Ion-conducting Membrane Research Articles

Electrochemical Corrosion Measurements in Supercritical Carbon Dioxide - Water Systems with and Without Membrane Coating

Growing interest in transporting supercritical carbon dioxide (scCO2) for enhanced oil recovery and carbon capture and storage has led to an increased interest in the corrosion behavior of pipeline steels at varying levels of water contamination. While there has already been substantial investigation of aqueous phase corrosion under scCO2 saturation, there has been little to no analysis of the kinetics of the charge transfer process in such environments. Additionally, our group has recently presented a probe for making measurements in the non-conductive scCO2 bulk phase when contaminated by water vapor. This was accomplished by coating the probe tip with an ion conductive membrane, though it was not determined whether the presence of this membrane in any way affected the observed corrosion behavior. The work presented here serves to both increase the knowledge of charge transfer kinetics in water-scCO2 corrosion and examine the influence of ion conductive membranes on the corrosion process.

Ion Motion in Anion and Proton-Conducting Triblock Copolymers

To learn more about anion transport in functionalized polymers and improve anion exchange membrane (AEM) performance, we have directly compared the properties of proton exchange membranes (PEMs) and AEMs. A single batch of poly(hexyl methacrylate)-b-poly(styrene)-b-poly(hexyl methacrylate), PHMA-b-PS-b-PHMA, triblock copolymer was synthesized and postfunctionalized in the PS block with sulfonate or quaternary ammonium moieties. The conductivity, water uptake, and morphology of low, middle, and high IEC anionic and cationic PHMA-b-PS-b-PHMA triblock copolymers were investigated, and the metrics of ion diffusivity and membrane sensitivity to relative humidity are introduced. We observed that these block copolymer AEMs and PEMs had similar values for the ratio of calculated ion diffusion coefficient to the mobile species dilute ion diffusivity (D/D0) as a function of hydration. This observation points to similar morphological barriers to transport and similar hydration dependence in each material and provides a basis for understanding ion transport in AEMs compared to dilute solution. As the ion concentration in the functionalized block was increased, the sensitivity of conductivity to relative humidity decreased due to closer proximity of the ionic groups. These guidelines for AEM design will help to more deeply understand the similarities and differences between different types of water-absorbing, ion-conducting membranes.

Layered Ultrathin Ion Conductive Membrane Using Polymer Nanosheet with Amine Group

Layered ultrathin ion conductive membrane was prepared using poly (N-dodecylacrylamide-co-N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)acrylamide) (p(DDA/ DONH)) polymer nanosheet. The polymer forms a stable monolayer at the air-water interface and is transferable to a solid substrate using the Langmuir-Blodgett technique. The multilayer film showed a clear layered structure with 2.0 nm periodicity confirmed by X-ray diffraction measurements. The polymer nanosheet showed ion conductivity of 0.85 × 10−3 S/cm at 100% RH with 20°C through the layer plane direction.

Oxygen Permeation from Oxygen Ion-Conducting Membranes Coated with Porous Metals or Mixed Ionic and Electronic Conducting Oxides

Increasing oxygen permeation from oxide membranes can enable the development of next-generation power generation technologies with high efficiency and reduced CO2 mission. Here we introduce a new approach to design oxygen permeation membranes by covering the surfaces of pure oxygen-ion conductors with porous precious metal (Au and Ag) network or MIECs (LNO and LSCF). Oxygen permeation flux was enhanced by greatly by coating porous silver on the whole surface of pure oxygen ion-conducting membranes such as Zr0.85Y0.16O2-δ (YSZ), Bi1.5Er0.5O3 (BE25), and La0.8Sr0.2Ga0.8Mg0.115Co0.085O3-δ (LSGMC). Oxygen permeation flux of La2NiO4+δ (LNO)-sputtered LSGMC membranes was comparable to silver-coated LSGMC membranes which demonstrates that membranes devoid of the use of noble metal can be prepared using this geometry. In contrast, oxygen permeation fluxes of YSZ and BE25 membrane did not increase by sputtering LNO or LSCF film because of the reaction between the membrane and LNO or LSCF. We obtained an oxygen permeation flux of 2.2 × 10−8 cm−2 s−1 at 700°C by coating porous silver on the feed side of LNO-sputtered LSGMC membrane, which was comparable to that of LNO membrane. The rate-limiting process for oxygen permeation through these membranes will be discussed.

