New oxide ion conductors with perovskite structures containing alkali metal were explored for use as solid support materials for MCFCs (molten carbonate fuel cells). The conductivity of two candidates, BNT (0.94Bi0.5Na0.5TiO3-0.06BaTiO3) and LNT (La0.5Na0.5TiO3), in an oxidation atmosphere, were measured and compared. The conductivity measurement of BNT in a reducing atmosphere indicated the reduction of BNT to Bi metal by a sharp change in conductivity. It limited the lifetime of the fuel cell using BNT as solid support. Fuel cell measurements using the alternative perovskite LNT showed excellent stability under fuel cell operation conditions and high-power density compared to conventional MCFC with LiAlO2 as the solid matrix. The reason for obtaining high electrochemical performance using the LNT matrix is discussed.

https://doi.org/10.1016/j.fuel.2024.132144

A numeric scale of acidity and basicity, developed by D.W. Smith, allows for quantitative comparison between different oxides and has been useful in explaining various oxide behaviors. In this study, we aim to predict oxide acidity on the Smith scale using a machine learning approach. Previous attempts using a linear fit based on electronegativity showed a clear trend but lacked precision due to the simplicity of the model and the multi-valent nature of metal oxides. We propose a multi-parameter model incorporating four features: electronegativity, metal valence (raised to the power of 1/3), ionic radius, and dipole polarizability. A simple linear neural network outperformed a more complex 1D convolutional neural network, demonstrating superior accuracy and interpretability. Our model significantly improved predictive performance as compared to the single-parameter model. These results were validated through predictions testing data and unknow oxides acidity were predicted in this work.

https://doi.org/10.26434/chemrxiv-2024-kq9wl-v2

This study presents the development and evaluation of a novel GPT-like conditional molecule generator designed to optimize the synthesis of chemical compounds with desirable properties. The model incorporates six pivotal physicochemical properties as conditions: molecular weight, number of non-hydrogen atoms, ring count, hydrophobicity, quantitative estimation of drug-likeness (QED), and synthetic accessibility score (SAS). By integrating these specific attributes, the generator successfully produced a high-QED database, consisting of approximately 2 million molecules, all exhibiting a QED higher than 0.9. This achievement not only demonstrates the model's effectiveness in generating structurally diverse and potentially pharmacologically viable molecules but also underscores its utility in accelerating drug discovery processes.

https://doi.org/10.26434/chemrxiv-2024-tq75v

Integrated logic circuits using atomically thin, two-dimensional (2D) materials offer several potential advantages compared to established silicon technologies such as increased transistor density, circuit complexity, and lower energy dissipation leading to scaling benefits. In this article, a novel approach to achieve tunable doping in 2D semiconductors is explored to achieve complementary transistors and logic integration. By selectively transferring WSe2 onto hBN and SiO2 substrates, complementary transistor behavior (n- and p-type) was achieved using a UV light source and electrostatic activation. Furthermore, advanced characterization techniques, including high-resolution transmission electron microscopy (HRTEM) and Kelvin probe force microscopy (KPFM), provided insights into the chemical composition and surface potential changes after UV writing. Finally, a logic inverter was successfully implemented using selectively photo-induced doped WSe2 transistors, showcasing the potential for practical logic applications. This innovative method opens new avenues for designing energy-efficient and reconfigurable 2D semiconductor circuits, addressing key challenges in modern electronics.

https://doi.org/10.1002/smsc.202300319

This study employs novel growth methodologies and surface sensitization with metal nanoparticles to enhance and manipulate gas sensing behavior of two-dimensional (2D)SnS film. Growth of SnS films is optimized by varying substrate temperature and laser pulses during pulsed laser deposition (PLD). Thereafter, palladium (Pd), gold (Au), and silver (Ag) nanoparticles are decorated on as-grown film using gas-phase synthesis techniques. X-ray diffraction (XRD), Raman spectroscopy, and Field-emission scanning electron microscopy (FESEM) elucidate the growth evolution of SnS and the effect of nanoparticle decoration. X-ray photoelectron spectroscopy (XPS) analyses the chemical state and composition. Pristine SnS, Ag, and Au decorated SnS films are sensitive and selective toward NO2 at room temperature (RT). Ag nanoparticle increases the response of pristine SnS from 48 to 138% toward 2 ppm NO2, which indicates electronic and chemical sensitization effect of Ag. Pd decoration on SnS tunes its selectivity toward H2 gas with a response of 55% toward 70 ppm H2 and limit of detection (LOD) < 1 ppm. In situ Kelvin probe force microscopy (KPFM) maps the work function changes, revealing catalytic effect of Ag toward NO2 in Ag-decorated SnS and direct charge transfer between Pd and SnS during H2 exposure in Pd-decorated SnS.

