Amphoteric Ion Exchange Membrane Research Articles

Amphoteric ion-exchange membranes with superior mono-/bi-valent anion separation performance for electrodialysis applications

Fabricating stable mono-/multi-valent anion-selective membranes with high perm-selectivity for electrodialysis (ED) applications is critical but challengeable. In this work, we have fabricated a series of novel homogeneous monovalent anion-selective amphoteric ion-exchange membranes (AIEMs, PAES-im-Xc) based on a long-side-chain type imidazolium-functionalized poly(arylene ether sulfone) cross-linked with 4,4′-diazostilbene-2,2′-disulfonic acid disodium salt (DAS) for ED. By tuning the mass percent of DAS added, low swelling ratio but appreciably high anion perm-selectivity (in Cl–/SO42– system) of optimized AIEM are achieved to values of 8.0% and 47.12 at current density of 2.5 mA cm–2, respectively. In particular, at an enhanced current density of 5.0 mA cm–2, its perm-selectivity reaches 12.5, significantly outperforming commercial monovalent anion-selective Neosepta ACS (5.27). The appreciably high perm-selectivity possibly arises from pore-size sieving effect from dense matrix structure with cross-linkings and strong electrostatic repulsion between negative fixed –SO3– groups and negative divalent ions of SO42– in feeding solution. The superior performances might be particularly interesting findings that can facilitate the development of advanced mono-/bi-valent anion-selective membranes in applications of sea water desalination, resource recovery and water treatment/pretreatment etc..

Semi-Interpenetrating Network-Type Cross-Linked Amphoteric Ion-Exchange Membrane Based on Styrene Sulfonate and Vinyl Benzyl Chloride for Vanadium Redox Flow Battery.

Clean energy is the main requirement for human life. Redox flow battery may be an alternative to fossil fuels. An ion-exchange membrane is the heart of the redox flow battery. In the present study, we synthesize semi-interpenetrating cross-linked copolymer amphoteric ion-exchange membranes (AIEMs) with a partially rigid backbone. The styrene sulfonate and vinyl benzyl chloride monomers are used as the cationic and anionic moieties into the AIEMs. Three different types of quaternizing agents are used to convert a primary amine into a quaternary amine group. Here, we avoid the use of the carcinogenic chemical CMME, commonly used for the synthesis of anion-exchange membranes. The prepared membranes exhibit good electrochemical and physicochemical properties with a high acidic stability. The membranes also show moderate water uptake and dimensional change. The ZWMO membrane shows better properties among the AIEMs, with an ionic conductivity of 3.12 × 10–2 S cm–1 and 5.49 water molecules per functional group. The anion and cation-exchange capacities of the ZWMO membranes are calculated to be 1.11 and 0.62 mequiv/g. All AIEMs show good thermal and mechanical stabilities, calculated by differential scanning calorimetry, dynamic mechanical analysis, and universal testing machine analysis. The membranes show low vanadium ion permeability than the commercial membrane Nafion for their use in vanadium redox flow batteries. Further, the AIEMs are applied in redox flow batteries as separators and deliver good results with the charging and discharging phenomena, with 87% voltage efficiency and 91% current efficiency.

A sandwiched bipolar membrane for all vanadium redox flow battery with high coulombic efficiency

Due to the good balance between the low vanadium permeability and high proton conductivity, AIEM (amphoteric ion exchange membrane) has attracted vast consideration for all vanadium redox flow battery (VRB) application. Similar to the AIEM, BPMs (bipolar membranes) also have both anion and cation exchange groups in the anion-selective layer and cation-selective layer. In this paper, a series of BPMs based on PTFE (polytetrafluoroethylene) reinforced QAPSF (quaternized polysulfone) and SPEEK (sulfonated poly ether ether ketone) are prepared and investigated for the VRB application. As expected, all the membranes have presented typical sandwiched structure with an obvious intermediate layer observed by SEM. Owing to the “Donnan exclusion effect” of anion groups in QAPSF, all the BPMs have shown very low VO2+ permeability. Particularly, the battery with Q/P/S-3:2 membrane has shown average coulombic efficiency of 98.9% at current density of 40–80 mA cm−2. Considering the simple adjustment and abundant choice of cation or anion resins, BPMs membranes should be a promising candidate for VRB application after further investigation.

