Anion Conductance Research Articles

The Role of EAAT4 in Epidermal Differentiation and Calcium Homeostasis During Aging

The Role of EAAT4 in Epidermal Differentiation and Calcium Homeostasis During Aging

Microstructural orientation of anion exchange membrane through mechanical stretching for improved ion transport

Synthesis of anion exchange membranes (AEMs) with orientated nano/micro-structure and with tunable ion-channels is of great interest for applications in fuel cells, water electrolyzers, and redox flow batteries. However, there is still a dearth of work in the detailed understanding of anion conductivity from a polymer structure‒property perspective. Herein, we demonstrate an easy and versatile strategy to fabricate highly conductive AEMs. By stretching the AEMs, an improvement in OH− conductivities of AEMs is achieved. The effect of elongation at different water contents on polymer structures and OH− conductivities was investigated by a combination of molecular dynamics (MD) simulation and experimental study, giving insights into macromolecular orientation at the atomic level. The morphological changes, which consist of oriented polymer chains and elongated water clusters, are quantified by a combination of two dimensional small angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and radial distribution functions. Detailed analyses of interatomic distances reveal morphological variations of hydrophilic domains and their interactions with water and OH− under elongation at different hydration levels. Furthermore, the OH− conductivities of our synthesized quaternized poly(2,6-dimethyl-1,4-phenylene oxide) (QPPO) AEMs increased significantly after stretching to 20% elongation at all water contents. Specifically, OH− conductivity of stretched QPPO was 2.24 times more than the original AEM at 60% RH. The higher relative increase in OH− conductivity at lower water content may be caused by the lower flexibility of side chains at lower hydrated level. This work verifies the significance of porous and/or oriented AEM structure in the improvement on anion conductivity and water transport efficiency.

Recent Advancements of Polymeric Membranes in Anion Exchange Membrane Water Electrolyzer (AEMWE): A Critical Review.

Water electrolysis coupled with renewable energy is one of the principal methods for producing green hydrogen (or renewable hydrogen). Among the different electrolysis technologies, the evolving anion exchange membrane water electrolysis (AEMWE) shows the utmost promise for the manufacture of green hydrogen in an inexpensive way. In the present review, we highlight the most current and noteworthy achievements of AEMWE, which include the advancements in increasing the polymer anionic conductivity, understanding the mechanism of degradation of AEM, and the design of the electrocatalyst. The important issues affecting the AEMWE behaviour are highlighted, and future constraints and openings are also discussed. Furthermore, this review provides strategies for producing dynamic and robust AEMWE electrocatalysts.

Hydrodynamic interactions in ion transport-Theory and simulation.

We present a hydrodynamic theory describing pair diffusion in systems with periodic boundary conditions, thereby generalizing earlier work on self-diffusion [B. Dünweg and K. Kremer, J. Chem. Phys. 99, 6983-6997 (1993) and I.-C. Yeh and G. Hummer, J. Phys. Chem. B 108, 15873-15879 (2004)]. Its predictions are compared with Molecular Dynamics simulations for a liquid carbonate electrolyte and two ionic liquids, for which we characterize the correlated motion between distinct ions. Overall, we observe good agreement between theory and simulation data, highlighting that hydrodynamic interactions universally dictate ion correlations. However, when summing over all ion pairs in the system to obtain the cross-contributions to the total cationic or anionic conductivity, the hydrodynamic interactions between ions with like and unlike charges largely cancel. Consequently, significant conductivity contributions only arise from deviations from a hydrodynamic flow field of an ideal fluid, which is from the local electrolyte structure as well as the relaxation processes in the subdiffusive regime. In the case of ionic liquids, the momentum-conservation constraint additionally is vital, which we study by employing different ionic masses in the simulations. Our formalism will likely also be helpful to estimate finite-size effects of the conductivity or of Maxwell-Stefan diffusivities in simulations.

