Anion Conductance Research Articles

Study of Alkaline Durability and Anion Conductivity Using New Expanded Pyridinium Polymer with Self-Assembly Ability

Polymer electrolyte fuel cells (PEFCs) are promising for practical use as the next generation clean power source. Since the anion exchange membrane fuel cell (AEMFC) operates in a basic environment, cost reduction is possible because non-platinum catalysts such as iron can be used. In addition, since the activation overpotential of oxygen reduction is smaller than that of a proton exchange membrane fuel cell (PEMFC), it is attracting attention as an alternative to PEMFC [1]. However, for practical use, further improvement of the anion conductivity and alkaline durability of the anion exchange membrane (AEM), in which a hydroxide ion (OH-) acts as an anion conductor is required. General strategy to promote anion conduction has been to move cation side chain freely, however problem is that the decomposition reaction occurs due to the attack from the OH-. In this research, a new strategy of “self-organizing cation units to form channel structure” is studied to improve alkaline durability and anion conductivity at the same time. It is considered that this self-assembly strategy can achieve both the low mobility of cation to suppress from OH- attack and the anion conduction path. To realize this concept, an extended pyridinium monomer was newly designed with reference to extended pyridinium, one of the heteropolycyclic aromatic cation. Since strong π-π interactions have been reported between extended pyridiniums, introducing an extended pyridinium into the polymer will suppress the molecular motion of the anion conduction site and will induce the formation of self-assembled channels. A new extended pyridinium monomer (TVP) was synthesized according to the synthesis method of the extended pyridinium salt of Katrizky et al [2]. Synthesized TVP was obtained as a pale yellow powder. From the 1H-NMR spectrum, vinyl group and aromatic peaks were observed, and it was confirmed that the monomer possessed high purity. The homopolymer (PTVP) was synthesized by free radical solution polymerization of TVP. Synthesized PTVP was obtained as a yellow solid. In 1H-NMR measurement, vinyl peaks were disappeared and the broadening of aromatic ring peaks were observed, suggesting that the free radical polymerization was taken place. Since PTVP is brittle and difficult to use as a film probably due to its rigid molecular structure, the introduction of a copolymer monomer was examined. When styrene and isoprene reported as an anion exchange membrane were examined as a copolymerization monomer, copolymer of PTVP-styrene and PTVP-isoprene were obtained, respectively. Although a PTVP-styrene copolymer film was brittle, a PTVP-isoprene copolymer film was obtained as a free standing film. Alkaline stability and anion conductivity of the films will be discussed. [1] G. Merle; M. Wessling; K. Nijmeijer, J. Membr. Sci, 2011, 377, 1-35. [2] A. R. Katritzky; Z. Zakarial; E. Lunt; P. G. Jones; O. Kennard, J. Chem. Soc., Chem. Commun., 1979, 6, 268-269.

(Invited) Effect of Water and Carbon Dioxide on Anion-Exchange Membrane Fuel Cells

