research Articles

The Effect of Membrane and Catalyst for Cell Polarization of PEM Water Electrolysis

Commercial proton ion exchange membranes (Nafion 117, Dufont, USA) are generally supplied in the form of Na+ to storage. Pretreatment accelerate the ionic conductivity of membrane by converting the surface of the membrane into the functional group (-SO3H) having the form of proton ion. The pretreatment process may cause a significant increase in the total cost of water electrolysis and sometimes the expected results, i.e. reduction of membrane fouling, may not be achieved. In this study, we investigated the electrochemical characteristics of MEA according to the treatment condition of membrane and the type of catalyst such as Iridium black and Iridium oxide. Electrochemical and surface morphology of MEA were studied by I-V curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM).

Porous star-star polyelectrolyte multilayers for protein binding

This work employs layer-by-layer adsorption of star-poly[2-(dimethylamino)ethyl methacrylate] (star-PDMAEMA) and star-poly(acrylic acid) (star-PAA) to create porous coatings that bind the equivalent of many monolayers of lysozyme. AFM images of (star-PDMAEMA/star-PAA)n films on gold-coated wafers reveal pore diameters ranging from 100–550 nm, depending on the number of arms in the polymer and the number of bilayers, n, in the films. (Star-PDMAEMA/star-PAA)n coatings on Au-coated wafers bind the equivalent of up to 150 nm of lysozyme, and binding is greater for films containing star-PAA with 3, rather than 4, arms. Deposition of star-PAA/star-PDMAEMA films in porous hydroxylated nylon gives membranes that bind proteins via ion-exchange interactions. Such membranes capture as much as 120 mg of lysozyme per cm3 of membrane (equilibrium binding capacity), which is more than twice the capacity of commercial ion-exchange membranes, but films are unstable at neutral and high pH.

Application of the commercial ion exchange membranes in the all-vanadium redox flow battery

Three commercial anion exchange membranes and two commercial cation exchange membranes were tested to use as a separator in the all-vanadium redox flow battery (VRFB). Membrane properties such as an ionic conductivity and a permeability of each vanadium ion were evaluated. Ionic conductivities decreased in the order: Nafion117≈APS>NEPEM115>FAP-PP-475>FAP-PE-420. An anion exchange membrane had a low permeability of each vanadium ion compared to a cation exchange membrane. Energy efficiencies of VRFB using the commercial ion exchanges membrane had almost the same value in the range of 76.0–78.7%.

Salt concentration dependence of ionic conductivity in ion exchange membranes

Electric field driven ion transport in ion exchange membranes, often quantified by membrane resistance or ionic conductivity, is important for membrane-based technologies such as electrodialysis, batteries, fuel cells, etc. Various methods for measuring membrane ionic conductivity have been reported in the literature, but no widely accepted, standard protocol exists. Consequently, conflicting ionic conductivity results for widely studied commercial ion exchange membranes have been reported, leading to confusion regarding, for example, the salt concentration dependence of membrane ionic conductivity, especially for membranes equilibrated with dilute aqueous salt solutions. In this study, we report a simple, fast, reliable technique for measuring ionic conductivity based on direct contact between the membrane and electrodes. The technique was used to measure ionic conductivity values for a series of commercial ion exchange membranes as a function of external solution NaCl concentration (ranging from 0.001 to 5M). The salt concentration dependence of membrane ionic conductivity was rationalized within the Nernst-Einstein framework. At low external solution salt concentrations (< 0.3M), ionic conductivity values were essentially constant since mobile ion concentrations in the membranes approached a constant value (i.e., the fixed charge group concentration). At high salt concentrations (> 0.3M), ionic conductivity values increased with increasing salt concentration for three of the membranes, presumably due to increased ion sorption owing to weaker Donnan exclusion, and decreased for one membrane, presumably due to decreased ion diffusion coefficients resulting from osmotic deswelling.