Mutation in glutamate transporter homologue GltTk provides insights into pathologic mechanism of episodic ataxia 6

Episodic ataxias (EAs) are rare neurological conditions affecting the nervous system and typically leading to motor impairment. EA6 is linked to the mutation of a highly conserved proline into an arginine in the glutamate transporter EAAT1. In vitro studies showed that this mutation leads to a reduction in the substrates transport and an increase in the anion conductance. It was hypothesised that the structural basis of these opposed functional effects might be the straightening of transmembrane helix 5, which is kinked in the wild-type protein. In this study, we present the functional and structural implications of the mutation P208R in the archaeal homologue of glutamate transporters GltTk. We show that also in GltTk the P208R mutation leads to reduced aspartate transport activity and increased anion conductance, however a cryo-EM structure reveals that the kink is preserved. The arginine side chain of the mutant points towards the lipidic environment, where it may engage in interactions with the phospholipids, thereby potentially interfering with the transport cycle and contributing to stabilisation of an anion conducting state.

Investigation of Fumasep® FAA3-50 Membranes in Alkaline Direct Methanol Fuel Cells.

This paper describes the use of a commercial Fumasep® FAA3-50 membrane as an anion exchange membrane (AEM) in alkaline direct methanol fuel cells (ADMFCs). The membrane, supplied in bromide form, is first exchanged in chloride and successively in the hydroxide form. Anionic conductivity measurements are carried out in both a KOH aqueous solution and in a KOH/methanol mixture. AEM-DMFC tests are performed by feeding 1 M methanol, with or without 1 M KOH as a supporting electrolyte. A maximum power density of 5.2 mW cm-2 at 60 °C and 33.2 mW cm-2 at 80 °C is reached in KOH-free feeding and in the alkaline mixture, respectively. These values are in good agreement with some results in the literature obtained with similar experimental conditions but with different anion exchange membranes (AEMs). Finally, methanol crossover is investigated and corresponds to a maximum value of 1.45 × 10-8 mol s-1 cm-2 at 50 °C in a 1 M KOH methanol solution, thus indicating that the Fumasep® FAA3-50 membrane in OH form is a good candidate for ADMFC application.

Lipoic Acid-Assisted In Situ Integration of Ultrathin Solid-State Electrolytes

Ultrathin solid-state electrolytes (SSEs) have contributed to high-energy-density lithium-ion batteries (LIBs). However, when reducing thickness of SSEs, mechanical properties will inevitably deteriorate, even increasing the safety hazards. In this work, we developed an in-situ integration strategy to form an ultrathin SSE by combining a lipoic acid-assisted semi-interpenetrating polymer network and an ultrathin porous membrane. With this strategy, the thickness of the obtained SSE (named LA-SSE) is only 10 μm, and the LA-SSE possesses extraordinary mechanical performances to suppress the growth of lithium dendrites. Meanwhile, the flexible LA-SSE presents anionic conductivity of 0.036 mS cm–1 and promotes interfacial compatibility between the lithium anode and the electrolyte. By employing LA-SSE as the electrolyte, the assembled Li∥LA-SSE∥Li symmetric cell operated with long-term cycling (more than 3000 h), and the LiFePO4∥LA-SSE∥Li full battery worked steadily over 200 cycles at 0.5 C with a capacity retention of 84% at room temperature. This work provides a promising strategy for designing ultrathin SSEs, with satisfactory mechanical properties, excellent interfacial compatibility, and safety, for LIBs.

Metal-to-Insulating Transition in the Perovskite System YSr2Cu2FeO8-δ (0 < δ < 1) Modeled by DFT Methods.