Fluoro-methyl sulfonated poly(arylene ether ketone-co-benzimidazole) amphoteric ion-exchange membranes for vanadium redox flow battery

In this work, amphoteric ion-exchange membranes (AIEMs) prepared from fluoro-methyl sulfonated poly(arylene ether ketone-co-benzimidazole)s have been systematically evaluated for their potential usage in all vanadium redox battery (VRB). Our investigation has demonstrated that the compacted structure originated from the self-assembly ionic cross-linking and the positive charged benzimidazole moiety in AIEM matrix could synergistically reduce the vanadium species cross-contamination. The self-discharge time of a single cell assembled with AIEM of optimized chemical structure is over 3 times longer than that with Nafion117, and a desirable conductivity/permeability trade-off can be achieved by tuning the content of benzimidazole moiety. Single cell assembled with the optimized AIEM exhibit higher battery efficiencies and lower capacity loss than that with Nafion117 at current densities of 30, 50 or 70 mA cm−2. Furthermore, the AIEMs are able to tolerate the strong oxidizing VO2+ and remain intact for over 370 days, as revealed from ex-situ chemical stability tests. These findings strongly suggest that the as-prepared AIEM can be a good candidate for low-cost and high-performance separator in VRB application.

Tackling capacity fading in vanadium flow batteries with amphoteric membranes

Capacity fading and poor electrolyte utilization caused by electrolyte imbalance effects are major drawbacks for the commercialization of vanadium flow batteries (VFB). The influence of membrane type (cationic, anionic, amphoteric) on these effects is studied by determining the excess and net flux of each vanadium ion in an operating VFB assembled with a cation exchange membrane (CEM), Nafion® NR212, an anion exchange membrane (AEM), Fumatech FAP-450, and an amphoteric ion exchange membrane (AIEM) synthesized in-house. It is shown that the net vanadium flux, accompanied by water transport, is directed towards the positive side for the CEM and towards the negative side for the AEM. The content of cation and anion exchange groups in the AIEM is adjusted via radiation grafting to balance the vanadium flux between the two electrolyte sides. With the AIEM the net vanadium flux is significantly reduced and capacity fading due to electrolyte imbalances can be largely eliminated. The membrane's influence on electrolyte imbalance effects is characterized and quantified in one single charge-discharge cycle by analyzing the content of the four different vanadium species in the two electrolytes. The experimental data recorded herewith conclusively explains the electrolyte composition after 80 cycles.

Amphoteric Ion-Exchange Membranes with Significantly Improved Vanadium Barrier Properties for All-Vanadium Redox Flow Batteries.

All-vanadium redox flow batteries (VRBs) have attracted considerable interest as promising energy-storage devices that can allow the efficient utilization of renewable energy sources. The membrane, which separates the porous electrodes in a redox flow cell, is one of the key components in VRBs. High rates of crossover of vanadium ions and water through the membrane impair the efficiency and capacity of a VRB. Thus, membranes with low permeation rate of vanadium species and water are required, also characterized by low resistance and stability in the VRB environment. Here, we present a new design concept for amphoteric ion-exchange membranes, based on radiation-induced grafting of vinylpyridine into an ethylene tetrafluoroethylene base film and a two-step functionalization to introduce cationic and anionic exchange sites, respectively. During long-term cycling, redox flow cells containing these membranes showed higher efficiency, less pronounced electrolyte imbalance, and significantly reduced capacity decay compared to the cells with the benchmark material Nafion 117.

A novel amphoteric ion-exchange membrane prepared by the pore-filling technique for vanadium redox flow batteries

A novel amphoteric ion-exchange membrane (AIEM) was prepared through the pore-filling technique, for vanadium redox flow battery (VRBs) applications.

Ultra-low vanadium ion diffusion amphoteric ion-exchange membranes for all-vanadium redox flow batteries

An amphoteric ion-exchange membrane (AIEM) from fluoro-methyl sulfonated poly(arylene ether ketone) bearing content-controlled benzimidazole moiety, was firstly fabricated for vanadium redox flow battery (VRB). The AIEM and its covalently cross-linked membrane (AIEM-c) behave the highly suppressed vanadium-ion crossover and their tested VO2+ permeability are about 638 and 1117 times lower than that of Nafion117, respectively. This is further typically verified by the lower VO2+ concentration inside AIEM that is less than half of that inside Nafion117 detected by energy dispersive X-ray spectrometry, in addition of the nearly 3 times longer battery self-discharge time. The ultra-low vanadium ion diffusion could be ascribed to the narrower ion transporting channel originated from the acid-base interactions and the rebelling effect between the positively-charged benzimidazole structure and VO2+ ions. It is found that, VRB assembled with AIEM exhibits the equal or higher Coulombic efficiency (99.0% vs. 96.4%), voltage efficiency (90.7% vs. 90.7%) and energy efficiency (89.8% vs. 87.4%) than that with Nafion117 and keeps continuous 220 charge–discharge cycles for over 25 days, confirming that the AIEM of this type is a potentially suitable separator for VRB application.