A decade of intensive research work on Anion Exchange Membrane Fuel Cells (AEMFCs) has finally yielded a high cell performance that is suitable for automotive applications. This achievement is mainly a result of the successful development of new anion-exchange membranes (AEMs) with high hydroxide conductivity (100 mS cm-1 and above). Thanks to these high-performance membranes, AEMFCs with power densities higher than 1 W cm-2 and limiting current densities above 4 A cm-2 have been reached [1-2], which seemed far from possible only a couple of years ago. In spite of this remarkable progress on cell performance, it is the low performance stability during cell operation what hampers further development and implementation of AEMFCs. As it has been recently reviewed, most of the AEMFC performance stability data are still limited to <1000 h [3]. One of the key reasons in the reduction of cell performance is the presence of CO2. If pure oxygen is fed to the cathode, OH– alone is present and carries the charge. If ambient air is used instead of pure oxygen, carbonation processes occur in which OH– as a counteranion reacts with CO2 present in air to produce (bi)carbonates. The main result of this carbonation process is a significant decrease in the effective anion conductivity in the AEM and, in turn, a reduction of the AEMFC power output [4-5]. While the carbonation process seems to be reversible [6-7], and so it could be mitigated, it may affect the chemical stability of the membrane, and in turn the cell performance stability. Furthermore, the hydroxide anions transported from the cathode to the anode may attack the positively charged functional groups of the polymeric membrane (and ionomer), neutralizing part of it and suppressing its anion-conducting capability. This process may actually cause irreversible performance losses during cell operation. To address this challenge, several new stable ionomeric materials have been proposed, and while they perform well in ex-situ chemical stability studies, their performance is still limited in real operating fuel cells. Although cation chemistry dictates the intrinsic chemical stability of the anion-conducting ionomeric materials, it was recently shown that the hydration level at which the fuel cell operates significantly affects the chemical degradation [8-9]. This relationship between local cell hydration and ionomeric material degradation has been analyzed in modelling studies, providing further insights about the critical role of water on the performance stability [10]. This talk will discuss the relationship between water, CO2, membrane/ionomer degradation, and their impact on the AEMFC performance stability. A unique recently developed model capable of predicting the performance stability of AEMFCs will be also presented. By using membranes with achievable targeted properties, the model predicts an AEMFC life-time higher than 8000 h [10], suitable for automotive applications. [1] T. J. Omasta, X. Peng, H. A. Miller, F. Vizza, L. Wang, J. R. Varcoe, D. R. Dekel, and W. E. Mustain; J. Electrochem. Soc. 165(15), J3039-J3044, 2018. [2] L. Q. Wang, E. Magliocca, E. L. Cunningham, W. E. Mustain, S. D. Poynton, R. Escudero-Cid, M. M. Nasef, J. Ponce-Gonzalez, R. Bance-Souahli, R. C. T. Slade, D. K. Whelligan, and J. R. Varcoe; Green Chem. 19, 831-843, 2017. [3] D. R. Dekel; J. Power Sources 375, 158-169, 2018. [4] N. Ziv, W. E. Mustain, and D. R. Dekel; ChemSusChem 11(7), 1136-1150, 2018. [5] U. Krewer, C. Weinzierl, N. Ziv, and D. R. Dekel; Electrochimica Acta 263, 433-446, 2018. [6] N. Ziv and D. R. Dekel; Electrochemistry Communications 88, 109-113, 2018 [7] S. Gottesfeld, D. R. Dekel, M. Page, C. Bae, Y. Yan, P. Zelenay, and Y.-S. Kim; J. Power Sources 375, 170-184, 2018. [8] C. E. Diesendruck and D. R. Dekel, Current Opinion in Electrochem. 9, 173–178, 2018. [9] D. R. Dekel, M. Amar, S. Willdorf, M. Kosa, S. Dhara, and C. Diesendruck; Chem. Mater. 29, 4425-4431, 2017. [10] D. R. Dekel, I. G. Rasin and S. Brandon; J. Power Sources, 420, 118-123, 2019.

Structure-Transport Relationships of Anion Exchange Membranes

Anion exchange membrane (AEM) fuel cells are emerging energy conversion technologies. A significant challenge in these devices lies in the core component, the AEM, which must possess high ionic conductivity to minimize Ohmic losses and exhibit chemical stability in highly basic conditions. A significant amount of effort has been expended to develop new anion exchange polymers with enhanced transport functionality. However, understanding of how anion transport in these polymers is related to hydration and nano-morphology is far from adequate. In this work, we report a systematic study on PAP-TP-85, an AEM with promising cell performance.1 A commercial AEM (Fuma FAA3) is used for comparison in this study. Membrane water uptake and anion conductivity in liquid and vapor as well as the impact of various anion forms on these properties are investigated. Small-angle X-ray scattering (SAXS) is used to probe hydrated AEM nanostructure, which is correlated to the membrane uptake and transport properties. Our results show that these AEMs lack a phase-separated nanostructure, regardless of their counter-anion form and hydration level. This is associated with their weak electrolytes behavior, which also explains their lower ion conductivity values (compared to proton exchange membranes), despite having higher water content and greater ion exchange capacity (IEC). Water content plays a more significant role than the temperature in controlling the anion conductivity of these weak electrolytes in water vapor. Comparing the water content in liquid vs. saturated vapor, both AEMs show Schroeder’s paradox regardless of counter-anion form. This study also demonstrates the importance of hydration level and ion concentration for anion transport in amorphous AEMs and provides further understanding into their parameters governing their structure-transport relationship and sheds light into designing AEMs with improved performance. Wang, J.; Zhao, Y.; Setzler, B. P.; Rojas-Carbonell, S.; Ben Yehuda, C.; Amel, A.; Page, M.; Wang, L.; Hu, K.; Shi, L.; Gottesfeld, S.; Xu, B.; Yan, Y., Poly(aryl piperidinium) membranes and ionomers for hydroxide exchange membrane fuel cells. Nature Energy 2019.