Electrochemical impedance spectroscopy of enhanced layered nanocomposite ion exchange membranes

This work presents the enhancement of Cl−/SO42− mono-selectivity of layered nanocomposite anion exchange membranes (AEMs) and the mechanism that supports this improvement. These nanocomposite membranes are based on commercial polyethylene AEMs and a nanocomposite negative thin layer composed of sulfonated poly (2,6-dimethyl-1,4-phenylene oxide) and a functionalized nanomaterial, Fe2O3−SO42− nanoparticles or oxidized multi-walled carbon nanotubes CNTs-COO−. The mechanism for monovalent selectivity was confirmed by characterizing nanocomposite membranes and commercial heterogeneous ion exchange membranes (IEMs) using ζ-potential and electrochemical impedance spectroscopy (EIS). ζ-potential measurements confirmed the modification of the charge of surface of the membrane after being coated with the nanocomposite layer. EIS measurements showed a totally different electrical performance between layered nanocomposite membranes and commercial IEMs. The electrical data from EIS was fitted to a Maxwell-Wagner model providing an equivalent electric circuit (EEC) for each membrane. The observed differences in ECC were related to the structural differences of the membranes. A physical explanation of the phenomena that caused these differences is provided. The influence of ion concentration on EIS measurements was also studied. To the best of our knowledge, this is the first time that an ECC related to the structure of advanced layered IEMs is proposed.

Preparation of polyethylene membranes filled with crosslinked sulfonated polystyrene for cation exchange and transport in membrane capacitive deionization process

Commercial ion-exchange membranes are usually thick, and have high electrical resistances that can reduce the adsorption capacity of electrodes in membrane capacitive deionization (MCDI) cells. In this study, porous polyethylene (PE) membranes, filled with a sulfonated monomer, crosslinking agent (5, 10, 15wt%), and radical initiator, were subjected to polymerization and subsequent ion-exchange, to yield PE filled with crosslinked sulfonated polystyrene (PE-CSPS-5, 10, 15). PE-CSPS membranes were very thin (27μm), and exhibited moderate water uptake (26–35wt%) and ion-exchange capacity (0.70–1.0meq/g), and low electrical resistances (0.33–0.62Ω·cm2) compared with commercial ones. MCDI cells were assembled with either a PE-CSPS-5 membrane or a commercial cation-exchange membrane (CMX, IEC 1.5–1.8meq/g), and their performances studied using a 500ppm solution of NaCl. The current efficiency of the PE-CSPS-5-based MCDI cell showed slightly higher than that of the commercial CMX-based MCDI cell, which was attributed to the considerably lower electrical resistance of the membrane (0.33 vs. 2.9Ω·cm2), even though its IEC value is smaller (1.0 vs. 1.5–1.8meq/g). Our study reveals that supporting membranes filled with ion-exchange polymers have advantages over casting membranes in preparing membranes for MCDI application, with respect to dimentional stability and thickness.

Accounting for frame of reference and thermodynamic non-idealities when calculating salt diffusion coefficients in ion exchange membranes

Accurate evaluation of salt diffusion coefficients from transport rate data in ion exchange membranes requires accounting for frame of reference and non-ideal thermodynamic effects. Due to a lack of models and experimental data quantifying membrane ion activity coefficients, it has been impossible to evaluate the impact of non-ideal thermodynamic effects on observed salt diffusion coefficients. Here, a framework is presented that includes both frame of reference (i.e., convection) and non-ideal thermodynamic effects in calculating salt diffusion coefficients in ion exchange membranes. Effective concentration averaged NaCl diffusion coefficients were determined as a function of upstream NaCl concentration in commercial ion exchange membranes from NaCl permeability and sorption measurements via the solution-diffusion model. Frame of reference effects were evaluated using a version of Fick's law that accounts for convection. The factors necessary to account for non-ideal thermodynamic effects were developed using Manning's counter-ion condensation theory. At low upstream NaCl concentrations, frame of reference and non-ideal thermodynamic effects on diffusion coefficients were negligible. However, at higher upstream NaCl concentrations (e.g., >0.1M), both effects contribute measurably to NaCl diffusion coefficients. Correcting for frame of reference effects increased apparent NaCl diffusion coefficients. However, correcting for thermodynamic non-idealities of the ions sorbed into the membranes reduced apparent NaCl diffusion coefficients. Fortuitously, for the materials considered in this study, frame of reference and non-ideal thermodynamic effects nearly cancel each other.

