Mariya Ivanova

Enhanced H2 Separation through Mixed Proton–Electron Conducting Membranes Based on La5.5W0.8M0.2O11.25−δ

La(5.5) WO11.25-δ is a proton-conducting oxide that shows high protonic conductivity, sufficient electronic conductivity, and stability in moist CO2 environments. However, the H2 flows achieved to date when using La(5.5) WO11.25-δ membranes are still below the threshold for practical application in industrial processes. With the aim of improving the H2 flow obtained with this material, La(5.5) WO11.25-δ was doped in the W position by using Re and Mo; the chosen stoichiometry was La(5.5) W0.8 M0.2 O11.25-δ . This work presents the electrochemical characterization of these two compounds under reducing conditions, the H2 separation properties, as well as the influence of the H2 concentration in the feed stream, degree of humidification, and operating temperature. Doping with both Re and Mo enabled the magnitude of H2 permeation to be enhanced, reaching unrivaled values of up to 0.095 mL min(-1) cm(-2) at 700 °C for a La(5.5) W0.8 Re0.2 O11.25-δ membrane (760 μm thick). The spent membranes were investigated by using XRD, SEM, and TEM on focused-ion beam lamellas. Furthermore, the stability in CO2 -rich and H2 S-containing atmospheres was evaluated, and the compounds were shown to be stable in the atmospheres studied.

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y

Mixed proton-electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic-electronic conductivity. Lanthanum tungstate La(6-x)WO(12-y) (with y = 1.5x + δ and x = 0.5-0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 °C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La(6-x)WO(12-y) and for all substituted La(6-x)WO(12-y) compounds was measured in the temperature range of 400-900 °C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 °C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.

Improvement of transport properties and hydrogen permeation of chemically-stable proton-conducting oxides based on the system BaZr1-x-yYxMyO3-δ

The structural and transport properties as well as the chemical stability of a series of proton-conducting oxides based on yttrium-doped barium zirconate were investigated. Specifically, Pr-, Fe- and Mn-doped BaZr1-x-yYxMyO3-δ compounds were prepared by solid state reaction. The compound exhibiting the highest total and protonic conductivity at elevated temperatures under reducing atmospheres was BaZr0.8Y0.15Mn0.05O3-δ. Temperature-programmed reduction experiments revealed a particular redox behavior related to the Mn-species under selected conditions. The hydrogen permeation was thoroughly studied as a function of the temperature, hydrogen concentration and the humidification degree in the sweep gas. Moreover, the transient processes induced by alternate step changes in the humidification degree of the sweep gas were analysed. The highest steady hydrogen evolution flow exceeded 0.03 ml min−1 cm−2 (0.9 mm-thick membrane) at 1000 °C for the humidified sweep gas. The stability of BaZr0.8Y0.15M0.05O3-δ under operation-relevant atmospheres (CO2-rich reducing atmosphere at high temperature) was tested using different techniques (X-ray diffraction (XRD), Raman, SEM, TEM and TG) and the results showed that this material is stable even when exposed to 115 ppm H2S.

Hydrogen separation through tailored dual phase membranes with nominal composition BaCe0.8Eu0.2O3-δ:Ce0.8Y0.2O2-δ at intermediate temperatures

Hydrogen permeation membranes are a key element in improving the energy conversion efficiency and decreasing the greenhouse gas emissions from energy generation. The scientific community faces the challenge of identifying and optimizing stable and effective ceramic materials for H2 separation membranes at elevated temperature (400–800 °C) for industrial separations and intensified catalytic reactors. As such, composite materials with nominal composition BaCe0.8Eu0.2O3-δ:Ce0.8Y0.2O2-δ revealed unprecedented H2 permeation levels of 0.4 to 0.61 mL·min−1·cm−2 at 700 °C measured on 500 μm-thick-specimen. A detailed structural and phase study revealed single phase perovskite and fluorite starting materials synthesized via the conventional ceramic route. Strong tendency of Eu to migrate from the perovskite to the fluorite phase was observed at sintering temperature, leading to significant Eu depletion of the proton conducing BaCe0.8Eu0.2O3-δ phase. Composite microstructure was examined prior and after a variety of functional tests, including electrical conductivity, H2-permeation and stability in CO2 containing atmospheres at elevated temperatures, revealing stable material without morphological and structural changes, with segregation-free interfaces and no further diffusive effects between the constituting phases. In this context, dual phase material based on BaCe0.8Eu0.2O3-δ:Ce0.8Y0.2O2-δ represents a very promising candidate for H2 separating membrane in energy- and environmentally-related applications.

Proton-conducting ceramic membranes for solid oxide fuel cells and hydrogen (H2) processing

Abstract: The reduction of greenhouse gas emissions such as CO2 is a major subject of current socioeconomic, environmental and political discussion. Of a special interest is electricity production using alternative energy sources, as well as reduction in the CO2 levels emitted by existing electricity generation power plants fuelled by coal or gas. This goal can be achieved by developing innovative technologies that make use of ceramic membranes. Proton-conducting ceramic membranes are relevant for a variety of energy-related applications and hence it is necessary to develop materials with improved functional properties and durability. The present chapter will review the fundamentals and relevant application-oriented properties of different proton-conducting ceramic materials for membrane manufacturing for a variety of applications.