Stable and hydroxide ion conductive membranes for fuel cell applications: Chloromethyaltion and amination of poly(ether ether ketone)

Poly(ether ether ketone) (PEEK) was dissolved in conc. H2SO4 and its chloromethylation was achieved in presence of paraformaldehyde, trimethylchlorosilane and Lewis acid catalyst, obtained about 35–75% degree of chloromethylation (DCM). This idea is based on partial sulfonation of PEEK to make it soluble and further complete replacement of –SO3H with –CH2Cl groups. Alkaline membranes (AMs) were prepared by quaternization of chloromethylated PEEK (CMPEEK). The reported method is a “green” alternative for the production of AEM without the use of hazardous chemicals (such as chloromethyl methyl ether, chloromethyloctylether, bis(chloromethyl) ether etc.). Chronopotentiometry study of prepared membranes confirmed their homogeneous and alkaline nature suitable for methanol fuel cells. The AMs exhibit a splendid chemical stability at 10M KOH. Alkaline conductivity of quaternized poly(ether ether ketone) membrane with 75% DCM (QPEEK-75) (14.63mScm−1) in equilibration with deionized water was relatively high in compare with other AMs reported in the literature. For the H2/air single fuel cell at 50°C with QPEEK-75 membrane, about 1.02V OCV and 48.09mWcm−2 power density at 109.3mAcm−2 current density were obtained.

Theory and computational study of electrophoretic ion separation and focusing in microfluidic channels

In this work we describe the theory and 2D simulation of ion separation and focusing in a new concept of microfluidic separation device. The principle of the method of ion focusing is classical in the sense that it consists in opposing a hydrodynamic transport ensured by the solution flow to an electrophoretic driving force so that any ionic sample results poised within the microchannel at the point where the two forces equilibrate. The originality of the concept investigated here relies on the fact that thanks to the use of an ion-conducting membrane of variable thickness in electrical contact with the channel the electrophoretic force is varied continuously all along the channel length. Similarly, changing the geometric shape of the membrane allows a facile optimization of the device separation and focusing properties.

Effect of compression on PFSA-ionomer morphology and predicted conductivity changes

Ion-conductive membranes used in energy devices are always under compression to minimize a device's contact resistance. In this paper, the conductivity and nanostructure of Nafion membrane, a commonly used ionomer in many electrochemical energy applications, are investigated under compression. Hydrophilic-domain spacing as a function pressure is determined both in the plane (face-on imaging) and thickness (edge-on imaging) directions using small-angle X-ray scattering (SAXS). SAXS results suggest a similar nanostructure in all directions indicating lack of a strong anisotropy when not under compression. However, compressing the membrane induces structural anisotropy where domain spacing gets smaller in the compression (thickness) direction while it elongates in the plane of the membrane. From the domain spacing and water content under compression, the change in conductivity is calculated as a function of pressure and compared with measured data. The findings of this work provide insight into the effect of compression on the three-dimensional morphology of a PFSA membrane and its conductivity, issues that have not been previously explored and are critical to the understanding of ion-conductive membranes.

A study of electrodialysis operating with mixed flow mode

Electrodialysis (ED) is a separation technique in which an electrical field is used to transport anions and cations through ion conductive membranes positioned between two adjacent compartments, often in view of desalination. ED forces ions to move from a low concentration compartment (diluate) to a high concentration compartment (concentrate). A co-current hydraulic flow mode of the salt solutions through the ED stack compartments is often applied. Under such conditions and considering the practical dimensions of industrial ED stacks, a series of stacks is mostly required in order to obtain a specified level of desalination in the diluate. A co-current hydraulic flow mode is common practice in ED but the approach can result in a high concentration difference between concentrate and diluate in the final stacks, which is disadvantageous. In this paper, the theoretical and practical implications of changing the classic co-current hydraulic flow mode into a mixed flow mode are studied. In such a mixed flow mode the internal hydraulic flow of diluate and concentrate is co-current in the stack compartments but is externally counter-current over the total series of stacks. The mixed flow mode favors a much lower concentrate and diluate concentration difference within each stack when compared to the full co-current mode. Additional advantages by introducing the feed&bleed principle in the concept are demonstrated too.