Insights into Free Volume Variations across Ion-Exchange Membranes upon Mixed Solvents Uptake by Small and Ultrasmall Angle Neutron Scattering.

Ion-exchange membranes are composite separation materials increasingly used in a variety of electro-membranes and electrochemical processes. Although promising for solvent reclamation, to date, their main applications are limited to aqueous environments due to physicochemical and microstructural changes of the materials upon exposure to nonaqueous and mixed solvents solutions, affecting long-term stability and separation performance. In the present work, the structural changes of commercial and novel hybrid ion-exchange membranes in mixed methanol/water and ethanol/water solutions are assessed for the first time using ultra- and small-angle neutron scattering techniques. The interface between the ion-exchange functional layer and the mechanical support of the membranes is evaluated in the ultralow-q region, while a broad solvent-dependent peak at the mid-q region was correlated to the microstructural properties which are related to the free volume across the ion-exchange domains and to the materials electrical and nanoscale mechanical properties. The results of this study may offer new opportunities toward the development of an efficient separation process using ion-exchange membranes for the purification of fermentation broths toward biofuel generation.

Sharp rise in resistance of ion exchange membranes in low concentration NaCl solution

Abstract Using a modified impedance measurement technique, ohmic resistance of commercial ion exchange membranes (Selemion CMV and AMV as well as Neosepta CMX and AMX) was measured in low concentration aqueous NaCl solutions. The ohmic resistance increased by an order of magnitude as the NaCl concentration was reduced from 0.5 M to 0.017 M Resistance of cation exchange membranes increased more than the anion exchange membranes. Resistance increased monotonically with a decrease in the NaCl concentration and the variation of resistance could be explained very well using a model based on the Kohlrausch law of conductivity. The model also provided value of the tortuosity for the membranes. Tortuosity of the membranes was between 3.4 and 4.5.

Predicting Salt Permeability Coefficients in Highly Swollen, Highly Charged Ion Exchange Membranes.

This study presents a framework for predicting salt permeability coefficients in ion exchange membranes in contact with an aqueous salt solution. The model, based on the solution-diffusion mechanism, was tested using experimental salt permeability data for a series of commercial ion exchange membranes. Equilibrium salt partition coefficients were calculated using a thermodynamic framework (i.e., Donnan theory), incorporating Manning's counterion condensation theory to calculate ion activity coefficients in the membrane phase and the Pitzer model to calculate ion activity coefficients in the solution phase. The model predicted NaCl partition coefficients in a cation exchange membrane and two anion exchange membranes, as well as MgCl2 partition coefficients in a cation exchange membrane, remarkably well at higher external salt concentrations (>0.1 M) and reasonably well at lower external salt concentrations (<0.1 M) with no adjustable parameters. Membrane ion diffusion coefficients were calculated using a combination of the Mackie and Meares model, which assumes ion diffusion in water-swollen polymers is affected by a tortuosity factor, and a model developed by Manning to account for electrostatic effects. Agreement between experimental and predicted salt diffusion coefficients was good with no adjustable parameters. Calculated salt partition and diffusion coefficients were combined within the framework of the solution-diffusion model to predict salt permeability coefficients. Agreement between model and experimental data was remarkably good. Additionally, a simplified version of the model was used to elucidate connections between membrane structure (e.g., fixed charge group concentration) and salt transport properties.

