Amphoteric Ion Exchange Membrane Research Articles

The effect of polymer with tunable alkyl spacers on the microstructure of amphoteric membrane for vanadium redox flow battery (VRB)

Amphoteric membranes, as promising candidates for VRBs, have attracted more attention. The side-chain-type polymers go far towards improving ion exchange capacity and further enhancing ion conductivity. A kind of Amphoteric ion exchange membranes (AIEMs) with different alkyl chain lengths (C2, C6, and C12 spacers) were synthesized by using ring-opening metathesis polymerization (ROMP). In addition, the interactions between N-containing groups with positively charged and -SO3- groups prevent swelling and vanadium crossover. The microphase separation structure through side chain induction was regulated, to respond to the ionic mobility of the membrane. The effect of the spacer lengths on the ion selectivity of AIEMs is investigated. In addition, the size and matrix of the constructed ion channel were calculated by using coarse-grained molecular dynamics (CGMD) simulation, which further verified the experiment.

The endowment of monovalent anion selectivity and antifouling property to cross-linked ion-exchange membranes by constructing amphoteric structure

Ion exchange membranes (IEMs) with high monovalent-ion selectivity show promising application in ion resource recovery. In this work, we report a kind of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based on amphoteric ion exchange membranes (AIEMs) having cross-linked structure. Therein, four imidazolium-terminated aliphatic chains (2IM-nC, n = 3, 6, 9, and 12) with varied number of −CH2− were used as crosslinker for cross-linking membrane matrix. Small-angle X-ray scattering tests indicate that the ion cluster sizes of the four AIEMs are evaluated with values of 0.378, 0.384, 0.388 to 0.408 nm, which possibly render the enhanced mono-valent anion selectivity of as-prepared AIEMs. Tested in the electrodialysis (ED) filled with a mixture solution of 0.05 M NaCl + 0.05 M Na2SO4, at current densities of 2.5 mA·cm−2 and 5.0 mA·cm−2, the PSO42-Cl- values of cross-linked AIEM having longer alkyl chains are 20.41 and 22.51, respectively, which are higher than AIEM with shorter cross-linker alkyl chain under the same conditions (3.5). Due to the hydrophilic surface and hydrophilic/negatively charged zwitterionic surface of AIEM, act as useful barriers via physical blocking and electrostatic repulsion, respectively, the anti-fouling performance of IEMs is improved simultaneously. In view of the superior performance, it is believed that the structure–property relationship of AIEM developed here can serve as a guideline for advanced IEMs.

Enhanced monovalent anion selectivity of poly(2,6-dimethyl-1,4-phenylene oxide)-based amphoteric ion exchange membranes having rough surface

Amphoteric polyelectrolytes have been used as the materials for the high-performance ion-exchange membranes applied in redox flow battery and electrodialysis (ED) etc. In this work, four amphoteric ion-exchange membranes (AIEMs) based on sodium 1-propanesulfonate-3-methylimidazole (MIm-PS) and 1-butylimidazole (BIm) decorated poly(2,6-dimethyl-1,4-phenylene oxide) have been prepared for mono-/bi-valent anion separation by using the electrodialyzer. The optimized AIEM has a low surface area resistance of 5.79 Ω⋅cm2. During the ED testing, at 2.5 mA⋅cm−2, the perm-selectivity (PSO42−Cl−) tested in a binary mixture of 0.05 M NaCl and 0.05 M Na2SO4, achieves the value of 16.12 at 30th min, which is significantly higher than that of anion-exchange membrane (1.68) as the reference. This superior separation performance has been further verified by the perm-selectivity of 55.5, tested in a single solution of 0.05 M NaCl or 0.05 M Na2SO4. The high perm-selectivity results from the electrostatic repulsion difference of mono-/bi-valent ions against the negatively-charged –SO3– groups, accompanying with pore-size sieving effect resulting from the smaller ion cluster space of 0.261 nm. It is interesting to find that AIEMs show the increased ion flux values of Cl−/SO42−, though the presence of the negatively-charged –SO3− groups, which is possibly related to the convex particle-like surface that increasing the effective surface area for ions passing. This work may provide a reference to guide the architectural design of advanced monovalent anion-selective IEMs.

