Ion-conducting Membrane Research Articles

Hydrogen production by water dissociation using mixed conducting dense ceramic membranes

Significant amounts of hydrogen or oxygen can be generated at moderate temperatures (500–900 °C) if a mixed-conducting (i.e., electron- and ion-conducting) membrane is used to remove either oxygen or hydrogen as it is generated. We demonstrated this in a previous study using cermet (i.e., ceramic–metal composite) membranes composed of an oxygen ion conductor, Gd-doped CeO 2 (CGO), and an electronic conductor, Ni. In the present study, we show several ways to increase the hydrogen production rate by water dissociation with mixed-conducting membranes. Producing CGO/Ni membranes with a finer microstructure enlarged the triple-phase-boundary area, and increased the hydrogen production rate to ≈ 10 cm 3 ( STP ) / min - cm 2 . Using a single-phase, mixed-conducting membranes [ SrFeCo 0.5 O x ( SFC 2 ) ] also produced higher hydrogen production rates, relative to dual-phase cermet membranes.

Application of oxygen ion-conductive membranes for simultaneous electricity and hydrogen generation

The high temperature of the air in power generation gas-turbine cycles involving natural gas (mainly methane) oxidation accounts for the utilization of ion-conductive membranes within solid oxide fuel cells (SOFCs) and membrane reactors (MRs). In SOFCs, the electricity is directly derived from the chemical exergy of methane (SOFCs with internal methane reforming are considered here). Within a membrane reactor (MR), which is considered a substitute for combustion chambers in traditional gas-turbine units, the ion-conductive membranes separate oxygen from air and allow the flow of the hot combustion products (carbon dioxide and steam) to be separated from air. It permits the use of combustion products which are not diluted in nitrogen in the process of methane conversion into hydrogen. A modified gas-turbine cycle that includes a SOFC stack, an MR (instead of a traditional combustion chamber), and a catalytic reactor to convert methane to hydrogen is proposed. An exergy analysis of the proposed system is conducted to evaluate its exergy efficiency and the exergy losses for the processes occurring within the system. It is shown that, in comparison to the traditional gas-turbine cycle, there is a significant reduction (more than three times) in the exergy losses for the most irreversible process occurring in the system, natural gas combustion. It is also found that the proposed cogeneration scheme, including both power generation and the industrial catalytic conversion of methane to hydrogen, permits improved efficiencies for both technologies. The efficiency of this cogeneration, as well as the reduction in exergy losses, is demonstrated by the following observation: if the value of energy (exergy) efficiency of hydrogen production is considered equal to that for a traditional process, the corresponding thermal (energy) efficiency for electricity generation would reach values of 80–96% depending on the efficiency of a SOFC stack. The combined SOFC and MR application also eliminates the possibility of toxic nitrogen oxides formation and, at the same time, makes carbon dioxide removal from flue gases feasible (due to its high concentration). The development of the proposed technology is especially important, within the context of the hydrogen economy, if the produced hydrogen is used as a fuel for fuel cell vehicles.

Progress in three-dimensional (3D) Li-ion microbatteries

Progressing from 2D to 3D thin-film microbattery structures represents an important paradigm shift in the development of electrochemical power sources. The development process of three-dimensional microbatteries (3D-MB) on a perforated substrate has to solve complicated technical barriers, such as insertion and deposition of a sandwich of high-capacity thin cathode and ion-conducting membrane in long (500 μm) and narrow (< 50 μm) channels. In this study, we investigate composite thin-film cathodes that allow 2.0–3.5 times increase of MB capacity for a given footprint over our previous 3D-MB with conventional thin-film battery cathodes. The composite cathodes are obtained by electrodeposition from the bath modified by PEGDME and PEO additives of different molecular weights and concentrations. SEM, XPS, TOFSIMS and electrochemical characterizations were performed to elucidate the source of the improved MB performance. Experimental results obtained in this work show that the addition of polymeric compounds to the electrolytes significantly improves the structure and electrochemical behavior of electrodeposited molybdenum sulfide cathode materials. A semi-3D-on-MCP cell with a composite cathode exhibits a stable cycle life with about 3.5 mA h/cm 2 reversible capacity, 20 to 30 times that of a planar 2D thin-film cell with the same footprint and about twice that of semi-3D cells with pristine cathodes.

Use of nano-composite component to improve the conductivity and mechanical properties of Li 2SO 4–Al 2O 3 solid electrolyte

The microstructure, density, and conductivity of Li 2SO 4 ion-conducting membranes incorporating nano-composite Li 2SO 4–Al 2O 3 prepared using a sol–gel technique are superior to membranes having the same bulk composition prepared from mixtures of lithium sulfate and fine alumina powder. Properties of membranes made from the nano-composite material depend on both the overall composition and the preparative parameters. The relationships between preparative parameters, microstructure, and properties have been determined, from which we have found the optimum lithium sulfate content and thermal treatment parameters for manufacture of membranes with minimum gas permeability and maximum ionic conductivity.