Synthesis of Poly(norbornene) Anion Conducting Membranes for Alkaline Electrochemical Devices: Structure-Property Relationships

Anion-exchange membranes (AEMs) are used in electrochemical energy storage and conversion devices such as batteries, fuel cells, and electrolyzers. The development of AEMs with long-term alkaline stability and high anion conductivity (i.e. hydroxide, carbonate and bicarbonate) is of current interest. The benefits over proton-exchange membrane (PEM) devices include the use of non-precious catalysts, facile reaction kinetics, and reduced fuel crossover. However, the issues with the low ionic conductivity, poor stability at high pH, and high water uptake are need to be addressed. A series of homopolymers and block copolymers containing non-hydrolysable backbone and long-chain head-group tethers based on vinyl addition and ring-opening metathesis polymerization (ROMP) of norbornenes were synthesized for use in AEM fuel cells. The focus of this talk is on the structure-property relationships of poly(norbornene) anion exchange membranes. Polymers were cross-linked with N,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHDA) to control the water uptake, and improve the mechanical properties. The structure property relationship of AEMs towards high ionic conductivity was correlated with ion-exchange capacity (IECs), number and size of the blocks, molecular weight, and polydispersity. The membranes had record high conductivity of 212 mS/cm at 80 °C and low water uptake. The long-term alkaline stability showed <1% conductivity loss in over 1200 h at 80 °C. The membranes have been used in anion-exchange membranes fuel cells and electrolyzers.

Preparation of Bacterial Cellulose Based Polymer Anion Exchange Membrane and Application for Fuel Cell

Nowadays, due to the excellent situation of fuel cell with high energy conversion rate and environmental protection, domestic research on fuel cell is endless. Electrolytes, as an important part of it, are extremely important. However, the ordinary electrolyte is liquid, which causes a lot of trouble and is especially inconvenient to carry. Therefore, liquid electrolyte is replaced by solid electrolyte in this paper. In addition, because bacterial cellulose (BC) membrane has many characteristics such as ultra-fine mesh structure, high mechanical strength, low cost and nice degradability, etc., which was used as the matrix scaffold in this paper and was doped with quaternary ammonium salt (QA) of PDDA to prepare a new anion exchange membrane called BC-PDDA. Furthermore, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal analysis (TG), ion exchange capacity (IEC) and mechanical properties of BC-PDDA membrane were depicted in detail to explore their applicability in fuel cells. It was found that BC-PDDA membrane has strong mechanical properties and high anionic conductivity (OH-) , which reaches 0.051 S cm-1, and has broad application potential in fuel cells.

High Anionic Conductive Form of PbxSn2–xF4

A high anionic conductivity of ∼3.5 × 10–3 S cm–1 at room temperature is achieved for PbxSn2–xF4 (x = 1.21) obtained by annealing a mechanically milled PbF2/SnF2 mixture at 400 °C. The observed syn...