Enhanced Monovalent Anion Selectivity of Poly(2,6-Dimethyl-1,4-Phenylene Oxide)-Based Amphoteric Ion Exchange Membranes Having Rough Surface

Enhanced Monovalent Anion Selectivity of Poly(2,6-Dimethyl-1,4-Phenylene Oxide)-Based Amphoteric Ion Exchange Membranes Having Rough Surface

Enhanced Monovalent Anion Selectivity of Poly(2,6-Dimethyl-1,4-Phenylene Oxide)-Based Amphoteric Ion Exchange Membranes Having Rough Surface

Enhanced Monovalent Anion Selectivity of Poly(2,6-Dimethyl-1,4-Phenylene Oxide)-Based Amphoteric Ion Exchange Membranes Having Rough Surface

Preparation of sulfonated poly（ether ether ketone） amphoteric ion exchange membrane and its application in iron-chromium redox flow battery

Preparation of sulfonated poly（ether ether ketone） amphoteric ion exchange membrane and its application in iron-chromium redox flow battery

Polymer Membranes for All-Vanadium Redox Flow Batteries: A Review.

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research which aim to enable more environmentally friendly energy conversion, especially for stationary applications. As a critical component of the electrochemical cell, the membrane influences battery performance, cycle stability, initial investment and maintenance costs. This review provides an overview about flow-battery targeted membranes in the past years (1995–2020). More than 200 membrane samples are sorted into fluoro-carbons, hydro-carbons or N-heterocycles according to the basic polymer used. Furthermore, the common description in membrane technology regarding the membrane structure is applied, whereby the samples are categorized as dense homogeneous, dense heterogeneous, symmetrical or asymmetrically porous. Moreover, these properties as well as the efficiencies achieved from VRFB cycling tests are discussed, e.g., membrane samples of fluoro-carbons, hydro-carbons and N-heterocycles as a function of current density. Membrane properties taken into consideration include membrane thickness, ion-exchange capacity, water uptake and vanadium-ion diffusion. The data on cycle stability and costs of commercial membranes, as well as membrane developments, are compared. Overall, this investigation shows that dense anion-exchange membranes (AEM) and N-heterocycle-based membranes, especially poly(benzimidazole) (PBI) membranes, are suitable for VRFB requiring low self-discharge. Symmetric and asymmetric porous membranes, as well as cation-exchange membranes (CEM) enable VRFB operation at high current densities. Amphoteric ion-exchange membranes (AIEM) and dense heterogeneous CEM are the choice for operation mode with the highest energy efficiency.

Novel amphoteric ion exchange membranes by blending sulfonated poly(ether ether ketone) with ammonium polyphosphate for vanadium redox flow battery applications

AbstractA novel amphoteric ion exchange membrane for vanadium redox flow battery (VRFB) was explored by blending sulfonated poly(ether ether ketone) (SPEEK) and ammonium polyphosphate (APP). The high‐stability flame retardant of cross‐linked APP with a large number of NH4+ groups was first introduced into SPEEK membrane. It was observed that the addition of APP with special structure could achieve a good balance between proton conductivity and vanadium ions permeability. The abundant NH4+ in APP could block the penetration of vanadium ions by Donnan/Manning exclusion effect and ionic crossing networks due to the ionic bonds between cation and anion groups, and specially a small amount of APP within 5% could remarkably improve the proton conductivity of pristine SPEEK membrane might be ascribed to the unique fast proton transport channels formed by hydrogen bond networks and particular micro‐phase separation as a result of interaction between SPEEK and APP. When 5% APP was blended, the SPEEK/APP‐5% (S/APP‐5%) amphoteric membrane showed a higher selectivity of 20.87 × 104 S min/cm3 (with a good proton conductivity of 0.075 S/cm and a lower VO2+ permeability of 3.45 × 10−7 cm2/ min) and presented better thermal and chemical stability compared to Nafion115 and SPEEK membranes. The VRFB single cell assembled with S/APP‐5% amphoteric membrane exhibited more excellent performance than that of Nafion115 and pristine SPEEK membranes, which revealed a higher coulombic efficiency of 96.3%–98.3%, comparable voltage efficiency of 88.4%–78.7% and higher energy efficiency of 85.1%–77.4% from 40 to 80 mA/cm2, respectively, and showed relatively good stability of the efficiency up to 50 cycles at 60 mA/cm2. The results demonstrated that the designed S/APP amphiprotic membrane of outstanding selectivity, high battery efficiency, and good durability is a prospected VRFB separator.