Progress in the design of functional perovskite oxides relies on advances in density functional theory (DFT) methods to efficiently and effectively model complex systems composed of several transition-metal ions. This work reports the application of DFT methods to investigate the electronic structure of the YSr2Cu2FeO8-δ (0 < δ < 1) family in which the insulating, metal, or superconducting behaviors and even anion conductivity can be tuned by modifying the oxygen content. In particular, we assess the performance of the generalized gradient approximation (GGA), its Hubbard-U correction (GGA + U), and the strongly constrained and appropriately normed (SCAN) to model the metallic (idealized YSr2Cu2FeO8) and insulating (idealized YSr2Cu2FeO7) phases of the system. The analysis of the DFT results is supported by DC resistivity measurements that denote the metal character of the synthesized YSr2Cu2FeO7.86 and the semiconducting character of YSr2Cu2FeO7.08 prepared under reducing conditions. In addition, the band gap of YSr2Cu2FeO7.08, in the range of 0.73-1.2 eV, has been extracted from diffuse reflectance spectroscopy (DRS). While the three methodologies (GGA, GGA + U, SCAN) permit the reproduction of the crystal structures of the synthetized oxides (determined here in the case of YSr2Cu2FeO7.08 by neutron powder diffraction (NPD)), the SCAN emerges as the only one capable to predict the basic electronic and magnetic properties across the YSr2Cu2FeO8-δ (0 < δ < 1) series. The picture that emerges for the metal (δ = 0) to insulating (δ = 1) transition is the one in which oxygen vacancies contribute electrons to the filling of the Cu/Fe-3dx2-y2 states of the conduction band. These results validate the SCAN functional for future DFT investigations of complex functional oxides that combine several transition metals.

The Mechanism of Channel Opening of Anion Channelrhodopsin GtACR1: A Molecular Dynamics Simulation

Guillardia theta anion channelrhodopsin 1 (GtACR1) is a widely used inhibitor of optogenetics with unique conductance mechanisms and photochemistry. However, the molecular mechanism of light-gated anion conduction is poorly understood without a crystal structure for the intermediate state. In this study, we built the dark-state model based on the crystal structure of retinal and isomerized the model by twisting the C12-C13=C14-C15 dihedral step by step using molecular dynamics simulation. The conformational changes revealed the all-trans to 13-cis photoisomerization of the retinal chromophore cannot open the channel. There is no water influx, and a pre-opened K-like intermediate after photoisomerization of retinal is formed. During the opening of the ion channel, proton transfer occurs between E68 and D234. Steered molecular dynamics (SMD) and umbrella sampling indicated that the E68 and D234 were the key residues for chloride-ion conducting. We propose a revised channel opening pathway model of GtACR1 after analyzing (de)protonation of E68 and D234. Reprotonation of D234 will result in two different early L intermediates, named L1-like and L1‘-like, which correspond to the L1 and L1‘ intermediates reported in a recent study. Simulation results showed that L1-like may convert by parallel paths into L1‘-like and L2-like states. This model provides conformational details for the intermediate as well.

An end‐to‐end artificial intelligence platform enables real‐time assessment of superionic conductors

AbstractSuperionic conductors (SCs) exhibiting low ion migration activation energy (Ea) are critical to the performance of electrochemical energy storage devices such as solid‐state batteries and fuel cells. However, it is challenging to obtain Ea experimentally and theoretically, and the artificial intelligence (AI) method is expected to bring a breakthrough in predicting Ea. Here, we proposed an AI platform (named AI‐IMAE) to predict the Ea of cation and anion conductors, including Li+, Na+, Ag+, Al3+, Mg2+, Zn2+, Cu(2)+, F−, and O2−, which is ~105 times faster than traditional methods. The proposed AI‐IMAE is based on crystal graph neural network models and achieves a holistic average absolute error of 0.19 eV, a median absolute error of 0.09 eV, and a Pearson coefficient of 0.92. Using AI‐IMAE, we rapidly discovered 316 promising SCs as solid‐state electrolytes and 129 SCs as cathode materials from 144,595 inorganic compounds. AI‐IMAE is expected to completely solve the challenge of time‐consuming Ea prediction and blaze a new trail for large‐scale studies of SCs with excellent performance. As more experimental and high‐precision theoretical data become available, AI‐IMAE can train custom models and transfer the existing models to new models through transfer learning to constantly meet more demands.