https://doi.org/10.1002/smll.202307037

This paper presents the results of research into improving the ionic conductivity of Molten Carbonate Fuel Cell by modifying the matrix material. So far, we have succeeded in using materials such as YSZ and SDC, but we are now trying to use powders based on Ba Na and TiO2. These materials are characterized by their oxygen ion conductivity at elevated temperatures. A matrix of these materials was produced and used to build MCFCs. Based on the experiments carried out and the mathematical model of the fuel cell, the contribution of the oxygen ion conductivity to the total ionic conductivity was determined.

https://doi.org/10.1016/j.ijhydene.2023.06.116

Composite ceramic membranes based on the ionic conducting Tm-stabilized δ-Bi₂O₃ (BTM) and the electronic conducting (La_0.8Sr_0.2)_0.99MnO_3-δ (LSM) exhibit among the highest oxygen flux values reported for Bi₂O₃-based membranes. Here, we use pulse-response isotope exchange (PIE) and oxygen flux measurements to elaborate on limiting factors for the oxygen permeation in BTM - 40-70 vol% LSM composites. Once both phases percolate, between 30 and 50 vol% BTM, the flux is essentially independent of the BTM/LSM volume ratio. The oxygen permeability is under mixed diffusion- and surface control, gradually becoming more bulk-limited with increasing temperature. The oxygen exchange coefficients of BTM-LSM are significantly higher than its constituent phases, revealing that a cooperative surface exchange mechanism enhances the kinetics. Some of the Tm was substituted with Pr to introduce electronic conductivity in BTM. (Bi_0.8Tm_0.15Pr_0.05)₂O_3-δ (BTP) exhibits higher surface exchange coefficients compared to BTM, but the oxygen flux remains one order of magnitude lower than that of percolating BTM-LSM composites.

https://doi.org/10.1016/j.memsci.2022.120875

Dual-phase CO₂ separation membrane consisting of molten carbonates confined in a solid matrix can separate CO₂ at high temperatures. The contact angle of molten carbonates to different oxides that can potentially serve as membrane supports was screened between 450 and 650 °C. These oxides have different electrical transport properties, including oxide ion, mixed, and electronic conducting. The contact angles vary between 80° and 10° for different materials. Asymmetric membranes were fabricated using wettable oxide ion conductors BTM and CGO (Bi_0.8Tm_0.2O_1.5 and Ce_0.8Gd_0.2O_2-δ) infiltrated with molten carbonates supported by the most "non-wetting" oxide BPR (Bi_0.8Pr_0.2O_1.5) selected in the contact angle screening. The membranes show CO₂ flux in the range of 0.035–0.35 ml/min cm² at temperatures from 500 to 650 °C. Compared to a symmetric membrane with similar total membrane thickness, the asymmetric architecture significantly reduces the effective membrane thickness and increases CO₂ flux. After the CO₂ flux measurements, the membrane was examined with SEM and EDS mapping, showing that the molten carbonates were mainly confined within the top membrane and sealing area without penetrating the support layer.

https://doi.org/10.1016/j.memsci.2022.120447

Among the many extraordinary qualities of graphene, its thermoelectric properties have attracted significant interest, for example, in active cooling applications. Here, we report on the thermoelectric transport properties of centimeter-sized monolayer CVD graphene, electrostatically controlled by a high-capacity ionic gel. The power factor reaches 7 and 5.4 mW m^–1 K^–2 for hole and electron conduction, respectively, similar to earlier reports obtained for microdevices despite our devices being over 2 orders of magnitude larger. On the basis of these results, we propose nonvolatile ferroelectric polarization as a scalable technology for graphene-based thermoelectric applications.