Novel amphoteric ion exchange membranes by blending sulfonated poly(ether ether ketone)/quaternized poly(ether imide) for vanadium redox flow battery applications

For vanadium redox flow battery (VRB) applications, novel amphoteric ion exchange membranes (AIEMs) are prepared using sulfonated poly(ether ether ketone) (SPEEK) and quaternized poly(ether imide) (QAPEI) by a facile method.

Study of Chemical Modified Amphoteric Ion Exchange Membrane from Taurine

Fluorinated poly(aryl ether oxadiazole), synthesized by the copolymerization of 2,5-bis(2,3,4,5,6-pentafluorophenyl)-1,3,4-oxadiazole and diallylbisphenol A, was used as the main polymer chain (MP). 2-aminoethanesulfonic acid (taurine) was attached to brominated-MPs (Br-MPs) at mild conditions, serving as both cation and anion exchange groups. AIEM-0.6, AIEM-1.4 and AIEM-2.0 were obtained via solution-casting method. Quantum calculation and experiments verified the selective permeability of the membranes: high proton conductivities and low vanadium permeation parameters. Also the AIEMs demonstrate good acid resistance and thermal stability, showing potential in vanadium redox flow battery (VFB) fields.

Amphoteric ion exchange membrane synthesized by direct polymerization for vanadium redox flow battery application

Novel sulfonated poly (fluorenyl ether ketone) with pendant quaternary ammonium groups (SPFEKA) was successfully synthesized by one-pot copolymerization of bis(4-fluoro-3-sulfophenyl)sulfone disodium salt, 4,4′-difluorobenzophenone, bisphenol fluorene and 2,2′-dimethylaminemethylene-9,9′-bis(4-hydroxyphenyl) fluorene (DABPF). The chemical structures were confirmed by FT-IR, and 1H NMR. The thermal properties were fully investigated by TGA. The synthesized copolymers SPFEKAs are soluble in aprotic solvents, and can be cast into membranes on a glass plate from their N,N′-dimethylacetamide (DMAc) solution. A new kind of amphoteric ion exchange membrane (AIEM) was obtained by immersed SPFEKA into 1 M sulfuric acid. The proton conductivities of these membranes are comparable to the most reported sulfonated polymers under the same conditions. The permeability of vanadium ions in vanadium redox flow battery (VRB) was effectively suppressed by introducing quaternary ammonium groups for Donnan exclusion effect. AIEM-20% possess a only 4.4% vanadium ion permeability of Nafion 115. Cell performance tests showed that the VRB assembled with AIEM-20% shows the highest coulombic efficiency (CE) at the current density of 50 mA/cm2, because of its lowest VO2+ permeability. In conclusion, these ionomers could be promising candidates for ion-exchange membranes for VRB applications.

Facile synthesis of amphoteric ion exchange membrane by radiation grafting of sodium styrene sulfonate andN,N-dimethylaminoethyl methacrylate for vanadium redox flow battery

Sodium styrene sulfonate (SSS) and N,N-dimethylaminoethyl methacrylate (DMAEMA) are grafted into poly(vinylidene difluoride) (PVDF) film using γ-radiation techniques. SSS could be co-grafted successfully with DMAEMA, although it is difficult to be grafted solely into PVDF films. Through subsequent protonation process, an amphoteric ion exchange membrane (AIEM) is synthesized facilely and environmentally benignly. The degree of grafting (DOG) increases with absorbed dose and levels off at 40 kGy. Micro-FTIR and X-ray photoelectron spectroscopy analyses confirm the existence of the designed units and quaternization of DMAEMA units in the grafted films. The quaternization and grafting occurring at the same time makes it a unique way to synthesize quaternized AIEM in one step. Finally, an AIEM with a DOG of 43% is assembled in the vanadium redox flow battery (VRFB) system, and the VRFB maintains an open circuit voltage higher than 1.4 V after placed for 85 h, which is much longer than that with Nafion117 membrane. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5194–5202

Designing a new process to prepare amphoteric ion exchange membrane with well-distributed grafted chains for vanadium redox flow battery