A simple statistical approach to the boyer model of the molecular motor adenosine triphosphatase

A physical description of the F0F1 adenosine triphosphatase as a rotating motor is proposed. The catalytic center and the ion-conducting membrane are considered within the classical Boyer model for the rotor and the catalytic parts of the motor, thereby allowing application of a simple three-pole model, which decreases the number of parameters significantly. The stochastic character of the processes occurring in motors is described by the Fokker-Planck equations. Various dependences of the rotation speed on the degree of excitation, localization of excitations, and the amplitude of the potential are reported.

Economic and environmental comparison of conventional, hybrid, electric and hydrogen fuel cell vehicles

Published data from various sources are used to perform economic and environmental comparisons of four types of vehicles: conventional, hybrid, electric and hydrogen fuel cell. The production and utilization stages of the vehicles are taken into consideration. The comparison is based on a mathematical procedure, which includes normalization of economic indicators (prices of vehicles and fuels during the vehicle life and driving range) and environmental indicators (greenhouse gas and air pollution emissions), and evaluation of an optimal relationship between the types of vehicles in the fleet. According to the comparison, hybrid and electric cars exhibit advantages over the other types. The economic efficiency and environmental impact of electric car use depends substantially on the source of the electricity. If the electricity comes from renewable energy sources, the electric car is advantageous compared to the hybrid. If electricity comes from fossil fuels, the electric car remains competitive only if the electricity is generated on board. It is shown that, if electricity is generated with an efficiency of about 50–60% by a gas turbine engine connected to a high-capacity battery and an electric motor, the electric car becomes advantageous. Implementation of fuel cells stacks and ion conductive membranes into gas turbine cycles permits electricity generation to increase to the above-mentioned level and air pollution emissions to decrease. It is concluded that the electric car with on-board electricity generation represents a significant and flexible advance in the development of efficient and ecologically benign vehicles.

Synthesis of Pendent Functionalized Cyclotriphosphazene Polyoctenamers: Amphiphilic Lithium Ion Conductive Materials

The synthesis of novel polyoctenamers with pendent functionalized cyclotriphosphazenes as amphiphilic lithium ion conductive membranes is described. Cyclotriphosphazene monomers were functionalized with one cycloocteneoxy substituent per ring. Two different types of monomer units, one with oligoethyleneoxy cation coordination side groups and the other with hydrophobic fluoroalkoxy side groups, were then prepared. The syntheses of these monomers, their ring-opening metathesis copolymerization, and the characteristics of the resultant polymers are discussed, with an emphasis on the dependence of ionic conductivity and hydrophobicity on polymer composition.

Preparation of three dimensionally ordered macroporous Li0.35La0.55TiO3 by colloidal crystal templating process

Three dimensionally ordered macroporous Li+ ion conductive membranes of Li0.35La0.55TiO3 were prepared by a colloidal crystal templating method combined with sol–gel process. Colloidal crystal composed of monodisperse polystyrene particles (3 μm diameter) was utilized as a template. Sol of Li–La–Ti–O was prepared from lithium acetate, lanthanum acetate, and titanium tetraisopropoxide. The sol was injected into the template, and it was converted to gel. Polystyrene particles were removed by calcinations at high temperatures, and then macroporous Li0.35La0.55TiO3 was obtained. Li+ ion conductivity in the crystal grain part of Li0.35La0.55TiO3 annealed at 1000 °C was 2×10−4 S cm−1 at room temperature.

Effect of reactor dimensions on the performance of an O [formula omitted] pump integrated partial oxidation reformer—a modelling approach

This paper describes a two-dimensional model of an oxygen permeable membrane reactor for partial oxidation of methane (POM). The model covers all aspects of major chemical kinetics, heat and mass transfer phenomena in the tubular reactor with oxygen permeation in radial direction through an ion-conducting membrane. The temperature and concentrations of the major species in the membrane tube were calculated. Results showed that the overall performance of the reactor was strongly dependent on the reactor dimensions and operating conditions. A reactor with smaller diameter ( D) and greater length-to-diameter ratio ( L/ D) gives better performance in terms of high methane (CH 4 ) conversion and high hydrogen (H 2 ) concentration. Under inlet gas temperature of 900 K and space velocity of 15,000 h - 1 , the CH 4 conversion and dry H 2 concentration can reach 98% and 64%, respectively, in the reactor with diameter D around 10 mm and L/D > 25 .