Membrane Permeability Rates of Vanadium Ions and Their Effects on Temperature Variation in Vanadium Redox Batteries

The inevitable diffusion of vanadium ions across the membrane can cause considerable capacity loss and temperature increase in vanadium redox flow batteries (VRFBs) over long term operation. Reliable experimental data of the permeability rates of vanadium ions are needed for membrane selection and for use in mathematical models to predict long-term behavior. In this paper a number of ion exchange membranes were selected for detailed evaluation using a modified approach to obtain more accurate permeation rates of V2+, V3+, VO2+ and VO2+ ions. Three commercial ion exchange membranes—FAP450, VB2 and F930—are investigated. The obtained diffusion coefficients are then employed in dynamic models to predict the thermal behavior under specific operating conditions. The simulation results prove that smaller and more balanced permeability rates of V2+ and VO2+ ions are more important to avoid large temperature increases in the cell stack during stand-by periods at high states-of-charge with pumps off.

Osmotic Power Generation with Positively and Negatively Charged 2D Nanofluidic Membrane Pairs

In nature, hierarchically assembled nanoscale ionic conductors, such as ion channels and ion pumps, become the structural and functional basis of bioelectric phenomena. Recently, ion‐channel‐mimetic nanofluidic systems have been built into reconstructed 2D nanomaterials for energy conversion and storage as effective as the electrogenic cells. Here, a 2D‐material‐based nanofluidic reverse electrodialysis system, containing cascading lamellar nanochannels in oppositely charged graphene oxide membrane (GOM) pairs, is reported for efficient osmotic energy conversion. Through preassembly modification, the surface charge polarity of the 2D nanochannels can be efficiently tuned from negative (−123 mC m−2) to positive (+147 mC m−2), yielding strongly cation‐ or anion‐selective GOMs. The complementary two‐way ion diffusion leads to an efficient charge separation process, creating superposed electrochemical potential difference and ionic flux. An output power density of 0.77 W m−2 is achieved by controlled mixing concentrated (0.5 m) and diluted ionic solutions (0.01 m), which is about 54% higher than using commercial ion exchange membranes. Tandem alternating GOM pairs produce high voltage up to 2.7 V to power electronic devices. Besides simple salt solutions, various complex electrolyte solutions can be used as energy sources. These findings provide insights to construct cascading nanofluidic circuits for energy, environmental, and healthcare applications.

Permeability of Small Alcohols through Commercial Ion-Exchange Membranes Used in Electrodialysis

The use of solvent mixtures composed of water and organic cosolvents enables electrodialysis to remove poor water-soluble organic compounds from solutions. The flux of organic cosolvents forms the main problem for these applications because of changing cosolvent concentrations. The present paper investigates the permeability of small linear alcohols, namely, methanol, ethanol, and 1-propanol, through commercial ion-exchange membranes. The membrane permeability decreases with increasing molecular size of the cosolvent. This indicates that the transport is limited by steric hindrance in the membrane. However, the use of 1-propanol leads to a high pressure drop and a high permeability in certain membranes. In addition, the effect of operating parameters on the cosolvent permeability was tested. A change in current density has only a minor influence on the cosolvent flux. The flux of organic cosolvents was found to be mainly determined by the concentration gradient of alcohol across the membrane. The cosolven...

A 1.8 V Aqueous Supercapacitor with a Bipolar Assembly of Ion-Exchange Membranes as the Separator

We introduce a novel bipolar assembly of ion-exchange membranes as the separator for aqueous supercapacitors. The new bipolar separator enables the positive electrode and the negative electrode to operate in acidic electrolyte and alkaline electrolyte, separately. The bipolar separator increases the theoretically stable voltage window from 1.23 to 1.76 V for the device when pH 1 and pH 10 are selected for the positive and negative electrode, respectively, based on the pH tolerance of commercial ion exchange membranes. By considering the results from comprehensive electrolyte stability investigation, we charge the cells to 1.8 V, which increases the maximum cell discharge voltage to 1.77 V. A specific energy of 12.7 Wh/kg is achieved based on the electrodes’ mass, which is twice the value of the comparative best performing single electrolyte. The new cell configuration with the three-compartment bipolar separator effectively prevents the acid/base electrolyte cross diffusion, where after 10,000 cycles, the capacitance retention is 97% with coulombic efficiency maintained above 99.6% all through cycling. The design here may open up a new avenue toward high-energy aqueous energy storage devices.