High-performing rechargeable/flexible zinc-air batteries by coordinated hierarchical Bi-metallic electrocatalyst and heterostructure anion exchange membrane

Due to the lack of highly efficient and low-cost oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst and alkaline anion exchange membrane (AEM), advanced rechargeable zinc-air batteries are largely hindered in many applications from wearable electronics to electric vehicles. Herein, a hybrid of porous Co3O4 anchoring on MnO2, then interpenetrating with CNTs (Co3O4/MnO2-CNTs) is synthesized via facile hydrothermal process, and an AEM (CS/EMImC-Co-EP/GO) employing semi-interpenetrating network structure is fabricated with a simple solution-casting method. The porous nanoparticles and chrysalis-like hybrid as well as strong bi-metallic coupling effect build highways and buffer zones for reactant and electrons transfer for ORR/OER. In addition, due to the competition of bottom Co atoms, the density functional theory (DFT) proves that the neighbor Mn sites (Mn1 and Mn2) of the MnO2(110) surface are evidently activated, which prompts the catalytic activity of hybrids by making the Mn1, Mn2 3d density of states move forward lower energy entirely. As a result, Co3O4/MnO2-CNTs exhibit superior ORR/OER activities with the low potential difference (ΔE) of 0.85 V and impressive performances in rechargeable aqueous zinc-air batteries (power density: 534 mW cm−2). Moreover, combining AEM integrated into rechargeable flexible all-solid-state zinc-air batteries and stack, the enhancement natures of wearable devices are achieved even under different bending angles benefiting from high hydroxyl anion conductivity and remarkable flexibility of AEM semi-interpenetrating network, which accelerates ion transport by the synergy of hopping and vehicle mechanisms. Furthermore, the flexible all-solid-state zinc-air batteries show excellent tolerance toxicity of CO2.

A K+/Na+ co-binding state: Simultaneous versus competitive binding of K+ and Na+ to glutamate transporters

Plasma membrane-associated glutamate transporters play a key role in signaling by the major excitatory neurotransmitter glutamate. Uphill glutamate uptake into cells is energetically driven by coupling to co-transport of three Na+ ions. In exchange, one K+ ion is counter-transported. Currently accepted transport mechanisms assume that Na+ and K+ effects are exclusive, resulting from competition of these cations at the binding level. Here, we used electrophysiological analysis to test the effects of K+ and Na+ on neuronal glutamate transporter excitatory amino acid carrier 1 (EAAC1; the rat homologue of human excitatory amino acid transporter 3 (EAAT3)). Unexpectedly, extracellular K+ application to EAAC1 induced anion current, but only in the presence of Na+ This result could be explained with a K+/Na+ co-binding state in which the two cations simultaneously bind to the transporter. We obtained further evidence for this co-binding state, and its anion conductance, by analyzing transient currents when Na+ was exchanged for K+ and effects of the [K+]/[Na+] ratio on glutamate affinity. Interestingly, we observed the K+/Na+ co-binding state not only in EAAC1 but also in the subtypes EAAT1 and -2, which, unlike EAAC1, conducted anions in response to K+ only. We incorporated these experimental findings in a revised transport mechanism, including the K+/Na+ co-binding state and the ability of K+ to activate anion current. Overall, these results suggest that differentiation between Na+ and K+ does not occur at the binding level but is conferred by coupling of cation binding to conformational changes. These findings have implications also for other exchangers.

Flame-retardant AEMs based on organic-inorganic composite polybenzimidazole membranes with enhanced hydroxide conductivity

Efficient anionic conductivity accompanied with flam-resistance is of great importance for solid electrolyte. Herein, anion exchange membranes (AEMs) based on polybenzimidazole (PBI) and 1-butyl-3-methyl imidazolium phosphotungstate (PWA-IL) have been prepared. The obtained PWA-IL can be dispersed in PBI matrix uniformly aiming to enhance the anion conductivity. Especially, it is found that PWA-IL endows the composite membranes with flame-resistance features. Such a phenomenon may be rooted from the nature of non-flammable of 1- butyl-3-methylimidazolium bis (trifluoromethylsulfony)imide (IL) and phosphotungstic acid (PWA), which constitute the organic-inorganic filler PWA-IL. Simultaneously, the anionic conductivity of the obtained composite membranes improved from 48.9 mS cm−1 to 75.8 mS cm−1 under fully hydrated conditions at 80 °C. Enlarged elongation and small decline in tensile strength was observed due to the plasticization from 1-butyl-3-methyl imidazolium phosphotungstate. Polybenzimidazole backbones provide tough mechanical properties (strength more than 60 MPa and elongation more than 6%) and good thermal stability, which meet the need of wide applications.