Synthesis and study of oxide and phosphor-silicate nanocomposites for the creation of new-generation supercapacitors

Using the methods of joint precipitation of hydroxides and joint crystallization of nitrate solutions, nanocrystalline ceramics have been synthesized on the basis of lanthanum and neodymium chromites and the two-phase composition (ZrO2)0.6(In2O3)0.4 with average grain sizes of 80–90 and 50–60 nm, respectively. Nanoceramics possess electrical conductivity from 10−2 to 10 S cm−1 in the temperature range 20–800°C. Ion-conducting membranes compatible with the obtained electrode ceramics have been synthesized by the sol-gel method from silica gels doped with orthophosphoric acid.

Engineering the Van der Waals Interaction in Cross‐Linking‐Free Hydroxide Exchange Membranes for Low Swelling and High Conductivity

What a swell for hydroxides: The typical trade-off between swelling control and ion conductivity in ion-conducting polymer membranes is overcome by enhancement of van der Waals interactions among polymer chains. Using a quaternary phosphonium-functionalized polymer, the simple combination of high electron density of the polymer and large dipole moment of the functional group leads to low membrane swelling, high hydroxide conductivity, and excellent hydroxide exchange membrane fuel cell performance.

Electrochemical studies of nafion–trimethylsilyl and nafion–trimethylsilyl/Ru complex-modified electrodes

In this work, we report the electrochemical properties of the nafion–trimethylsilyl (Naf–TMS) polymer. First, we introduce a procedure to dissolve Naf–TMS polymer and the incorporation of ruthenium catalyst complexes into it. The inclusion of the catalysts involved two strategies. The first one concerned the direct formation of a Naf–TMS/Ru complex solution. The second one consists of depositing Naf–TMS solution on a glassy carbon electrode, followed by the incorporation of Ru complexes under potentiodynamic conditions. Electrochemical studies showed the good ion permeation capability of Naf–TMS membranes and its use as a good alternative approach to Nafion ion-conducting membranes. The analytical capabilities of Naf–TMS- and Naf–TMS/Ru-modified glassy carbon electrodes have been tested for the detection of dopamine in standard solutions. Detection limits in the order of nanomolar have been achieved with working ranges extending over three decades in concentration at pH 7.2. Further enhancement in the dopamine oxidation current was achieved by the incorporation of Ru complexes into the Naf–TMS polymer. This study offers a new insight into the investigation of Naf–TMS resin as an ion-conducting polymer.

Ion-Conducting Membranes Based on Gelatin and Containing LiI/I2 for Electrochromic Devices

Ionic conducting membranes of gelatin plasticized with glycerol and containing LiI/I2 have been obtained and characterized by X-ray diffraction measurements, UV-Vis-NIR spectroscopy, thermal analysis and impedance spectroscopy. The transparent (80–90% in the visible range) membranes showed ionic conductivity value of 5 × 10−5 S/cm at room temperature, which increased to 3 × 10−3 S/cm at 80°C. All the ionic conductivity measurements as a function of temperature showed VTF dependence and activation energy of 8 kJ/mol. These samples also showed low glass transition temperature of −76°C. Moreover the samples were predominantly amorphous. The membranes applied to small electrochromic devices showed 20% of color change from colored to bleached states during more than 70 cronoamperometric cycles.

All-solid-state proton conductive membranes prepared by a semi-interpenetrating polymer network (semi-IPN)

Novel all-solid-state ion conductive polymer membranes were synthesized for anhydrous high temperature fuel cells. Ion-conductive monomers (ethylene glycol methacrylate phosphates, phosmers) were employed for fixing ion-conductive moieties in the matrix polymer (sulfonated poly(arylene sulfone), sPAS). Inorganic materials, acid-doped titanium oxide and tin indium phosphate were introduced to form anhydrous polymer composite membranes. As a result, poly(phosmer)s significantly improved both the proton conductivity and flexibility of the composite membranes. Sulfonated poly(arylene sulfone)–poly(phosmer)–tin indium phosphate composite membranes showed the highest ion-conductivity value under anhydrous conditions due to the dipolar interaction of poly(phosmer) with the matrix polymer and the inorganic material. The composite membranes exhibited a drastic enhancement in performances of anhydrous high temperature fuel cells compared to those of Nafion-based composite membranes. The fuel cell performances indicate that the poly(arylene sulfone)–poly(phosmer)–inorganic particle composites could be applicable for anhydrous high temperature fuel cells as promising polymer electrolyte membranes.