Deeping insight of Mg(CF3SO3)2 and comprehensive modified electrolyte with ionic liquid enabling high-performance magnesium batteries

Research and development of appropriate electrolytes have been deemed as the key for the commercial utilization of rechargeable magnesium batteries (RMBs) with high energy densities, especially for the storage systems containing high capacity cathode materials. In this study, the cost-competitive magnesium salt Mg(CF3SO3)2, which is structurally similar to Mg(TFSI)2, has been proved to possess stronger hydrophobic property, weaker reducibility and reactivity with Mg anodes by experimental comparison and calculation analysis, whereas limited self-generated oxidation resistance of the anion and inferior ionic conductivity in aprotic solvents restrain its practical application. Herein a small amount of PP14TFSI ionic liquid (IL) as multifunctional additive in Mg(CF3SO3)2-based electrolytes has been demonstrated comprehensive improvements in performance, including broadened electrochemical window, ameliorated ionic conductivity (∼6 mS cm−1), homogenization and optimization in interfacial flux and composition, and stable cycling reversibility with low polarization (0.11 V), etc. The IL tailored electrolytes also exhibit desirable compatibility with Mo6S8 (66.9 mAh g−1 after 100 cycles at 0.1 C) and Cu3Se2 (131.7 mAh g−1 after 100 cycles at 200 mAh g−1). Meanwhile, the nucleophilicity of CF3SO3- has been initially discussed on the basis of the cycling results of S@MC||Mg (sulfur@microporous carbon||Mg) and CuS||Mg full batteries. This work has deepened the understanding of Mg(CF3SO3)2 and IL in RMB electrolytes, and provided a new insight for the exploration of electrolyte systems based on simple magnesium salts.

High-Temperature Anomaly of the Anionic Conductivity in LaF3 Crystals

High-Temperature Anomaly of the Anionic Conductivity in LaF3 Crystals

Model-based insights into the decarbonation dynamics of anion-exchange membranes

We present a model-based analysis of the transport of anions in anion exchange membranes (AEMs) with the aim of understanding the decarbonation process and its dynamics. The dynamic simulation model covers the diffusive and migrative transport of water, carbonate anions, and hydroxide anions through an AEM. To the best of our knowledge, this is the first model studying decarbonation process in AEMs. The model is validated using decarbonation data from anion conductivity measurements of ten different AEM materials. Driven by migrative transport, strong concentration gradients develop inside the membranes. A parameter study reveals that the ion-exchange capacity and the applied current have the largest effect on the decarbonation dynamics. Further, high hydroxide diffusivities increase the decarbonation time constant, whereas high carbonate diffusivities decrease it. The results further indicate that high diffusivities of both carbonates and hydroxide result in slower membrane decarbonation. This work provides new insights into properties determining the carbonation and decarbonation of AEMs, which is critical for AEM-based electrochemical devices such as fuel cells and electrolysers.

Ether-free polymer based bipolar electrolyte membranes without an interlayer catalyst for water electrolysis with durability at a high current density

In this study, bipolar membranes (BPMs) were fabricated employing the sulfonated poly(fluorine biphenyl indole) based proton exchange membrane (PEM) and the poly(arylene piperidinium) based anion exchange membrane (AEM) for the production of green hydrogen by water electrolysis. As those polymers comprise similar aromatic backbone structures without ether groups, excellent chemical durability of the constituent membranes was expected for the long-term energy efficient operation in a wide pH range. Three BPMs with different ionic conductivity pairs between PEM and AEM were designed to explore its effect on water electrolysis performance. At the fixed anionic conductivity of AEM of 0.0370–0.0923 S cm−1 at 30–70 °C, the proton conductivity of PEMs was tuned as 0.0379–0.1196 S cm−1, 0.0909–0.1598 S cm−1, and 0.1104–0.1739 S cm−1 at 30–70 °C. BPMs were steadily operated at low voltages below 1.5 V in the wide current density range of 0–1500 mA cm−2. Among them, the water electrolytic cell assembled with BPM 80/20 showed the best water electrolysis performance, as the cell voltage of BPM 80/20, BPM 70/30, and BPM 60/40 was 0.75 V, 0.98 V, and 1.08 V, respectively, under the current density of 700 mA cm−2 at 70 °C. It was much lower than that of AEM, 2.24 V and PEM 80/20, 1.81 V even in the absence of interlayer catalyst. Also, the synthesized BPM 80/20 was not only thermally and mechanically stable up to 298 °C and 19.15 MPa (tensile strength), but also chemically stable in the concentrated acidic and basic environment, as its weight loss was less than 5.4 % and 4.62 % in 4 M H2SO4 and 4 M KOH solutions for 4 weeks, respectively.