A combination of radiation grafting technique and solution phase inversion method has been successfully utilized to prepare amphoteric ion exchange membranes (AIEMs) from poly(vinylidene fluoride) (PVDF) powder. First, styrene (St) and dimethylaminoethyl methacrylate (DMAEMA) were grafted into PVDF powder via radiation-induced graft copolymerization. Subsequently, the grafted powder was transferred into film by casting method. Finally the AIEM was obtained by sulfonation and protonation of the grafted film. Micro-FTIR, XPS and TG analyses testified that the grafting and sulfonation of St and DMAEMA units in poly(St-co-DMAEMA) grafts had been carried out as designed. SEM-EDX image of the AIEM indicates the well distribution of the grafted chains across the AIEM. The physicochemical properties of the resulting AIEMs and the conventional AIEMs based PVDF film grafting were comparatively investigated. The AIEMs obtained by this novel process were found to have superior conductivity compared with the AIEMs based PVDF film grafting. Open circuit voltage measurements showed that the vanadium redox flow battery (VRFB) assembled with this new AIEM maintained the value above 1.3 V after a period of 30 h, which was much longer than that with the Nafion117 membrane, suggesting this approach is effective for imparting preferable structure-properties to the membrane for VRFB.

A novel amphoteric ion exchange membrane synthesized by radiation-induced grafting α-methylstyrene and N,N-dimethylaminoethyl methacrylate for vanadium redox flow battery application

Abstract A novel amphoteric ion exchange membrane (AIEM) was synthesized by radiation-induced grafting α-methyl styrene (AMS) and dimethylaminoethyl methacrylate (DMAEMA) into poly(vinylidenedifluoride) (PVDF) films, followed by sulfonation and protonation processes. The monomer AMS could be co-grafted successfully with DMAEMA in the presence of AlCl 3 although it was difficult for AMS to be grafted solely into PVDF films. The grafting yield ( GY ) increased with absorbed dose up to about 40 kGy. It was found that the ratio of DMAEMA to AMS in the poly(DMAEMA- co -AMS) grafts changed slightly with various monomer ratio of DMAEMA to AMS in the feed by elemental analysis. The Micro-FTIR and XPS analyzes testified that the AIEM had been prepared as designed. The AIEM with a GY of 40% showed similar conductivity, higher IEC and lower permeability of vanadium ions compared with Nafion117 membrane. The vanadium redox flow battery (VRFB) assembled with the AIEM of 41.1% GY maintained an open circuit voltage higher than 1.4 V after placed for 60 h, which was much longer than that with the Nafion117 membrane. Therefore, it is expected to be excellent candidate for the application of VRFB.

Performance of vanadium redox flow battery with a novel amphoteric ion exchange membrane synthesized by two-step grafting method

A novel ETFE-based amphoteric ion exchange membrane (AIEM) was prepared through a two-step radiation-induced grafting technique. ETFE film was first grafted with styrene (St) (denoted as ETFE- g-PS), followed with a sulfonation treatment to obtain a cation exchange membrane (ETFE- g-PSSA). The ETFE- g-PSSA membrane was subsequently grafted with dimethylaminoethyl methacrylate (DMAEMA) and then protonated, resulting in an AIEM with both anionic and cationic groups. The grafting yields ( GY) in the above two steps increased with absorbed dose and leveled off at about 30 kGy and 20 kGy, respectively. Micro-FTIR and XPS analyses testified that the AIEM had been prepared as designed. The obtained AIEM exhibited high ion exchange capacity ( IEC) and conductivity, as well as significantly reduced permeability of vanadium ions. Vanadium redox flow battery (VRFB) assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.3 V after placed for 300 h, and exhibited higher columbic efficiency and energy efficiency than that with Nafion 117 membrane.

Amphoteric ion exchange membrane synthesized by radiation-induced graft copolymerization of styrene and dimethylaminoethyl methacrylate into PVDF film for vanadium redox flow battery applications

Poly(vinylidene difluoride) (PVDF) film was grafted with styrene (St) and dimethylaminoethyl methacrylate (DMAEMA) using γ-irradiation techniques. Through subsequent sulfonation and protonation processes, a new kind of amphoteric ion exchange membrane (AIEM) was synthesized. The grafting yield ( GY) increased with absorbed dose and leveled off at about 60 kGy. The composition of poly(St- co-DMAEMA) grafts was correlated to the ratio of St to DMAEMA monomer in the feed. Micro-FTIR and XPS analyses testified that the grafting and sulfonation of St unit in poly(St- co-DMAEMA) grafts had been carried out as designed. Further characterizations showed that the properties of the AIEM strongly depended on the composition and GY of the film, i.e. higher content of DMAEMA brought lower permeability of vanadium ions and conductivity, while higher GY led to higher water uptake, ion exchange capacity ( IEC) and conductivity. Finally, an AIEM with a GY of 26.1% was assembled and tested in the vanadium redox flow battery (VRFB) system. It was found that the VRFB assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.2 V after placed for 68 h, which was much longer than that with the Nafion117 membrane. Therefore, this work provides a novel method to develop potential substitute of Nafion membranes to be applied in VRFB system.