Ionic polymer–metal composite actuators obtained from sulfonated poly(ether ether sulfone) ion-exchange membranes

The cost-effective and high-performance ionic polymer–metal composites (IPMC) were designed and prepared from ion-exchange membranes based on sulfonated poly(ether ether sulfone) (SPEES) with different degrees of sulfonation (DS). The precursor of SPEES, namely PEES, is commercially available and industrial grade. Moreover, the PEES can be transformed easily into ion-conductive SPEES through a simple sulfonation reaction. The ion exchange capacity (IEC) and water uptake (WU) of SPEES membranes increase with increasing their DS, and the proton conductivities of these hydrated SPEES membranes are subsequently enhanced. Compared with the commercial Nafion ion-exchange membrane, the SPEES membranes have higher IEC and WU. The IPMC actuators made of the SPEES membranes show the large bending strain and fast response under electric stimulation. The SPEES membrane with the highest DS (SPEES4) shows the best performance of IPMC actuators. The electromechanical behaviors of these IPMC actuators indicate that the SPEES is a candidate to substitute Nafion.

Thermal potential of ion-exchange membranes and its application to thermoelectric power generation

The low efficiency and high price of thermoelectric semiconductors has generated interest in unconventional forms of thermoelectric materials. In this article, ionic thermoelectricity has been studied with commercial ion-exchange membranes for different aqueous 1:1 electrolytes. The theory of thermal membrane potential has been derived taking into account the ionic heats of transport, the non-isothermal Donnan potentials, the temperature polarization, and the thermally-induced concentration polarization of the electrolyte. Also the generated thermoelectric power has been experimentally studied. The experiments show good agreement with the theory, and suggest ways for systematic improvement of the system performance.

Bipolar membrane electrodialysis for treatment of sodium acetate waste residue

Abstract Large amounts of solid waste residue containing high salinity and a series of organic impurities are produced during the manufacturing process of dithianon in insecticide factories, posing a severe environmental pollution problem. Here sodium acetate (CH 3 COONa) waste residue is firstly tested by diffusion dialysis (DD) to investigate the permeability of different commercial ion exchange membranes. Selemion CMV and AMV membranes show low permeability to the organic impurities of the waste residue, and hence are chosen for the following bipolar membrane electrodialysis (BMED) experiments to regenerate acid and base. The BMED firstly uses a BP-A-C-BP configuration to select an optimized current density of ∼50 mA/cm 2 . Afterwards, four membrane stack configurations are compared including BP-A-C-BP, C-BP-A-C, BP-C-BP and BP-A-BP. In consideration of the high current efficiency, low energy consumption, and high concentrations of the produced acid/base, C-BP-A-C is a favorable configuration. Finally, the addition of a strong acid 001 ∗ 7 type of cation-exchange resin into acid compartment can substantially decrease the voltage drop across the stack and reduce the energy consumption. The C-BP-A-C configuration at 50 mA/cm 2 can have a high output (0.491 mol/L CH 3 COOH and 0.556 mol/L NaOH), high current efficiency (87.7% for CH 3 COOH and 99.0% for NaOH), and a relatively low energy consumption (22.3 kW h/kg CH 3 COOH and 29.7 kW h/kg NaOH). Overall, this study illustrates the practical significance of BMED process for treating sodium acetate waste residue, including reducing soil and water pollution and producing valuable products in insecticide industries.