Remodeling the host environment: modulation of the gastric epithelium by the Helicobacter pylori vacuolating toxin (VacA)

Virulence mechanisms underlying Helicobacter pylori persistence and disease remain poorly understood, in part, because the factors underlying disease risk are multifactorial and complex. Among the bacterial factors that contribute to the cumulative pathophysiology associated with H. pylori infections, the vacuolating cytotoxin (VacA) is one of the most important. Analogous to a number of H. pylori genes, the vacA gene exhibits allelic mosaicism, and human epidemiological studies have revealed that several families of toxin alleles are predictive of more severe disease. Animal model studies suggest that VacA may contribute to pathogenesis in several ways. VacA functions as an intracellular-acting protein exotoxin. However, VacA does not fit the current prototype of AB intracellular-acting bacterial toxins, which elaborate modulatory effects through the action of an enzymatic domain translocated inside host cells. Rather, VacA may represent an alternative prototype for AB intracellular acting toxins that modulate cellular homeostasis by forming ion-conducting intracellular membrane channels. Although VacA seems to form channels in several different membranes, one of the most important target sites is the mitochondrial inner membrane. VacA apparently take advantage of an unusual intracellular trafficking pathway to mitochondria, where the toxin is imported and depolarizes the inner membrane to disrupt mitochondrial dynamics and cellular energy homeostasis as a mechanism for engaging the apoptotic machinery within host cells. VacA remodeling of the gastric environment appears to be fine-tuned through the action of the Type IV effector protein CagA which, in part, limits the cytotoxic effects of VacA in cells colonized by H. pylori.

Modeling of IPMC (Ionic Polymer-Metal Composite) Sensor to Effectively Detect the Bending Angles of a Body

Ionic polymer-metal composite(IPMC) consists of an ion conductive membrane plated by metallic electrodes on both surfaces. When it bends, a voltage is generated between two electrodes. Since IPMC is flexible and thin, it can be easily mounted on the various surfaces of a body. The present study investigates a sensor system using IPMC to effectively detect the bending angles applied on IPMC sensor. The paper evaluates several R and C circuit models that describe the physical composition of IPMC and selects the best model for the detection of angles. The circuit models implemented with a charge model describe the relationship between input bending angles and output voltages. The identification of R and C values was performed by minimizing the error between the real output voltages and the simulated output voltages from the circuit models of IPMC sensor. Then the output signal of a sensor was fed into the inverse model of the identified model to reproduce the bending angles. In order to support the validation of the model, the output voltages from an arbitrary bending motion were also applied to the selected inverse model, which successfully reproduced the arbitrary bending motion.

Transient Receptor Potential Melastatin 1 (TRPM1) Is an Ion-conducting Plasma Membrane Channel Inhibited by Zinc Ions

TRPM1 is the founding member of the melastatin subgroup of transient receptor potential (TRP) proteins, but it has not yet been firmly established that TRPM1 proteins form ion channels. Consequently, the biophysical and pharmacological properties of these proteins are largely unknown. Here we show that heterologous expression of TRPM1 proteins induces ionic conductances that can be activated by extracellular steroid application. However the current amplitudes observed were too small to enable a reliable biophysical characterization. We overcame this limitation by modifying TRPM1 channels in several independent ways that increased the similarity to the closely related TRPM3 channels. The resulting constructs produced considerably larger currents after overexpression. We also demonstrate that unmodified TRPM1 and TRPM3 proteins form functional heteromultimeric channels. With these approaches, we measured the divalent permeability profile and found that channels containing the pore of TRPM1 are inhibited by extracellular zinc ions at physiological concentrations, in contrast to channels containing only the pore of TRPM3. Applying these findings to pancreatic β cells, we found that TRPM1 proteins do not play a major role in steroid-activated currents of these cells. The inhibition of TRPM1 by zinc ions is primarily due to a short stretch of seven amino acids present only in the pore region of TRPM1 but not of TRPM3. Combined, our data demonstrate that TRPM1 proteins are bona fide ion-conducting plasma membrane channels. Their distinct biophysical properties allow a reliable identification of endogenous TRPM1-mediated currents.