Bi-functional side chain architecture tuned amphoteric ion exchange membranes for high-performance vanadium redox flow batteries

The blended amphoteric membranes possessed a reducing cation exchange capacity with increasing the anion exchange capacity. Bi-functional side-chain-type polymers are conducive to have both high cation exchange capacity and high anion exchange capacity at the same time, and further enhance ion conductivity of amphoteric ion exchange membranes (AIEMs). Herein, novel side-chain type AIEMs are prepared via ring-opening metathesis polymerization of norbornene possessing the advantages of yielding easily modified molecular architectures, simple and controllable polymerization, and producing the membranes with high chemical stability. To avoid the occurrence of excess water swelling arising from the increased zwitterionic groups, hydrophobic spacers (alkyl chain-(CH2)6 -) were introduced to be situated between the aromatic main chain and ionic groups. This unique structure favors ion clusters to be aggregated and thus forms highly ordered water channels so that the protons can be efficiently transported along the center of channels and possess excellent proton conductivity. In addition, the ion crosslinking interactions enhance the mechanical stability of AIEMs. The resultant AIEM (1/2) exhibits a higher ion conductivity of 7.58 × 10-2 S cm-1 and vanadium ion permeability of 0.21 × 10-9 cm2 s-1 at room temperature. Based on these good properties, the vanadium redox flow batteries (VRBs) with prepared membranes and Nafion 212 were tested. The energy efficiency (EE) of VRBs with AIEM (1/2) still reaches 84.76% at the current density of 160 mA cm-2, which is better than that with Nafion 212 (76.26%). Moreover, the EE of VRBs with AIEM (1/2) is 82.11% after 200 cycles, indicating that the prepared membranes possess a good stability.

The effect of counter-ion substitution on poly(phthalazinone ether ketone) amphoteric ion exchange membranes for vanadium redox flow battery

The study proposed a novel method to prepare poly(phthalazinone ether ketone) amphoteric ion exchange membranes (Q/S-M) with both increased efficiency and chemical stability for vanadium redox flow battery (VRB) applications. Q/S-M membranes were obtained after the successive amination and acidification process of blend base membranes prepared from brominated poly(phthalazinone ether ketone) (BPPEK) and sulfonated poly(phthalazinone ether ketone) substituted by counter-ions (SPPEK-M), where M was defined as counter-ions: Li+, Na+ and K+. The study analyzed the effect of counter-ion size on properties of Q/S-M membranes, which were compared with those for Q/S membrane obtained from BPPEK and SPPEK in acid form. Q/S and Q/S-M membranes maintained the same composition of ionic groups. The Q/S-M membranes induced by bigger counter-ion size showed the increasing of water content and ion diffusion rate, which was higher than that of Q/S membrane. Related to Q/S membrane, Q/S–K membrane possessed almost half area resistance (0.67 Ω cm2 vs 1.43 Ω cm2), and the value was close to that of Nafion115. Q/S-M membranes exhibited a 96.0–98.8% decrease in VO2+ permeability over Nafion115. Q/S–K membrane displayed a 6.5% increase in VE and correspondingly a 6.2% increase in EE over Q/S membrane, maintaining superior EE than Nafion115 (89.7% vs 86.5%). The ex-situ degradation test in VO2+ solutions indicated that despite close EE, Q/S–K membrane showed superior chemical stability over amphoteric ion exchange membranes (AIEMs) in our previous works. There was no obvious efficiency decay of Q/S–K membrane during 100-cycles test, indicating the good duration in operating VRB.