https://doi.org/10.1021/acsaelm.1c00995

In the present paper, we demonstrate how modifications of the microstructure and the chemical composition can influence the electrochemical behavior of cathodes for molten carbonate fuel cells (MCFCs). Based on our experience, we designed new MCFC cathode microstructures combining layers made of porous silver, nickel oxide or nickel foam to overcome common issues with the internal resistance of the cell. The microstructures of the standard NiO cathode and manufactured cathodes were extensively investigated using scanning electron microscopy (SEM) and porosity measurements. The electrochemical behavior and overall cell performance were examined by means of electrochemical impedance spectroscopy and single-cell tests in operation conditions. The results show that a porous silver layer tape cast onto standard NiO cathode and nickel foam used as a support layer for tape cast NiO porous layer substantially decrease resistance components representing charge transfer and mass transport phenomena, respectively. Therefore, it is beneficial to combine them into a three-layer cathode since it facilitates separation of predominant physio-chemical processes of gas and ions transport in respective layers ensuring high efficiency. The superiority of the three-layer cathode has been proven by low impedance and high power density as compared to standard NiO cathode.

https://doi.org/10.1016/j.jpowsour.2021.229949

2D materials offer excellent possibilities for high performance gas detection due to their high surface-to-volume ratio, high surface activities, tunable electronic properties and dramatic change in resistivity upon molecular adsorption. This paper demonstrates a simple field effect transistor (FET) of molybdenum disulphide (MoS₂) fabricated on a hexagonal boron nitride (hBN) substrate that can detect NO_x down to concentrations of 6 ppb and possibly far below at room temperature (RT) with a systematic optimization of the device design and fabrication parameters as well as the device operating conditions. The effects of the substrate, number of MoS₂ layers, channel layout and biasing conditions on the response of MoS₂ FETs to NOx were investigated, providing directions for maximizing the sensitivity. This work also sheds light the issues of recovery and stability and present a methodology for calibration of the sensors which is critical for repeatable and reliable measurements.

https://doi.org/10.1016/j.sna.2020.112247

This paper presents progress in development of microstructure in MCFC electrodes. Within these studies the influence of microstructure parameters of materials, such as porosity and pore size distribution on the fuel cell power density is analyzed using pure nickel. The results indicate that the optimal range of porosity for MCFC electrodes can be related with specific surface area, which reveals maximum for volume fraction of pores being 55–60%. The porosity of the cathode should be 5–10% higher due to in situ oxidation taking place during the startup procedure. Pore size distribution, PSD, was found to be especially important in MCFC, where liquid electrolyte infiltrates electrodes by capillary action. Through the application of specific porogens, multimodal PSD can be obtained, which significantly enhances reference cell power density. Optimization of basic microstructure parameters informed the design of a new concept MCFC cathode incorporating bi-layered materials, where each layer is appointed a different role. The application of commercial nickel foam as the gas side layer of the cathode increased power density and reduced the brittleness of the element, which is of key importance from the technological point of view.

https://doi.org/10.1016/j.ijhydene.2019.12.038

This paper demonstrates the benefits of using a metallic foam support within molten carbonate fuel cell (MCFC) cathodes. A state-of-the-art fabrication process based on tape casting has been developed to produce microporous electrodes with a nickel foam scaffold. Surfactant was added to control the depth to which the slurry infiltrated the foam. New cathodes were used as an alternative to the traditional cathode in the single cell assembly and were tested for power density. Mechanical properties were compared with the current state-of-the-art. The results show that the use of metallic foams for high temperature fuel cell electrodes is beneficial from the technological point of view, especially in larger scale production. It was also found that the resultant continuous metallic structure of the microporous electrodes delivered a slight enhancement to fuel cell power density.

https://doi.org/10.1016/j.matdes.2020.108864

Within this study, a layered cathode for use in a Molten Carbonate Fuel Cell (MCFC) has been developed. The substrate layer and reference MCFC cathode made of porous nickel was covered by a porous silver film with defined porosity and pore size. Both layers were fabricated using the tape casting method and further fired in a reductive atmosphere. The new cathode was assembled with other reference cell components to form a single MCFC, which was subjected to performance and durability tests. Scanning electron microscopy was used to analyze the microstructure of the materials before and after tests. The reference cathode was also studied for the comparison. The results show that the porous silver layer was able to enhance the electron transport between the cathode and current collector. It was also found that oxygen reduction is enhanced due to the presence of silver in the gas supply. As a result, the power density of the cell was increased by 50%. On the other hand, due to the separation from electrolyte by the NiO layer, no significant degradation of the silver layer, identified by SEM or electrochemical tests, was found after 1000 h.