Tailoring the structure and gas permeation properties of silica membranes via binary metal oxides doping

The sol–gel method was employed for the synthesis of binary X–Co (X: Mn, Cr) oxide-doped silica membranes with different X/Co molar ratios (X/Co: 0.1, 0.3, 0.9). Single-gas permeation tests were performed at 200 °C to determine the effect of the binary oxide composition on the amorphous silica network. The X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) indicated the presence of smaller MnxCo3−xO4 and CrxCo3−xO4 oxide nanocrystals in the silica matrix in addition to amorphous Co, Mn and Cr species. The H2/N2 permeance ratio decreased from (126.3 ± 9) to (10.7 ± 2) with an increase in X/Co molar ratio from 0.1 to 0.9 due to the formation of larger pores. However, the binary Co–X oxide-doped silica membrane with the lowest X content showed a H2/N2 permeance ratio, (126.3 ± 9), higher than that, (63.6 ± 6), of the single cobalt oxide silica membrane. Based on FTIR analysis, it was found that the densification of the membrane at low X content resulted from the formation of silica structures with narrowed siloxane rings. In contrast, the enlargement of siloxane rings due to favorable condensation reactions occurred at high X content.

Efficient intermediate-temperature steam electrolysis with Y:SrZrO3−SrCeO3 and Y:BaZrO3−BaCeO3 proton conducting perovskites

Ceramic proton conductors have the potential to become important components in future clean and efficient energy technologies. In this manuscript, barium cerium yttrium zirconate (Ba(Zr0.5Ce0.4)8/9Y0.2O2.9) and strontium cerium yttrium zirconate (SrZr0.5Ce0.4Y0.1O2.95), proton conducting perovskites were employed as solid oxide electrolysis cell (SOEC) electrolytes for hydrogen production via intermediate temperature steam electrolysis at 550 and 600 °C. Cathode-supported button cells examined for a 12 μm Ba(Zr0.5Ce0.4)8/9Y0.2O2.9 electrolyte, with Ni–SrZr0.5Ce0.4Y0.1O2.95 as the H2-electrode, and porous Ba0.5La0.5CoO3 as the anode reached current densities of 0.2 and 0.5 A cm−2 with applied voltage of 1.45 V, at 550 and 600 °C, respectively. Moreover, a hydrogen evolution rate of 127 μmol cm−2 per minute was achieved at 0.5 A cm−2, translating to a current efficiency of 82%. In addition, excellent cell performance was obtained using SrZr0.5Ce0.4Y0.1O2.95 as an electrolyte. Current densities of 0.2 and 0.5 A cm−2 were obtained at 600 °C with applied voltages of 1.28 and 1.63 V, achieving faradaic current efficiencies of 88 and 85%. The NiO–SrZr0.5Ce0.4Y0.1O3−δ composite cathode was more favorable for the densification of the supported Ba(Zr0.5Ce0.4)8/9Y0.2O2.9 electrolyte during sintering and could be promising for use as a cathode substrate in proton-conducting SOECs.

Influence of coal power plant exhaust gas on the structure and performance of ceramic nanostructured gas separation membranes

C wiring into nanoscale holes with high aspect ratio by electrodeposition is an important problem for 3-D integration in integrated circuit technology toward miniaturization of electronic devices. However, void and pinhole found in Cu wiring for the integration can cause trouble for miniature device. Cu electroplating method without void and pinhole is needed. We have proposed novel electroplating methods with supercritical carbon dioxide (sc-CO2) emulsion (EP-SCE). The electrochemical reaction is carried out in an emulsion of sc-CO2 in electrolyte with surfactants. Sc-CO2 has low viscosity and compatibility of hydrogen. Thus, this method is applicable in fine Cu wiring. The aim of this report is to examine Cu electrodeposition by using sc-CO2 emulsified electrolyte into nano-scale Cu wiring on the viewpoints of dissolution of Cu seed layer, gap-filling capability into nano-scale holes and contamination in the plated Cu. Moreover a continuous-flow reaction system is proposed and examined for filling of Cu into holes with 60 nm in diameter and aspect ratio of 2 and 5 by EP-SCE on a round-type large-area hole test element group with diameter of 300 mm, which has an integrated structure of Cu seed layer on TiN barrier layer sputtered on Si substrates.T spectroscopy has gained popularity as a promising non-invasive investigation tool in recent decades. In studies of solid-state pharmaceuticals, its usefulness is enhanced, since it enables one to distinguish diff erent polymorphic and pseudo-polymorphic forms. Terahertz absorption spectra are additive, meaning that the resulting spectrum of two or more compounds in the sample is an algebraic sum, in the linear region of the Beer’s law. For this reason, the evolving-in-time linear mixture of unknown pure components can be resolved using the blind source separation approach, where both spectral sources and their concentrations are to be estimated. Such an evolution occurs naturally in temperature-induced (pseudo) polymorphic transitions, i.e. dehydration, where the terahertz spectrum is the hydrate and dehydrates’s response with timevarying proportions. Conventionally, to estimate the kinetics of a reaction–an important physical-chemical parameter–the area of the unique spectral peak is integrated and normalized to evaluate the abundance, but a diffi culty of strongly overlapping peaks unable its application. To overcome this problem, we show, that by employing the blind source separation procedure, we can resolve a complex, multi-compound spectral mixture with signifi cant cross-bands, where the peak area method failed. We evaluate the performance of our approach in studies on dehydration of a well-known polycrystalline hydrate–α-D-glucose monohydrate. Seeing that the polymorphic transitions can completely change the properties of a pharmaceutical, our approach can fi nd application in a drug development process, where their careful characterization is of utmost importance.