Applicability of emf measurements under external load resistance conditions for ion transport number determination

In order to evaluate the applicability of concentration cells for the ion transference number measurements with external load, the cell response was simulated with variable transport properties of the cell material, external load resistance, geometrical factors such as ion-conducting membrane thickness, and electrode kinetics. This technique is expected to be pertinent when ηF/RT<0.2, except possibly for conditions when the electrode kinetics is dependent on a relatively small limiting current density. In each particular case, the method validity can be verified by testing if the overpotential sum grows faster than current on decreasing the external load resistance. A pyrochlore-type material Gd1.9Ca0.1Ti2O7-δ with dominant oxygen ionic conductivity is used as a study case to demonstrate the criteria proposed to assess the applicability of emf measurements under short-circuit conditions.

Synthesis and oxygen transport characteristics of dense and porous cerium/gadolinium oxide materials: Interest in membrane reactors

Cerium/gadolinium oxide (CGO)-based ceramic ion conductive membranes (CICMs) have potential uses in catalytic membrane reactors (CMRs) and solid oxide fuel cells (SOFCs). A supercritical CO 2 aided sol–gel process allowed the synthesis of CGO materials with the composition Ce 0.9Gd 0.1O 1.95. The produced nanophase powders were non-agglomerated, with a controlled morphology, a high purity and a high specific surface area (>100 m 2/g). The CGO cubic crystalline phase has been obtained at temperatures <300 °C, lower than those of conventional solid state chemistry routes. With respect to ionic oxygen transport, a high conductivity at intermediate temperature (2 × 10 −2 S cm −1 at 600 °C), almost equivalent in dense and porous samples, has been obtained on sintered materials prepared from these powders. In relation to their porosity characteristics, a modelling approach successfully explained the high ionic oxygen transport of some specific porous samples. Future directions for preparing porous conductive ceramics well adapted to CMR or SOFC applications can be anticipated from this model.

Designing a New Generation of Proton-Exchange Membranes Using Layer-by-Layer Deposition of Polyelectrolytes

All fuel cells utilizing the membrane-electrode assembly have their ion-conductive membrane sandwiched between bipolar plates. Unfortunately, applying conventional techniques to isolated polyelectrolyte membranes is challenging and difficult. A more practical alternative is to use the layer-by-layer assembly technique to fabricate a membrane-electrode assembly that is technologically relatively simple, economic, and robust. The process presented here paves the way to fabricate ion-conductive membranes tailored for optimum performance in terms of controlled thickness, structural morphology, and catalyst loading. Composite membranes are constructed through the layered assembly of ionically conductive multilayer thin films atop a porous polycarbonate membrane. Under ambient conditions, a fuel cell using a poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) composite membrane delivers a maximum power density of 16.5 mW cm–2 at a relative humidity of 55 %, which is close to that of some commercial fuel cells operating under the same conditions. Further optimization of these systems may lead to new, ultrathin, flexible fuel cells for portable power and micropower applications.

Kinetic Modelling of Partial Oxidation of Methane in an Oxygen Permeable Membrane Reactor

A two-dimensional unsteady-state heterogeneous model has been developed to simulate an oxygen permeable membrane (CH4) reactor for partial oxidation of methane (POM) with steam added. The model covers all aspects of major chemical kinetics, heat and mass transfer phenomena in the tubular reactor with oxygen permeation in radial direction through an ion-conducting membrane. The temperature and concentrations of the major species in the membrane tube (catalyst bed) and air region were calculated. Results showed that radial oxygen permeation would cause a little maldistribution of gas concentrations in the radial direction of the reactor under study. The overall performance of the reactor was found to be closely dependent on its feeding and operating conditions. Improved performance in terms of high methane (CH4) conversion, high hydrogen (H2) yield and low carbon monoxide (CO) concentration can be achieved when the reactor operates at inlet gas temperature from 900 K to 1000 K, water to fuel (W/F) ratio of round two and gas hour space velocity of about 20 000/h.

The use of dense mixed ionic and electronic conducting membranes for chemical production

The exploitation of membranes within the chemical industry is an area of growing interest. Inorganic membranes promise high stabilities even under high temperature conditions (>200 °C). In addition, very high selectivities can be attained when dense ion-conducting membranes are employed. Here the characterisation of such dense inorganic membranes, through permeation studies, and the application of these membranes in chemical production are reviewed. Additional background information on membrane fabrication and techniques for characterisation is also provided.