Discovering the chloride pathway in the CFTR channel

Cystic fibrosis (CF), a lethal monogenic disease, is caused by pathogenic variants of the CFTR chloride channel. The majority of CF mutations affect protein folding and stability leading overall to diminished apical anion conductance of epithelial cells. The recently published cryo-EM structures of full-length human and zebrafish CFTR provide a good model to gain insight into structure–function relationships of CFTR variants. Although, some of the structures were determined in the phosphorylated and ATP-bound active state, none of the static structures showed an open pathway for chloride permeation. Therefore, we performed molecular dynamics simulations to generate a conformational ensemble of the protein and used channel detecting algorithms to identify conformations with an opened channel. Our simulations indicate a main intracellular entry at TM4/6, a secondary pore at TM10/12, and a bottleneck region involving numerous amino acids from TM1, TM6, and TM12 in accordance with experiments. Since chloride ions entered the pathway in our equilibrium simulations, but did not traverse the bottleneck region, we performed metadynamics simulations, which revealed two possible exits. One of the chloride ions exits includes hydrophobic lipid tails that may explain the lipid-dependency of CFTR function. In summary, our in silico study provides a detailed description of a potential chloride channel pathway based on a recent cryo-EM structure and may help to understand the gating of the CFTR chloride channel, thus contributing to novel strategies to rescue dysfunctional mutants.

A mechanically robust multication double-network polymer as an anion-exchange membrane: High ion conductivity and excellent chemical stability

Three membranes containing different cations with various levels of basicity were prepared for anion exchange application. All membranes show high anion conductivity at 80 °C (in the range of 83–117 mS cm−1). Beside OH− conductivity, the chemical stability and mechanical properties of membranes were tuned by changing the degree of crosslinking. As the best-optimized membrane, the Q-Poly 3 exhibit an OH− conductivity equal to 103 mS cm−1, max power density equal to 89 mW cm−2 and fuel crossover less than 10% of Nafion. Crosslinking in Q-Poly 3 cause superior mechanical properties (tensile strain equal to 40.39% and tensile strength equal to 51.25 MPa). This membrane also shows good mechanical properties after long time performance. The porous morphology of this membrane leads to the water uptake value of 91% (at room temperature), but it exhibits a relatively low swelling ratio (18%) due to the presence of crosslinking. After 14 days, Q-Poly 3 display very good chemical alkaline stability, and its anion conductivity reduce less than 7%.

Schiff base functionalized chitosan anion exchange membranes with 1,4-dichlorobutane as the crosslinker

A series of composite membranes (CS-PY-DLx) were synthesized by using schiff base functionalized chitosan (CS-PY) as the polymer matrix, 1,4-dichlorobutane (DL) as the crosslinker, the quaternization reagent is iodomethane. In this work, pyridine groups grafted on chitosan were converted into quaternary ammonium salt while forming cross-linked network structure. The FT-IR shows that the CS-PY-DLx membranes has been successfully prepared. The introduction of cross-linked structure enhances the alkali resistance, thermal stability and other properties of CS-PY-DLx membranes. When the cross-linked degree is 25%, the anion exchange membrane had the maximum tensile strength (24.45 MPa), and the anionic conductivity reaches 7.08 × 10−3 S cm−1 at 70 °C. The alkali resistance test was researched under the condition of 3 mol L−1 KOH solution for 120 h at 80 °C, which showed that the OH− conductivity of CS-PY-DL25 membranes retains approximately 79.7% of its initial conductivity, revealing the excellent alkali resistance. Methanol permeability was only 0.37–0.72% of the Nafion-117 membrane in 3M methanol at 60 °C, indicating an excellent resistance to alcohol.