Investigation of poly(phthalazinone ether ketone) amphoteric ion exchange membranes in vanadium redox flow batteries

Amphoteric ion exchange membranes (Q-x/S) for vanadium redox flow battery (VRFB) are prepared from brominated poly(phthalazinone ether ketone) with the degree of substitution (DS) in the range of 60–95% and sulfonated poly(phthalazinone ether ketone) through blending and amination reaction, and x refers to the DS. Q-x/S membranes contain quaternary ammonium and sulfonic groups, making it easy to adjust the permeability of different vanadium ions and net water transport. When the DS increases from 60 to 95%, the discrepancy of the permeability for VO2+/VO2+ and V2+/V3+ enhances. The permeability of VO2+, VO2+, V3+ and V2+ for Q-x/S membranes was 98.7–99.9%, 98.6–99.9%, 99.5–99.9% and 99.2–99.9% less than those for Nafion115. Compared to Nafion115, Q-88/S membrane shows 81.3 and 84.8% decrease in static and cycling water transport volume. The energy efficiency (EE) of Q-88/S and Q-95/S membranes reaches 90% at the current density of 40 mA cm−2, higher than that of Nafion115 (86.5%). Compared with Nafion115, Q-x/S membranes exhibit stable efficiencies and higher capacity retention in long-term VRFB operation. Low vanadium permeability and net water transport volume make Q-x/S membranes promising to be used in commercial VRFB.

Design and Development of an Innovative Barrier Layer in Vanadium Redox Flow Batteries

Vanadium Redox Flow Battery (VRFB) is an electrochemical energy storage technology that exploits red-ox reactions of vanadium ions dissolved in acidic solutions to convert electrical energy into and from chemical energy. VRFB is an interesting and promising technology because of its high efficiency, independent energy to power ratio, high flexibility and long cycle life [1]. However, VRFB commercialization is still hindered by some technological issues, among which is the capacity loss induced by the undesired transport of vanadium ions across the ion-exchange membrane. Depending on the nominal operating condition, the choice of suitable membrane for VRFB application results from the trade-off between low vanadium permeability and high proton conductivity.Nafion® is widely used in VRFB: it presents high conductivity and good mechanical and chemical stability, but it is not ideally selective towards vanadium ions. This implies the adoption of thicker membrane to limit capacity loss, leading to increased ohmic loss and system costs [2]. Alternative cation exchange membranes (CEMs) are SPEEK or SPI that are promising because of their reduced permeability, but the low conductivity and stability hinder their competitiveness with respect to Nafion®. Anion exchange membranes (AEMs) are interesting alternatives, but the poor chemical stability and low conductivity limit their application in VRFB. Amphoteric ion exchange membranes (AIEM) combine the functional groups of both CEM and AEM, obtaining both low permeability and good conductivity. However, the complex preparation results in high costs [3].In this work, an additional selective layer, described in the patent WO 2019/197917, was deposited on a commercial cation exchange membrane. The selective layer, termed as barrier, is a porous component in which pores size, tortuous path, thickness and the composition are designed to improve layer selectivity towards vanadium ions. The barrier was manufactured with reactive spray deposition technology (RSDT), which is a flame-based synthesis process unique to Dr. Radenka Maric’s research group. Fabrication of the barrier layer by RSDT is a one-step process in which carbon-rich particles are synthesized in the flame and a mixture of commercial carbon black particles and ionomer is sprayed directly onto the membrane. In this work different barrier morphologies have been designed, manufactured and tested.The barrier layer was tested in a 25 cm2 cell during cycles at constant capacity in both charge and discharge [4]. After each charge and discharge step the cell was kept in OCV for 90 seconds in order to acquire cell OCV and get an insight into battery state of charge (SoC). Figure 1 reports the evolution of SoC after each step of charge: it is worth noting that the VRFB with barrier presents a significant reduction of SoC decay (i.e., capacity loss) compared to a reference VRFB employing Nafion® 115. Moreover, the VRFB with barrier exhibits a slightly higher efficiency and a good stability in time.In addition to electrochemical testing, the structure of the barrier layer was characterized using TEM, SEM and nitrogen adsorption. TEM and nitrogen adsorption provide information on pore structure and pore-size distribution, which can be related to the performance of the barrier layer during cell testing, while SEM shows that the coating is uniform in thickness and consistent from sample to sample.