https://doi.org/10.1016/j.ijhydene.2020.05.112

Asymmetric tubular ceramic–ceramic (cercer) membranes based on La27W3.5Mo1.5O55.5−δ-La0.87Sr0.13CrO3−δ were fabricated by a two-step firing method making use of water-based extrusion and dip-coating. The performance of the membranes was characterized by measuring the hydrogen permeation flux and water splitting with dry and wet sweep gases, respectively. To explore the limiting factors for hydrogen and oxygen transport in the asymmetric membrane architecture, the effect of different gas flows and switching the feed and sweep sides of the membrane on the apparent hydrogen permeability was investigated. A dusty gas model was used to simulate the gas gradient inside the porous support, which was combined with Wagner diffusion calculations of the dense membrane layer to assess the overall transport across the asymmetric membrane. In addition, the stability of the membrane was investigated by means of flux measurements over a period of 400 h.

https://doi.org/10.3390/membranes9100126

In a solid-liquid dual-phase CO2 separation membrane, the native ions in the molten alkali carbonate, including carbonate anions and metal cations can transport CO2 in a process that is charge-compensated by electronic species (electrons or holes), oxide ions, or hydroxide ions, depending on materials and conditions. This strongly affects the design of experiments for assessing the performance of these membranes, and further determines the routes for integration of these membranes in industrial applications. Here we report how dissolved oxides in the liquid carbonate improve the CO2 flux of the membrane due to an enhanced charge-compensating oxygen ion transport. A qualitative understanding of the magnitude and role of oxide ion conductivity in the molten phase and in the solid support as a function of the temperature is provided. Employing a solid matrix of ceria, and dissolving CsVO3 and MoO3 oxides in the molten carbonate phase led to an almost doubled CO2 flux at 550 °C under dry ambient conditions. When the sweep gas contained 2.5% H2O, the CO2 flux was increased further due to formation of hydroxide ions in the molten carbonate acting as charge compensating species. Also, as a consequence of permeation controlled by ions in the liquid phase, the CO2 flux increased with the pore volume of the solid matrix.

https://doi.org/10.1016/j.seppur.2018.11.090

Ceramic oxygen separation membranes can be utilized to reduce CO2 emissions in fossil fuel power generation cycles based on oxy-fuel combustion. State-of-the-art oxygen permeable membranes based on Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) offer high oxygen permeability but suffer from long-term instability, especially in the presence of CO2. In this work, we present a novel ceramic composite membrane consisting of 60 vol% (Bi0.8Tm0.2)2O3−δ (BTM) and 40 vol% (La0.8Sr0.2)0.99MnO3−δ (LSM), which shows not only comparable oxygen permeability to that of BSCF but also outstanding long-term stability. At 900 °C, oxygen fluxes of 1.01 mL min−1 cm−2 and 1.33 mL min−1 cm−2 were obtained for membranes with thicknesses of 1.35 mm and 0.75 mm, respectively. Moreover, significant oxygen fluxes were obtained at temperatures down to 600 °C. A stable operation of the membrane was demonstrated with insignificant changes in the oxygen flux at 750 °C for approx. one month and at 700 °C with 50% CO2 as the sweep gas for more than two weeks.

https://doi.org/10.1039/C8CC10077B

Membranes for selective carbon dioxide permeation are likely to be important devices in future separation processes relevant to the energy industry. Here we review the current state of research into a particular class of carbon dioxide permeable membrane: the supported molten-salt membrane. Such membranes rely upon ionic transport pathways through a molten salt with or without electronic and ionic transport contributions from the inorganic support. This variety of transport pathways allows a considerable degree of flexibility in membrane design. The use of molten salts permits high temperature operation and produces highly permeable membranes with theoretically infinite selectivity. Here we review work on materials selection and properties, likely permeation mechanisms and the role and control of membrane microstructure. We review results from permeation experiments and discuss the importance of materials compatibility and the role of interfacial processes in membrane degradation. We finish with comments on prospects for scale-up and commercialisation.