Hierarchical Fe3O4@LDH-incorporated composite anion exchange membranes for fuel cells based on magnetic field orientation

The trade-off between ionic conductivity and mechanical properties is the key issue facing anion exchange membranes (AEMs) at present. Herein, a new strategy combing three-dimensional (3D) hierarchical nanoarchitecture and magnetic field orientation was proposed to prepare imidazolium-functionalized poly(2,6-dimethyl phenylene oxide) (ImPPO)-based composite AEMs with simultaneously improved ionic conductivity and mechanical strength. Magnetic Fe3O4@LDH microspheres using Fe3O4 as the core and two-dimensional lamellar anion conductor, layered double hydroxide (LDH), as the shell were prepared through a simple co-precipitation method. The as-prepared Fe3O4@LDH was then incorporated into ImPPO matrix and induced by an external magnetic field to fabricate Fe3O4@LDH-orientated composite AEMs. The hierarchical-structured Fe3O4@LDH can not only effectively avoid the stacking of LDH laminates and thus fully play the ion conduction ability of LDH, but also contribute to the formation of continuous OH− ion transport pathway in the composite system after magnetic field induction. The magnetic-field-oriented membrane with 1% Fe3O4@LDH doping exhibited ionic conductivity of 128.9 mS cm−1 at 80 °C, which was 43.1% higher than that of pure ImPPO. Moreover, the high dry strength (30.7 MPa) and satisfactory wet strength and flexibility of the composite membrane were also obtained. The assembled direct methanol fuel cell demonstrated a peak power density of 11.7 mW cm−2, and showed an OCV retention of as high as 94.7% after continuous operation for 100 h, indicating their great potential for fuel cell applications.

HIGH-TEMPERATURE ANOMALY OF THE ANIONIC CONDUCTIVITY IN LaF&lt;sub&gt;3&lt;/sub&gt; CRYSTALS

The anionic electrical conductivity σdc(T) of the superionic LaF3 conductor single crystal has been studied by impedance spectroscopy in a wide (312–1073 K) temperature range. Electrical measurements in a protective nitrogen atmosphere have been carried out. It is shown that the σdc values change from 1.5 × 10–5 to 7 × 10–2 S/cm (by a factor of ~5 × 103) in the investigated temperature range. A high-temperature anomaly of the σdc(T) dependence has been found at T0 ≈ 970 K, which is apparently indicative of the onset of a diffuse (Faraday) phase transition in the LaF3 tysonite structure.

A focused review on structures and ionic conduction mechanisms in inorganic solid-state proton and hydride anion conductors

This review provides a focused discussion on the structures and ionic conduction mechanisms of inorganic solid-state proton and hydride anion conductors.

Stability and Evolution of the Crystal Structure of TbBaCo2O6-δ During Thermal Oxygen Release/Uptake.

A-site ordered double perovskites with the general formula LnBaCo2O6-δ (where Ln is a lanthanide element) present electrical and electrocatalytic properties that make them attractive as possible ceramic electrode materials for solid oxide cells or alkaline electrolyzers. The properties are highly influenced by the anion vacancy concentration, which is strongly related to the Co-oxidation state, and their location in the structure. Awareness of the stable phases is essential to synthesize, evaluate, and optimize the properties of LnBaCo2O6-δ oxides at operating conditions in different applications. TbBaCo2O6-δ are representative oxides of these layered perovskite systems. The present article reports a study of TbBaCo2O6-δ by electron diffraction, high-resolution electron microscopy, and powder neutron diffraction experiments at different temperatures. The synthesis of TbBaCo2O6-δ in air and slow cooling to room temperature (RT) at 5 °C h-1 leads to samples formed by distinct phases with different oxygen contents and crystal structures. The 122 and 112 phases (with ap × 2ap × 2ap and ap × ap × 2ap unit cells, respectively, with ap being the lattice parameter of the simple cubic perovskite structure) are predominant in quasi-equilibrium prepared samples (cooled at RT at 1 °C h-1) or prepared in Ar flow and quenched to RT. The evolution of the crystal structure of TbBaCo2O6-δ during thermal oxygen release/uptaking consists of modulation from the 122 phase to the 112 phase (or vice versa during uptaking) by creation/occupation of anion vacancies within the TbO1-δ planes. Anion vacancies are not detected in the oxygen crystallographic position different from those located within the TbO1-δ planes even at the highest temperatures, supporting the 2D character of the high anion conduction of the LnBaCo2O6-δ oxides.