Oxidation of Dry Methane on the Surface of Oxygen Ion-Conducting Membranes

The surface exchange limitations of oxygen permeation through dense mixed-conducting membranes enhance membrane stability, enabling the operation of mixed conductors, such as La0.3Sr0.7Co0.8Ga0.2O3-δ (LSCG) and La2Ni0.9Co0.1O4+δ (LNC), under air/dry CH4 gradient up to temperatures as high as 1173–1223 K. Testing of these materials in a model disk-shaped membrane reactor at 1023–1223 K showed high CO2 yields (>75%). In particular, at 1173 K, the CO selectivity was 17% for LNC and 2% for LSCG ceramics, with methane conversion efficiency of 20 and 37% respectively. Similar tendency was observed for a fuel cell-type reactor with yttria-stabilized zirconia solid electrolyte and cermet Ce0.8Gd0.2O2-δ/Pt anode, where decreasing the molar ratio between methane and electrochemically supplied oxygen from approximately 10 to 2 decreases CO/CO2 ratio at the outlet down to 0.3. This behavior suggests significant role of the complete methane oxidation on the interface between an oxygen ion-conducting membrane and gas phase, thus making it necessary to incorporate reforming catalysts in the reactors.

Plasma polymerized electrolyte membranes and electrodes for miniaturized fuel cells

Miniaturized fuel cells for portable systems like cellular phones, laptops, or other conventionally battery-driven devices, as well as long-term stationary monitoring electronics, have a potential market, especially for direct methanol fuel cells. However, design and fabrication technologies have to be adopted that allow the desired miniaturization of such a fuel cell. Thin film technologies like plasma polymerization and sputtering are suitable techniques for realizing membrane electrode assemblies only several microns in thickness that can be deposited on thin substrates (e.g., silicon wafers, porous foils, or others). Furthermore, plasma polymerized films exhibit a high degree of cross-linkage and are pinhole free even for films of only a few hundred nanometer in thickness, in contrast to conventionally polymerized films. In case of an electrolyte membrane these benefits yield a reduction of membrane resistance and a decreased methanol crossover. We have developed plasma polymerized electrolyte membranes using tetrafluoroethylene to generate the polymeric backbone of an ion-conductive membrane and vinylphosphonic acid to incorporate acid groups, which are responsible for the proton conductivity. Depending on the process parameters these films exhibit an ion conductivity in the range of 100 mS/cm to 200 mS/cm (at 80°C), determined by ac-impedance measurements. These films were optimized with respect to their use in direct methanol fuel cells to achieve a high ion conductivity and high thermal resistance. Porous graphite electrodes were fabricated using an acetylene plasma polymerization process. These films are combined with the plasma polymerized electrolyte membrane to form a thin film membrane electrode assembly.

Fuel Cells, Advanced Reactors and Smart Catalysis: The Exploitation of Ceramic Ion‐Conducting Membranes

AbstractMembrane reactors are of great interest in the chemical industries because they offer the possibility of improved yields, improved selectivities and more compact plant. However, a significant barrier to their uptake is the unavailability of membrane systems having the required performance at an acceptable cost. In this paper we will explore the use of one class of membrane that has the potential to deliver high performance at reasonable cost. Ion‐conducting ceramic membranes can be used in a wide range of high temperature applications including fuel cells, advanced reactors and even smart catalytic systems.

Patents

High-strength asymmetric cellulose membranes Membrane for the treatment of waste lubricants Cross-linked polymer blend membrane Ceramic membrane Gas chromatograph calibration Sugar preparation Crosslinked sulphonated polyimide films Graft copolymer membranes Water supply system Hydrophilic polymers Ion-conducting membrane Polymerization reactors Water purification cartridge Self-contained water filter with zeolites Multiple-well sequencing plate Semi-permeable composite membrane Membrane body Down-hole gas separation system Microfabricated nanopore device for sustained release of therapeutics Apparatus and method for cleaning membrane filtration modules

Ion conductive electrolyte membranes based on co-continuous polymer blends

Download options Please wait... Article information DOI https://doi.org/10.1039/B304462A Article type Paper Submitted 23 Apr 2003 Accepted 02 Jul 2003 First published 04 Aug 2003 Download Citation J. Mater. Chem., 2003,13, 2168-2176 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Ion conductive electrolyte membranes based on co-continuous polymer blends A. Munch Elmér, B. Wesslén, P. Sommer-Larsen, K. West, H. Hassander and P. Jannasch, J. Mater. Chem., 2003, 13, 2168 DOI: 10.1039/B304462A To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Anette Munch Elmér Bengt Wesslén Peter Sommer-Larsen Keld West Helen Hassander Patric Jannasch

Preparation and Characterization of Lithium Ion Conductive Membranes Constructed from Three-Dimensional Ordered Porous Material

Preparation and Characterization of Lithium Ion Conductive Membranes Constructed from Three-Dimensional Ordered Porous Material