Amphoteric blend ion-exchange membranes for separating monovalent and bivalent anions in electrodialysis

It is of significant importance to develop highly monovalent anion-selective membranes (MASM) having stable structure for a wide range of applications. To realize the efficient monovalent/bivalent anion separation, in this work, three amphoteric ion-exchange membranes (AIEMs) through blending were fabricated for use in electrodialysis (ED). The three membranes were prepared by blending amino-containing poly(arylene ether sulfone) (PAES-NH2) with 10, 15, and 20 wt% of sulfonated polysulfone (SPSf), respectively, followed by grafting imidazolium salt-terminated side alkyl chains on PAES backbone. Our investigations demonstrate that each transparent AIEM shows good miscibility between the two components, which has been verified by a homogeneous structure via SEM observation and by an even distribution of N element via EDX mapping. In the ED process at a current density of 2.5 mA cm−2, AIEM with 15 wt% of SPSf shows the superior perm-selectivity (Cl–/SO42–) of 21.8, relative to many reported MASMs having modified surfaces (<6.0), which is synergistically contributed by (i) electrostatic repulsion difference from the negatively-charged sulfonate groups against monovalent Cl– ions and bivalent SO42– ions and (ii) hydrated energy difference of hydrated Cl–/SO42– ions. This work thus presents a strategy to guide the architectural design of advanced MASMs.

Cross-linked amphoteric membrane: Sulphonated poly(ether ether ketone) grafted with 2,4,6-tris(dimethylaminomethyl)phenol using functionalized side chain spacers for vanadium redox flow battery

Herein, we report a novel synthesis of sulphonated poly(ether ether ketone) (SPK) grafted with 2,4,6-tris(dimethylaminomethyl)phenol (TAP) for preparation of amphoteric ion-exchange membrane (AIEM). Cross-linking has been achieved by using di-bromo alkane with different number of carbon chains (C6 & C10), and different AIEMs are assessed for vanadium redox flow battery (VRFB). These AIEMs are architected to contain –SO3H groups maintained conductivity, while –NH3+ groups for reduction in vanadium permeability with improve charge-discharge time via acid-base interactions. Structural and surface morphology of AIEMs have been elucidated by different spectral techniques (FTIR, 1H NMR, SEM, and AFM). Cross-linking and acid-base interactions effectively reduced water uptake, swelling ratio, VO+2 permeability and improved ion-exchange capacity, conductivity, along with membrane stabilities. Due to good synergy between conductivity and VO+2 permeability, cross-linked AIEM with six number of carbon chains (CQSPK-6) exhibited higher Coulombic (CE: 98.4% vs 91.2%) and energy efficiency (81.4% vs~76%) than Nafion 117 membrane at 60 mA cm−2 in single cell VRFB. Further, CQSPK-6 AIEM maintained stable performance during in-situ cycle test (100 cycles) at 60 mA cm−2. Hence, AIEM based on cross-linked SPK grafted with high molality of functional groups via side chain spacer is a promising candidate for an efficient VRFB system.

Poly(phthalazinone ether ketone) Amphoteric Ion Exchange Membranes with Low Water Transport and Vanadium Permeability for Vanadium Redox Flow Battery Application

Compact and homogeneous amphoteric ion exchange membranes (Q/S-AIEMs) without acid–base interaction for vanadium redox flow batteries (VRBs) are first prepared through a low-cost and simple way, in...

Amphoteric Ion Exchange Membranes Prepared by Preirradiation-Induced Emulsion Graft Copolymerization for Vanadium Redox Flow Battery.