Aquivion-based anion exchange membranes: Synthesis optimization via dispersant agents and reaction time

Alkaline membrane water electrolysis fed by renewable energy is a promising technology to produce “green” hydrogen for a variety of applications. Thanks to their unique characteristics of chemical, thermal and electrochemical stability, perfluorinated polymers are proposed as an alternative to hydrocarbon-based anion exchange membranes (AEMs) for applications in water electrolysers. A simple two-step functionalization reaction to introduce quaternary ammonium groups onto Aquivion® perfuorinated backbone is reported using a low toxicity dispersant. The most appropriate dispersant (Novec 7500) and reaction parameters (5 °C for 2 hrs) are selected. The complete conversion of the precursors into a quaternary ammonium salt is confirmed by a solid-state NMR study. Physico-chemical properties, thermal behavior and anion conductivity of the formed AEM are investigated. The phase separation characteristics of this perfluorinated polymer allow to reach a membrane ion mobility (μeff) 1.99 10−4 cm2 V−1 s−1, one order of magnitude higher than the FAA3-50 commercial membrane, meaning an enhanced ion dissociation. A very limited degradation of functional groups is demonstrated after immersion in alkaline solution, with only 2 % of ion exchange capacity (IEC) reduction against 14 % of the FAA3-50 commercial membrane. An electrolysis current density of 0.9 A cm−2 at 2.2 V and 90 °C, is achieved showing very promising applications for green hydrogen production.

Fast ion transport in mechanochemically synthesized SnF2 based solid electrolyte, NH4Sn2F5

Recent reports on fluoride ion batteries (FIBs) show its promising credentials as suitable alternatives for Li-ion batteries suffering with issues like high cost, limited source, and safety. Unlike to the other alternative battery technologies such as Na, FIBs are in the early stage of progress. Development of solid electrolytes with fast fluoride ion transport is one of the major challenges in FIBs. NH4Sn2F5 belongs to the SnF2 based MSn2F5 (M: K, Rb, and NH4) solid electrolytes exhibiting two-dimensional F ion conduction. The present work reports the structural and transport details of mechanochemically synthesized NH4Sn2F5, where the material is prepared just by milling the initial SnF2 and NH4F powders (2:1) for 10 h without any heat treatment. The formation of the material exhibiting monoclinic structure at room temperature (RT) is confirmed by X-ray diffraction followed by the Rietveld refinement. The temperature dependent conductivity results at different temperature regions are explained with respect to its structural transformations, which is furthermore correlated with the differential scanning calorimetry observation. Later the conductivity values at different temperatures of mechanochemically prepared NH4Sn2F5 are compared with the earlier reported MSn2F5 (M: Na and K) materials synthesized by the same method and the results are explained with respective to their crystal structure. The current study shows that the presence of the larger NH4 cation in MSn2F5 (M: Na, K, NH4) systems causes fast transport of F ions resulting in the highest fluoride ionic (anionic) conductivity value. Like BaSnF4, the solid electrolyte which is often used by many research groups for different FIBs operating at RT, mechanochemically synthesized NH4Sn2F5 has a great potential to be tested as a solid electrolyte in both conversion type and intercalation type FIBs because of its higher RT conductivity value arising from the motion of F ions.