https://doi.org/10.1039/C9TA01979K

Mixed conducting dense ceramic gas separation membranes can be used in air separation for oxy-fuel and pre-combustion processes in CO2 capture schemes for emission-free power plants and chemical industries. Such membranes operate at high temperatures, and the energy penalty associated with heating the membranes with external electrical heaters or burners via the feed or sweep gas can be significantly reduced by adopting direct ohmic heating of the membrane. We demonstrate that tubular asymmetric gas separation membranes of La2NiO4+δ and La0.87Sr0.13CrO3-δ can be heated to temperatures in excess of 800 °C by passing current through them, and that such ohmically heated tubular membranes can be operated in an oxygen potential gradient to selectively separate oxygen from a feed gas mixture. We highlight the associated challenges with heat transport and thermal gradients and undertake numerical simulations to investigate the effect of materials properties on heating power and heat distribution in the tubes.

https://doi.org/10.1016/j.memsci.2018.07.070

Novel asymmetric hydrogen permeable membranes consist of a dense ceramic–ceramic (cercer) composite layer of La0.87Sr0.13CrO3-δ and La27W3.5Mo1.5O55.5-δ deposited on a tubular porous support of the latter composition. The membranes were produced by extrusion and dip-coating with various thermal cycles required for adjusting the thermal shrinkage of the different layers and obtaining gas tight membrane layers. The produced asymmetric membranes have a dense cercer layer thicknesses ranging from 25 to 50 μm on supports exhibiting a porosity of up to 40 vol%. The effect of processing parameters, such as volume of pore former, coating steps, sintering temperature and soaking time on the microstructure of the membranes is discussed to highlight critical steps in the manufacturing protocol. Hydrogen fluxes were measured as a function of temperature with both wet and dry Ar sweep gas. Results are discussed with respect to membrane architectures and materials properties.

https://doi.org/10.1016/j.jeurceramsoc.2017.11.015

Three architectures of asymmetric tubular oxygen transport membranes (OTM) based on CaTi0.6Fe0.15Mn0.25O3-δ were fabricated with various thicknesses of the tubular porous supports and the dense membrane layers. This was achieved by a two-step firing method combining water based extrusion and dip-coating. The oxygen flux of the tubular membranes was characterized as a function of temperature and oxygen partial pressure on both feed and sweep sides for the different architectures. The flux exhibits different functional dependencies with respect to the oxygen partial pressure gradient and the membrane architecture. Numerical simulations using a Dusty-gas model were conducted to evaluate the effect of the porous support microstructure and thickness on oxygen partial pressure gradient inside the porous media. Results from this work were used to establish dependency of the flux with respect to bulk transport properties of the material, surface kinetics and architecture of the porous support. Furthermore, long-term stability of the produced tubular asymmetric membrane operated in CO2-containing atmospheres was assessed over half a year. The membrane exhibited a stable oxygen flux without showing significant flux degradation.

https://doi.org/10.1016/j.memsci.2017.11.042

Ceramic–ceramic composite (cercer) membranes of (Mo-doped) lanthanum tungstate, La27(W,Mo)5O55.5−δ, and lanthanum chromite, La0.87Sr0.13CrO3−δ, have recently been shown to exhibit H2 permeabilities among state-of-the-art. The present work deals with the long-term stability of these cercer membranes in line with concern of flux degradation and phase instability observed in previous studies. The H2 permeability of disc shaped membranes with varying La/W ratio in the lanthanum tungstate phase (5.35≤La/W≤5.50) was measured at 900 and 1000 °C with a feed gas containing 49% H2 and 2.5% H2O for up to 1500 h. It was observed that the H2 permeability decreased by a factor of up to 5.3 over 1500 h at 1000 °C. Post-characterization of the membranes and similarly annealed samples was performed by SEM, STEM and XRD, and segregation of La2O3 was observed. The decrease in H2 permeability was ascribed to the compositional instability of the cation-disordered lanthanum tungstate under the measurement conditions. Equilibration of the La/W ratio by segregation of La2O3 leads to a lower ionic conductivity according to the materials inherent defect chemistry. Partial decomposition and reduction of the lanthanum tungstate phase, presumably to metallic tungsten, was also observed after exposure to nominally dry hydrogen.