Transport of pharmaceuticals through silk fibroin membrane

The transport of pharmaceuticals through silk fibroin membranes has been investigated. The membrane was prepared from Chinese cocoon. The permeability coefficients of five kinds of pharmaceutical, i.e. 5-fluorouracil (5FU), l-(+)-ascorbic acid (Vc), resorcinol (Res), sodium phenolsulfonate (SPS) and benzyltri-methylammonium chloride (BTAC), were measured in the pH range from 3.0 to 9.0. The silk fibroin membrane was an amphoteric ion-exchange membrane composed of both weak acidic and weak basic groups. Membrane-potential measurements revealed that the isoelectric point of the membrane was about pH 4.5. The positively charged pharmaceutical, BTAC, was excluded from the membrane below the isoelectric point. On the other hand, the negatively charged one, SPS, had a permeability that decreased as the pH increased. The neutral molecule, Res, however, penetrated through the membrane independently of pH value over the measured pH range. In the case of 5FU and Vc, the permeability coefficients decreased steeply above pH7 and pH4, respectively, because 5FU and Vc were negatively charged above pH7 (p K a=8.0) and pH 4 (p K a=4.25), respectively.

Study of Ion Transport across Amphoteric Ion-Exchange Membrane. VI. Multi-Ionic Potential, Membrane Permeability, and Ion-Sieve Effect

Abstract The transport characteristics of an amphoteric ion-exchange membrane were examined by electrochemical measurements for a multi-ionic system, in which NH4Cl and tetraalkylammonium chloride (TAA·Cl) solution phases are divided by the membrane phase. Membrane permeability values were estimated for two cations, NH4+ and TAA+, and Cl−, as well as for whole cations as an averaged quantity describing the cation transport process relative to the anion transport process. The present study indicated that ion-sieve permeation characteristics, which have been demonstrated as a fundamental transport mechanism across an amphoteric ion-exchange membrane in the concentration-cell systems, still play a dominant role in the multi-ionic system. Satisfactory linear relationships of the logarithmic membrane permeabilities to NH4+, Cl−, and a series of TAA+ ions against the hydrated ionic radii of respective ions were obtained. This linear relation was not affected appreciably by the combination of electrolytes separated by the membrane. Thermodynamic analyses on the multi-ionic transport across an amphoteric ion-exchange membrane contribute to improve the selective performances of membrane materials and to survey more efficient operating conditions of the membrane processes.

Membrane Potential of Weak Amphoteric Polymer Membrane Composed of Silk Fibroin.

Silk fibroin membrane is the amphoteric ion exchange membrane with the weak acid and base which are composed of amino and carboxyl groups, respectively. In this study ion transport phenomena were investigated using Teorell-Meyers-Sievers (TMS) theory. Membrane potential was measured for KCl, K2SO4, K2HPO4, MgCl2, CaCl2, and MgSO4 aqueous solution. The effective charge density (QCx) and ion mobility ratio of anion to cation (ω-/ω+) in the membrane were calculated by applying TMS theory to experimental results. QCx, was 0.015mol/L, which was one-nineteenth times smaller than that calculated from the data of amino acid content in silk fibroin. ω-/ω+of KCl, CaCl2 and MgCl2 in the membrane were larger than that in water, and ω-/ω+of K2SO4, K2HPO4, and MgSO4were smaller than that in water.

Transport number of an ion across an amphoteric ion-exchange membrane in CaCl 2NaCl system

In an amphoteric membrane-mixed electrolyte system, the ionic concentration within the membrane and the membrane conductance were measured. The additivity concept proposed in our previous paper [J. Membrane Sci, 48 (1990) 25] was applied to the present mixed electrolyte system and each ion transport number in the mixed system was estimated. The transport number of Ca 2+, t Ca, was larger than t Na in the whole range concentration and decreased with increasing concentration of the outer electrolyte solution. Additionally, to ascertain whether the predicted values are reasonable, electrodialysis in the mixed electrolyte system was carried out under the same experimental conditions. The transport numbers estimated in the mixed electrolyte system were approximately in good agreement with the values obtained from the electrodialysis experiments. Furthermore, the transport numbers for two different ionic states in the membrane were evaluated and the concentration dependence of the total transport number, t M, was discussed on the basis of the results.