Characterization of Leachates from Landfills Containing MSW-I Residues

The objective of this study was to characterize the leachate collected from landfills containing municipal solid waste incineration (MSW-I) ashes in the range of 20%–100% by weight. Results suggested that the conductivity and concentrations of major cations (Na+,K+,Ca2+) and anions (Cl− and Br−) increased with ash content, while alkalinity decreased with ash content. MSW-I ash contents had little effect on pH, TOC, NH4+, trace metals, and SO42−. Comparing the metal composition in the MSW-I ashes and associated ash monofill leachate, the leaching of metals, including Mg, Fe, Cu, Ni, and Al, were not as significant as expected. As, Cd, Pb, and Zn in ash monofill leachate were even below the quantification limit. The effect of MSW-I ash on landfill systems is further discussed. Leachate containing the MSW-I ash might increase the risk of leachate collection system (LCS) clogging. The risk of mineral precipitation in the LCS increased with the ash content mainly due to the increasing concentration of Ca. High ionic strength as well as the high anion ratio of the leachates might increase the hydraulic conductivity of geosynthetic clay liners (GCLs).

Injection of mRNA isolated from trophozoites of Giardia intestinalis induces expression of three types of chloride currents in Xenopus laevis oocytes.

Giardia lamblia is one of the most important worldwide causes of intestinal infections, yet little is known about its cellular physiology, especially the diversity of ionic channels that this parasite expresses. In this work, we show that injection of mRNA isolated from trophozoites of Giardia, into Xenopus laevis oocytes, induces expression of three types of chloride currents (here referred to as ICl‐G1, ICl‐G2, and ICl‐G3), which have different biophysical and pharmacological properties. ICl‐G1 currents show inward rectification and voltage dependence are enhanced by hypotonicity, show a selectivity sequence of (I > Br > Cl > F), and are inhibited by NPPB, DIDS, SITS, 9AC, DPC, and Zinc. These findings suggest that ICl‐G1 is the result of expression of chloride channels related to ClC2. ICl‐G2 currents show outward rectification and are dependent of intracellular calcium, its selectivity sequence is (Cl > Br > I > F) and are inhibited by NPPB, DIDS, SITS, 9AC, DPC, niflumic acid, tannic acid, and benzbromarone. These findings suggest that they are produced by calcium dependent chloride channels (CaCC). The third type of currents (ICl‐G3) appears only after a hypoosmotic challenge, and has similar properties to those described for ICl‐swell, such as outward rectification, instant activation, and slow inactivation at large depolarizing voltages. They were blocked by NPPB, DIDS, 9AC, NIf, DCPIB, and tamoxifen. Our results indicate that Giardia intestinalis has at least three types of anion conductances.

Synthesis of anion conducting polymer electrolyte membranes by Pd-Catalyzed Buchwald-Hartwig Amination coupling reaction

A novel aryl bromine bearing polymer was synthesized by Friedel-Crafts polycondensation. This precursor polymer substrate was used for C–N coupling via Buchwald-Hartwig amination to incorporate 9 examples of aryl amines into the polymer chains with high conversions (80–100%). Two aminated polymers were subsequently quaternized to give anion conducting polymers. These quaternary ammonium polymers show promising electrochemical membrane property because of their ability to transport mobile anions through the material while being electrically insulating. Membrane characteristics crucial to high electrochemical performance including ion exchange capacity, anion conductivity, water uptake, swelling ratio, and alkaline stability were evaluated.

Empirical Electronic Polarizabilities: Deviations from the Additivity Rule. II. Structures Exhibiting Ion Conductivity

AbstractIon conductivity in minerals and compounds is associated with continuous migration paths and leads to negative total electronic polarizability deviations [Δ = (αobs−αcalc)/αobs)] up to 13%. Such deviations can be related to continuous migration paths determined in an earlier Voronoi–Dirichlet Partition (VDP) analysis of fast‐ion conductors, that is, compounds such as LiB3O5 with 1D conductivity, Li4SiO4 with 2D conductivity, and Li2SO4 with 3D conductivity. Using the Voronoi–Dirichlet (VD) method in this study, the migration paths and the dimensionality of many more compounds with negative polarizability deviations are identified. Continuous migration paths are found for the confirmed Li‐ion conductors LiFePO4 and Li3VO4 and for the potential Li‐ion conductors LiGeBO4, CsLiB6O10, Li2Ti3O7, LiMn0.8Fe0.17PO4, Li2NaPO4, and LiNaSO4. Similarly, continuous migration paths are found for the confirmed Na‐ion conductors Na4P2O7, Na2SO4, and Na6Mg(SO4)4, and for the potential Na‐ion conductors Na6Mg2(CO3)4SO4, Na2TiSiO5, NaPO3, Na3SO4F, Na6(SO4)2FCl, Na15(SO4)5F4Cl, Na21(SO4)7F6Cl, Na22K(CO3)2(SO4)9Cl, and Na2SeO4. Potassium migration paths are found for the confirmed ion conductors KVO3 and K2SO4. In contrast to the application of VD partitioning of cation conductors, VD partitioning of anion conductors leads to migration paths in (Zr,Y)O8 polyhedra in Zr0.894Y0.095Hf0.011O1.95 and (Gd,Hf)O6 and (Gd,Hf)O8 polyhedra in Gd2Hf2O7 where O2− ions are mobile.