https://doi.org/10.1016/j.memsci.2015.12.054

Dense symmetric membranes of CaTi0.85−xFe0.15MnxO3−δ (x = 0.1, 0.15, 0.25, 0.4) are investigated in order to determine the optimal Mn dopant content with respect to highest O2 flux. O2 permeation measurements are performed as function of temperature between 700°C–1000°C and as function of the feed side ranging between 0.01 and 1 bar. X‐ray photoelectron spectroscopy is utilized to elucidate the charge state of Mn, and synchrotron radiation X‐ray powder diffraction (SR‐XPD) is employed to investigate the structure symmetry and cell volume of the perovskite phase at temperatures up to 800°C. The highest O2 permeability is found for x = 0.25 over the whole temperature and ranges, followed by x = 0.4 above 850°C. The O2 permeability for x = 0.25 reaches 0.01 mL(STP) min−1 cm−1 at 925°C with 0.21 bar feed side and Ar sweep gas. X‐ray photoelectron spectroscopy indicates that the charge state of Mn changes from approx. +3 to +4 when x > 0.1, which implies that Mn mainly improves electronic conductivity for x > 0.1. The cell volume is found to decrease linearly with Mn content, which coincides with an increase in the activation energy of O2 permeability. These results are consistent with the interpretation of the temperature and pO2 dependency of O2 permeation. The sintering behavior and thermal expansion properties are investigated by dilatometry, which show improved sinterability with increasing Mn content and that the thermal expansion coefficient decreases from 12.4 to 11.9 × 10−6 K−1 for x = 0 and x = 0.25, respectively.

https://doi.org/10.1111/jace.14022

Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3−δ and compared to CaTi0.6Fe0.15Mn0.25O3−δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 °C and as function of feed side from 10−2 to 1 bar, and at high pressures up to 4 bar with a of 3.36 bar. The O2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.9×10−3 mL min−1 cm−1 at 900 °C for a feed side of 0.21 bar. The O2 permeability of CaTi0.6Fe0.15Mn0.25O3−δ shows little variation with increased feed side pressures and reaches 1.5×10−2 mL min−1 cm−1 at 900 °C for a feed side of 3.36 bar. This is approximately 1.5 times higher than the O2 permeability with a feed side of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3−δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 °C; the results indicate a high creep resistance for this class of materials. The measured O2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability.

https://doi.org/10.1016/j.memsci.2015.10.016

Dual phase membranes are highly CO2-selective membranes with an operating temperature above 400 °C. The focus of this work is to quantify the potential of dual phase membranes in pre- and post-combustion CO2 capture processes. The process evaluations show that the dual phase membranes integrated with an NGCC power plant for CO2 capture are not competitive with the MEA process for post-combustion capture. However, dual phase membrane concepts outperform the reference Selexol technology for pre-combustion CO2 capture in an IGCC process. The two processes evaluated in this work, post-combustion NGCC and pre-combustion IGCC, represent extremes in CO2 partial pressure fed to the separation unit. Based on the evaluations it is expected that dual phase membranes could be competitive for post-combustion capture from a pulverized coal fired power plant (PCC) and pre-combustion capture from an Integrated Reforming Cycle (IRCC).

https://doi.org/10.1039/C6FD00038J

Dense dual-phase membranes consisting of a molten carbonate embedded in the interconnected pores of a ceramic framework are considered for potential application in CO2 separation at elevated temperatures utilising ambipolar conduction of carbonate ions and other charge carriers in the molten or solid phase. We have developed an experimental setup for determining transport numbers of various species in the molten carbonate phase by means of electromotive force (emf) measurements. Transport numbers of native and foreign ions are characterized for the eutectic mixture of Li-Na-K carbonate, which is embedded in a porous alumina matrix with Pt or lithiated NiO electrodes. The voltage is measured under activity gradients of CO2, O2, or H2O at 550°C. Electrochemical impedance spectra are collected during emf measurements. The true transport numbers of both native and foreign ions are calculated by taking into account the electrode polarization. The corrected transport numbers of native (carbonate and alkali metal) ions are close to unity at 550°C based on the emf under a gradient. Minor transport of oxide ions and hydroxide ions in the molten carbonate is observed under a gradient and gradient, respectively. This offers an alternative understanding and operation of molten carbonate dual-phase membranes.