Electrodialysis aided desalination of crude glycerol in the production of biodiesel from oil feed stock

Electrodialysis (ED) is a proven membrane process used mainly in desalination of brackish/seawater, salt production and separation of ionizable compounds from aqueous industrial solutions. In the biodiesel industry, trans-esterification reaction produces the fuel along with a mixture of byproducts containing glycerol, methanol, water, soap and unreacted catalyst. Considering the massive scale of crude glycerol formed as a byproduct in the tremendously increasing number of biodiesel industries worldwide, there is a great demand for newer methods for purification of crude to pure glycerol. The present study focuses on the separation of sodium sulfate (Na2SO4) salt formed during neutralization of alkaline catalysts, from the crude glycerol. ED studies were conducted with commercial AMI-7001 and CMI-7000 ion exchange membranes. Limiting current densities (LCDs) were determined at different feed flow rates. The ED cost estimation studies were performed by optimizing a single process parameter, namely, linear velocity. The experimental results demonstrated that the membranes exhibited sufficient chemical and thermal stability and successfully separated more than 95% of Na2SO4 from crude glycerol. ED was observed to be a simple and cost effective technology, which provides a competitive value addition to biodiesel production through byproduct recovery.

Monoethanolamine Reclamation Using Electrodialysis

Monoethanolamine (MEA) is the benchmark solvent for the capture of carbon dioxide from both natural gas and flue gas streams. Despite its effectiveness in absorbing CO2, this solvent can react with impurities in the gas stream to form heat stable salts and other degradation products. These impurities can cause problems such as an increase in solvent viscosity and corrosion of the operating units. Thus, a number of approaches have been considered to mitigate the occurrence of these problems. In this paper, the use of electrodialysis as an online MEA reclamation process in a postcombustion CO2 capture facility is investigated. The study shows that high heat stable salts removal can be achieved with a high MEA recovery. However, it is necessary to limit the current density, particularly at lower salt concentrations, to reduce water splitting. The stability of the commercial ion-exchange membranes in the highly alkaline solvent is also investigated. The results show that the membranes are stable upon exposure to 30 wt % MEA for at least 4.5 months.

Specific ion effects on membrane potential and the permselectivity of ion exchange membranes.

Membrane potential and permselectivity are critical parameters for a variety of electrochemically-driven separation and energy technologies. An electric potential is developed when a membrane separates electrolyte solutions of different concentrations, and a permselective membrane allows specific species to be transported while restricting the passage of other species. Ion exchange membranes are commonly used in applications that require advanced ionic electrolytes and span technologies such as alkaline batteries to ammonium bicarbonate reverse electrodialysis, but membranes are often only characterized in sodium chloride solutions. Our goal in this work was to better understand membrane behaviour in aqueous ammonium bicarbonate, which is of interest for closed-loop energy generation processes. Here we characterized the permselectivity of four commercial ion exchange membranes in aqueous solutions of sodium chloride, ammonium chloride, sodium bicarbonate, and ammonium bicarbonate. This stepwise approach, using four different ions in aqueous solution, was used to better understand how these specific ions affect ion transport in ion exchange membranes. Characterization of cation and anion exchange membrane permselectivity, using these ions, is discussed from the perspective of the difference in the physical chemistry of the hydrated ions, along with an accompanying re-derivation and examination of the basic equations that describe membrane potential. In general, permselectivity was highest in sodium chloride and lowest in ammonium bicarbonate solutions, and the nature of both the counter- and co-ions appeared to influence measured permselectivity. The counter-ion type influences the binding affinity between counter-ions and polymer fixed charge groups, and higher binding affinity between fixed charge sites and counter-ions within the membrane decreases the effective membrane charge density. As a result permselectivity decreases. The charge density and polarizability of the co-ions also appeared to influence permselectivity leading to ion-specific effects; co-ions that are charge dense and have low polarizability tended to result in high membrane permselectivity.