Preparation of Polysulfone anion exchange membranes incorporated with Gemini cationic molecules

A series of anion exchange membranes were synthesized based on polysulfone incorporated with Gemini cationic surfactant as conductivity improving additives. The effect of addition of diethyl maleate bis[(dodecyldimethyl)chloride/ammonium bromide] (G12–2-12) cationic surfactant with different content on the water uptake, swelling ratio, ion exchange capacity, mechanical property, conductivity, and alkaline stability of the membranes were all investigated and the aforementioned membranes were also characterized by FT-IR, TGA and SEM. The result revealed that water uptake, swelling ratio, ion exchange capacity, conductivity were increased with the increasing of G12–2-12 content. The optimum P-X (X ≠ 0) membrane (WG12–2-12% = 40) showed an IEC of 1.20 meq g−1 with water uptake of 20.33% and hydroxide conductivity of 9.53 10−3 S cm−1 obtained at 80 °C. Interestingly, these membranes displays outstanding thermal stability with stable up to 150 °C, good mechanical strength with tensile stress in the range of 40.75 MPa–25.16 MPa and excellent chemical stabilities of up to 120 h in 6 M KOH without obvious loss of anionic conductivity (≤5.0%).

Comb-shaped anion exchange membrane with densely grafted short chains or loosely grafted long chains?

Anion exchange membranes (AEMs) are crucial components for advanced energy and environment processes including alkaline fuel cells, redox flow batteries, and industrial effluent treatment; while low anionic conductivity and poor stability remain the major challenges for the widespread implementation of AEMs. Through molecular engineering, comb-shaped AEMs have been proved possessing the capability of delivering both high conductivity and good alkaline stability. However, how to precisely control the side chain topology and how the chain topology would influence the membrane properties need to be further elucidated. We hereby propose a radically novel and readily scalable route towards the controllable synthesis of comb-shaped AMEs and we were able to determine the length of side chains and the number of ionic groups along the side chains. To probe the effect of side chain topology on membrane properties, two types of AEMs of densely grafted short side chains or loosely grafted long side chains with similar ion exchange capacity (IEC, ∼1.7 mmol/g) were synthesized and compared. We found that the comb-shaped AEMs with loosely grafted long chains (LG-LS-DIm), with higher hydroxide conductivity (55 mS cm−1 at 30 °C) and better alkaline stability (∼80 % of IEC retention after soaking in 2 mol L−1 NaOH solution at 60 °C for 25 days), outperform those with densely grafted short chains (HG-SS-DIm) and the benchmark main-chain type AEMs (DIm-PPO), which is also superior to those of conventional linear AEMs with densely functionalized structure.