https://doi.org/10.1149/2.0121510jes

Steam dissolving into molten carbonates through the formation of hydroxide ions could contribute to the permeation of CO2 in dual-phase membranes under certain conditions. In this work, ceria (CeO2) supported dual-phase membranes was fabricated and the effect of steam on the transport properties has been investigated by means of flux measurements. The results show an approximate 30% increase of the CO2 flux when 2.5% steam is introduced to the feed side, while an approximate 250–300% increase of the CO2 flux is observed when introducing the same amount of steam to the sweep side. These phenomena and transport mechanisms are explained by the theory of ambipolar permeation of CO2 via various combinations of charged species.

https://doi.org/10.1016/j.memsci.2015.02.029

Oxygen permeation measurements are performed on dense samples of CaTi0.85Fe0.15O3−δ, CaTi0.75Fe0.15Mg0.05O3−δ and CaTi0.75Fe0.15Mn0.10O3−δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O2 permeability of CaTi1−xFexO3−δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 °C with feed side oxygen partial pressures between 0.01 and 1 bar. The O2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.2×10−3 ml min−1 cm−1 at 900 °C and 0.21 bar O2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x=0.2. While the O2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 °C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O2 permeability, i.e., oxygen vacancies and electronic charge carriers.

https://doi.org/10.1016/j.memsci.2015.02.036

Some compositions of ceramic hydrogen permeable membranes are promising for integration in high temperature processes such as steam methane reforming due to their high chemical stability in large chemical gradients and CO2 containing atmospheres. In the present work, we investigate the hydrogen permeability of densely sintered ceramic composites (cercer) of two mixed ionic-electronic conductors: La27W3.5Mo1.5O55.5−δ (LWM) containing 30, 40 and 50 wt% La0.87Sr0.13CrO3−δ (LSC). Hydrogen permeation was characterized as a function of temperature, feed side hydrogen partial pressure (0.1–0.9 bar) with wet and dry sweep gas. In order to assess potentially limiting surface kinetics, measurements were also carried out after applying a catalytic Pt-coating to the feed and sweep side surfaces. The apparent hydrogen permeability, with contribution from both H2 permeation and water splitting on the sweep side, was highest for LWM70-LSC30 with both wet and dry sweep gas. The Pt-coating further enhances the apparent H2 permeability, particularly at lower temperatures. The apparent H2 permeability at 700 °C in wet 50% H2 was 1.1×10−3 mL min−1 cm−1 with wet sweep gas, which is higher than for the pure LWM material. The present work demonstrates that designing dual-phase ceramic composites of mixed ionic-electronic conductors is a promising strategy for enhancing the ambipolar conductivity and gas permeability of dense ceramic membranes.

https://doi.org/10.1016/j.memsci.2015.01.027

Zr substituted acceptor doped SrCeO3 materials were synthesized by citric acid route and characterized by XRD and SEM. The hydrogen flux of the materials was measured as a function of temperature and hydrogen partial pressure on the feed side. The hydrogen permeability for SrCe0.7Zr0.25Tm0.05O3−δ and SrCe0.7Zr0.25Yb0.05O3−δ is similar under our measurement window and shows the same hydrogen partial pressure dependency. Under short circuit condition, the hydrogen permeability increased significantly by more than one order of magnitude indicating that the hydrogen transport is limited by electronic conduction under open circuit conditions. The observed data were discussed by applying defect chemistry and the conventional ambipolar transport theory. After the hydrogen permeation measurements, the indication of kinetic cation de-mixing was found by XRD analysis.