Zeta Potential of Ion-Conductive Membranes by Streaming Current Measurements

Surface charge properties have a significant influence on membrane retention and fouling performance. As a key parameter describing the surface charge of membranes used in aqueous applications, zeta potential measurements on membranes of various types have attracted great attention. During the zeta potential characterization of a series of ion-conductive sulfonated poly(sulfone) membranes, it was found that the measured streaming current varied with the thickness of the sample, which is not predicted by the classical Smoluchowski equation. Moreover, for higher conductivity membranes with an increased concentration of sulfonate groups, the zeta potential tended toward zero. It was determined that the influence of membrane bulk conductance on the measured streaming current must be taken into account in order to correctly interpret the streaming current data for ion-conductive polymers and understand the relationship between membrane chemical composition and zeta potential. Extrapolating the measured streaming current to a membrane thickness of zero has proven to be a feasible method of eliminating the error associated with measuring the zeta potential on ion conductive polymer membranes. A linear resistance model is proposed to account for the observed streaming currents where the electrolyte channel is in parallel with the ion-conductive membranes.

Fluorene-containing cardo polymers as ion conductive membranes for fuel cells

For polymer electrolyte fuel cells, proton conducting electrolyte membranes are key materials. This review highlights aromatic polymers containing cardo groups and ionic functions as emerging electrolyte materials. First, the role of biphenyl fluorene groups on sulfonated polyimides is discussed. Discussion then focuses on how to balance proton conductivity and membrane stability with sulfonated poly(arylene ether)s making the most of the bulky cardo groups. Block copolymer structure containing fully sulfonated biphenyl fluorene groups in its hydrophilic component and compact hydrophobic component is proposed. Effect of superacid groups onto the properties of fluorene-containing polymers is discussed. Replacing sulfonic acid groups with ammonio groups afforded the cardo polymers highly anion conducting properties, which make them potentially applicable to alkaline fuel cells.

Sodium-beta alumina batteries: Status and challenges

This paper provides a review of materials and designs for sodium-beta alumina battery technology and discusses the challenges ahead for further technology improvement. Sodium-beta alumina batteries have been extensively developed in recent years and encouraging progress in performance and cycle life has been achieved. The battery is composed of an anode, typically molten sodium, and a cathode that can be molten sulfur (Na-S battery) or a transition metal halide incorporated with a liquid phase secondary electrolyte (e.g., ZEBRA battery). In most cases the electrolyte is a dense solid β″-Al2O3 sodium ion-conducting membrane. The issues prohibiting widespread commercialization of sodium-beta alumina technology are related to the materials and methods of manufacturing that impact cost, safety, and performance characteristics.

Performances of tubular La 0.8Sr 0.2Fe 0.7Ga 0.3O 3− δ mixed conducting membrane reactor for under pressure methane conversion to syngas

The performances of the Mixed oxygen Ion and Electronic Conducting (MIEC) membrane reactor with surface catalyst was investigated for the methane conversion to synthesis gas, at operating conditions as close as possible to industrial requirements (pressurized syngas, high temperature, CH 4 + H 2O mixture as feed). A dense self supported tubular membrane in one closed end geometry, made from the perovskite composition La 0.8Sr 0.2Fe 0.7Ga 0.3O 3− δ (LSFG), was elaborated by isostatic pressing and was coated with a La 0.8Sr 0.2Fe 0.7Ni 0.3O 3− δ (LSFN) porous catalyst. Results show that LSFG membrane can be operated under pressure and pure methane as dry feed for more than 142 h without any fracture. Moreover, syngas production (X(CH 4) and S(CO)) are greatly related to the reactor design and feed contact time. As a result, CH 4 conversion, CO selectivity, and oxygen permeation flux through the membrane can reach respectively 74%, 50% and 0.9 N m 3/m 2 h at 1173 K, with CH 4 + H 2O mixture, S/C = 1 (Steam/Carbon ratio), P Feed = 0.3 MPa and a feed contact time of 13 s. Microstructure observations have shown Ni metallic exudation from LSFN surface catalyst and strontium rich continuous layer at catalyst/membrane interface under working conditions. However, these chemical/structural modifications did not seem to be detrimental to performances during short test duration (142 h).