A series of poly(vinylidene difluoride)-based amphoteric ion exchange membranes (AIEMs) were prepared by preirradiation-induced graft copolymerization of styrene and dimethylaminoethyl methacrylate in an aqueous emulsion media followed by solution casting, sulfonation, and protonation. The effects of absorbed dose and comonomer concentration on grafting yield (GY) were investigated. The highest GY of 44.5% at a low comonomer concentration of 0.9 M could be achieved. FTIR, TGA, and X-ray photoelectron spectroscopy (XPS) confirmed the successful grafting and sulfonation of the as-prepared AIEMs. Properties of the AIEMs such as water uptake, ion exchange capacity (IEC), ionic conductivity, and crossover behavior of VO2+ ions prepared by this novel technique were systematically investigated and compared with those of the commercial Nafion 115 membrane. It was found that at a GY of 28.4%, the AIEMs showed higher IEC and conductivity, lower permeability of VO2+ ions, and a longer time to maintain open circuit voltage than Nafion 115, which was attributed to their high GY and elaborate amphoteric structure. Consequently, this work has paved the way for the development of green and low-cost AIEMs with good performance for vanadium redox flow battery applications.

The Amphoteric Ion Exchange Membrane Based on CS/CMC for Tobacco-Protein Adsorption and Separation from Tobacco Extract

A macroporous amphoteric ion exchange membrane was prepared by blending chitosan (CS) and carboxymethylcellulose (CMC) in aqueous solution, with glutaraldehyde as a crosslinking agent and silica particles as porogens. The good compatibility between CS and CMC was confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy (FTIR-ATR). A scanning electron microscope was used to observe the morphology of CS/CMC blend membranes, in which a three-dimensional opening structure was formed, and no phase separation was discovered. Tobacco extract was used as a separation model to get tobacco protein. And the effects of the pH value, adsorption time, CS/CMC content, initial protein concentration, and CS/CMC composition on tobacco protein adsorption were investigated by coomassie blue staining during the adsorption process. The results showed that the maximum adsorption capacity of 271.78 mg/g can be achieved under the condition of pH 6.15, adsorption time of 8 h, initial protein concentration of 1.52 mg/mL, and CS/CMC weight of 0.05 g with a mass ratio of 80 : 20. Tobacco proteins were successfully separated from tobacco extract by adjusting the pH of the feed and the desorption solutions to change their electrostatic force. It was found that the high desorption capacity and protein desorption efficiency can be achieved at pH 9.40. The blend membranes also demonstrated good reusability after 3 adsorption-desorption cycles.

Preparation and properties of amphoteric ion exchange membrane for all vanadium redox flow batteries

The amphoteric ion exchange membrane basing on cheap polyetheretherketone (PEEK) engineering plastics was prepared by modification reactions and casting method in this investigation. The membrane was characterized by Fourier transformer infrared and thermogravimetric analysis. The IEC and sheet resistance of the membrane were also measured. The energy efficiency was tested by an experimental application device. Results show that the sulfonic acid and quaternary ammonium groups are introduced into the molecule chain successfully. The membrane has good thermal stability and IEC as high as 2.58 mol/kg, and the sheet resistance of which is 0.11 Ω/cm2. The energy efficiency of the membrane is 74.87%. The good properties and low price of the product in this investigation imply the large scale potential applications in VRFBs.

Facile Preparation of EVOH-Based Amphoteric Ion Exchange Membrane Using Radiation Grafting Technique: A Preliminary Investigation on Its Application for Vanadium Redox Flow Battery.

A novel amphoteric ion exchange membrane (AIEM) was successfully prepared by one-step radiation grafting of sodium styrene sulfonate (SSS) and dimethylaminoethyl methacrylate (DMAEMA) onto ethylene-vinylalcohol copolymer (EVOH) powder and sequent transferring into film by casting method. Fourier transform infrared spectrometry (FT-IR), thermal gravimetric analyzer (TGA) and elemental analysis testified SSS and DMAEMA were successfully grafted onto EVOH. The ion exchange capacity, water uptake and proton conductivity of the resulting AIEM increased with grafting yield (GY). At the GY of 40.9%, the permeability of vanadium ions of AIEM was 3.98 × 10−7 cm2 min−1, which was better than Nafion117 membrane. Furthermore, the cost of this AIEM is much lower than that of Nafion117 membrane. This work provided a low cost and simple method for fabrication of the ion exchange membrane for vanadium redox flow battery (VRFB). Meanwhile, it also provided a new direction for the application of EVOH.

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..