https://doi.org/10.1016/j.memsci.2014.09.027

Nominal Gd6WO12, Gd5.94Ca0.06WO12 − δ, Gd5.7Ca0.3WO12 − δ and Gd5.7WO12 − δ were synthesized by solid state reaction and wet chemistry methods. The structure and morphology of the materials were analyzed by XRD, SEM and TEM and the electrical conductivity was measured as a function of temperature in reducing and oxidizing atmospheres under wet and dry conditions. The total conductivity is essentially independent of composition above 700 °C. Below 700 °C, the conductivity of Ca-doped samples is higher than that of Gd6WO12 and Gd5.7WO12 − δ and increases with increasing doping concentration. The conductivity below 700 °C is also higher under wet compared to dry conditions and, moreover, the H–D isotope effect on the conductivity is significant. Based on this, and on conductivity characterization as a function of and , it was concluded that the materials are mixed ionic and electronic conductors where electrons and holes dominate at high temperatures and intermediate temperatures under sufficiently reducing and oxidizing conditions, respectively. Protons are the predominating ionic charge carriers below approximately 700 °C. The hydrogen flux through Gd5.7Ca0.3WO12 − δ was measured as a function of temperature under wet and dry sweep gas conditions, as well as with varying on the feed side, confirming the picture outlined by the conductivity measurements. A defect chemical model has been derived to which the conductivity data were fitted yielding thermodynamic and transport parameters describing the functional characteristics of the materials.

https://doi.org/10.1016/j.ssi.2014.04.012

The electrical conductivity of TiNb2O7 was characterized as a function of temperature, and . The total conductivity was independent of in the low oxygen partial pressure regime, while a dependency of was observed at higher oxygen partial pressures. The conductivity increased with increasing under oxidizing conditions below 700°C. Mixed electronic and protonic conduction was indicated by H/D isotope exchange and transport number measurements. A defect model based on interstitial type of hydration was established and fitted to the conductivity data allowing for determination of physicochemical parameters of hydration and electron migration.

https://doi.org/10.1111/jace.12558

Two composites consisting of the proton conducting Ca-doped LaNbO4 and electron conducting LaNb3O9 with, respectively 90 and 70 vol% LaNbO4 were prepared by spark plasma sintering. The amount of hydrogen produced at the sweep side was measured as a function of temperature and gradient under wet and dry sweep gas conditions. The hydrogen flux increases with increasing temperature and feed-side . The flux is significantly higher for the 70 vol% LaNbO4 composite than the 90 vol% LaNbO4 composite. Ambipolar conductivities calculated from the flux data showed the same dependence for both composites. The electrical conductivity of the 70 vol% LaNbO4 composite was characterized as a function of temperature under wet hydrogen. The microstructure and phase distribution of the two composites are analyzed and their transport properties with different flux limiting processes are discussed. An increased hydrogen production with wet compared to dry sweep gas is concluded to reflect water splitting due to transport of oxygen from the permeate to the feed side.

https://doi.org/10.1016/j.memsci.2012.06.008

The quest for novel solid electrolytes and mixed ionic electronic conductors is leading us to attempt aliovalent cation substitution of new classes of oxides, but in a number of cases such doping gives no or unexpected effects. A general feature of many such systems is that they are ternary or higher oxides in which two cations of different valence are site disordered, facilitated by similar size. Examples comprise TiNb2O7, TiP2O7, ZrP2O7 and Ba3La(PO4)3. Doping intended to create charge compensating mobile point defects may in these cases result only in shifting the ratio of the two disordered cations, as this may have a much lower energy cost. This is accompanied by the precipitation of a phase or domains rich in the expelled cation. Entropy and Gibbs energy changes by doping are calculated and compared for cation disordered and non-disordered systems for illustration.

https://doi.org/10.1016/j.ijhydene.2011.11.136

Undoped and 2 mol % Sc-, Y-, and La-doped have been synthesized by an aqueous phosphoric acid route and characterized by X-ray diffraction and scanning electron microscopy. The samples were fabricated by conventional and spark plasma sintering (SPS), and the electrical conductivity was examined from 500 to as a function of and or by impedance spectroscopy. The conductivity of the materials in was higher than in and dry atmospheres, indicating that proton conductivity is dominant, supported also by transport number measurements. The conductivity was independent of at all temperatures, showing that the conductivity is predominantly ionic (protonic) under oxidizing as well as more reducing conditions. The and temperature dependencies of the conductivity were modeled assuming that protons are charge-compensated by oxygen interstitials. The attempted acceptor doping does not influence the conductivity significantly. Less dense samples exhibit a conductivity contribution at low temperatures assigned to internal surfaces; this is avoided in the SPS samples.

https://doi.org/10.1149/1.3474942