Super-Strong Nafion/PVA/Uhmwpe Membranes for Proton and Hydroxide Ion-Exchange Fuel Cells

Perfluorosulfonic acid (PFSA) ionomers have been used extensively in proton exchange membranes due to their high proton conductivity and strong electrochemical stability. However, proton and anion conductivity through the PFSA membranes are contingent upon water uptake, but high water content in the membrane causes loss of long-term durability of the fuel cell system because of the water swelling-induced reduction in membrane’s mechanical strengths. Large body of literatures are available to address these issues, for example, hydroscopic nanoparticulate fillers have been used for self-hydration of the membrane, and aligned polytetrafluoroethylene (PTFE) has been employed to reinforce the tensile strengths of the PFSA ionomer. Unfortunately, there is yet no report to date that can resolve pareto fronts issues, i.e., simultaneously having high proton conductivity and high tensile property. Besides, the cost of PFSA membranes, e.g., Nafion, is still prohibitively high. Here, we report a new and low-cost hierarchical membrane with high proton/anion conductivity, low moisture/methanol uptake and super-high tensile strengths. The new membrane is a hybridized composite structure consisting of biaxially oriented nanoporous ultrahigh molecular weight polyethylene (UHMWPE) film coated with Nafion and polyvinyl alcohol (PVA) blend. The tensile strength of the composite membrane is at least 10 times higher than that of the pure Nafion membrane when fully humidified, and the proton and alkaline conductivity is comparable to that of the Nafion/PVA blend. The nanoporous UHMWPE simultaneously acted to provide the high tensile strengths, ion-conductivity selectivity and nanoconfinement to limit the water and methanol uptake. Thus the new hierarchical Nafion/PVA/UHMWPE membrane is potentially an ideal ion-exchange membrane for low temperature hydrogen and direct methanol fuel cells. The work is financially supported by the theme-based research project of the university grants committee of Hong Kong, Grant No. T23-601/17-R

Design of Mechanically Robust Polymer Membranes for Non-Aqueous Flow Battery

Large scale grid storage is imperative for an efficient use of renewable energies. While aqueous redox flow batteries (RFBs) such as a vanadium-based aqueous RFB are relatively mature technologies for a grid storage, non-aqueous RFBs present an attractive alternative strategy for potentially providing much higher energy density. One of the key enablers for non-aqueous RFBs is mechanically robust and highly ion-conductive membranes. In aqueous RFBs, membranes can achieve high proton or anion conductivity due to water mediating their ion conduction, thus there are various high performance membranes for aqueous RFBs. On the other hand, for membranes in non-aqueous RFBs, achieving high ion conductivity while maintaining mechanical and chemical stability is a major challenge. The design principle for such membranes is poorly understood due to the complexity of the system. Our membranes are developed for a non-aqueous RFB with an alkali alloy anode technology that has the potential to achieve high energy density, high safety, low cost and long cycle life. This presentation will discuss the fundamental design principle in polymer membranes for non-aqueous RFBs and our recent efforts on the development of novel plasticized polymer membranes that simultaneously provide high conductivity and tailored mechanical modulus. In this study, mechanically robust crosslinked poly(ethylene oxide) membranes were synthesized and doped with sodium triflate and tetraglyme. The relationships between ion conductivity (reached up to 10-4-10-3 S/cm at r.t.), salt/gel content, glass transition temperature (Tg) and mechanical properties are investigated. The synthesized membranes are mechanically robust with storage modulus maintaining at ~1 MPa from -20 °C to 180 °C even saturated with tetraglyme. Furthermore, mechanically tailored novel single-ion conducting polymer electrolytes (SICPEs); block and graft copolymers of poly[(4-styrenesulfonyl) (trifluromethane-sulfonyl)imide] (poly(STF)) and poly[1-[3-(methacryloyloxy)-propylsulfonyl]-1-(trifluoromethanesulfonyl)imide] (poly(MPA)), were investigated. The SICPEs were synthesized by covalently attaching anionic moieties to the polymer backbones that only allows specific cations, such as lithium or sodium ions, to move freely and provide ionic conductivity (i.e. the transference number is close to 1) which is imperative for RFBs. These novel SCPE membranes include a membrane with a flexible polymer backbone to afford mechanical robustness and stretchability, and poly(STF) or poly(MPA) as side chains to provide single-ion conductivity. The effect of monomer type, degree of polymerization of the side chain, and different cations are also studied. The obtained polymer membrane showed 100% elongation and around 10-4 S/cm single-ion conductivity (no salt) at 30 °C after being doped with propylene carbonate. This work is funded by Dr. Imre Gyuk, Office of Electricity Delivery and Reliability, Department of Energy and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC.