Surface kinetics and bulk transport in La2Ni0.5Cu0.5O4+δ membranes from conductivity relaxation

This work reports conductivity relaxation measurements on both uncoated (1.2 mm thick) and coated (2.0 mm thick) La2Ni0.5Cu0.5O4+δ membranes in the temperature range between 550-850 °C and oxygen partial pressures from 0.01 to 1.0 atm. The results show that surface kinetics has a significant effect on the relaxation profiles, especially at low temperatures and should not be neglected when extracting transport parameters. Oxygen chemical diffusion and surface exchange coefficients have been determined by transient conductivity with surface modification. Higher activation energy of surface exchange compared to bulk diffusion is observed in La2Ni0.5Cu0.5O4+δ, similar to that in La2NiO4+δ. Based on the oxygen partial pressure dependence of the surface exchange coefficient, it has been revealed that oxygen dissociative adsorption rate-limits the surface exchange.publishedVersio

Space–charge theory applied to the grain boundary impedance of proton conducting BaZr0.9Y0.1O3−δ.

The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr0.9Y0.1O3−δ as a function of pO2 and temperature. pO2-dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space–charge layers in the grain boundaries. A grain boundary core–space–charge layer model is therefore applied to interpret the data. Using a Mott–Schottky approximation, a Schottky barrier height of 0.5–0.6 V and an effective grain boundary width of 8–10 nm (=2× space–charge layer thickness) is obtained at 250 °C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space–charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra

Hydration in fluorite-related rare-earth cerates

Hydration enthalpy and water uptake in La2-xNdxCe2O7 series (x = 0.0, 0.5, 1.0 and 2.0) have been measured using combined thermogravimetry (TG) and differential scanning calorimetry (DSC), TG-DSC. The DSC data unambiguously yield standard molar hydration enthalpies of around -74 kJ/mol independent of water uptake. The TG results however needs interpretation according to a model, and it is clear that they cannot be fitted to a classical model of hydration of all disordered oxygen vacancies. Instead, the hydration appears to be limited to a small fraction of the free vacancies. Hydration further decreases as the Nd content (x) and long range order increases and regions of disorder decrease. We propose a new model explaining why hydration occurs only in a small fraction of the nominally free vacancies: The higher basicity of La/Nd compared to Ce enables hydration, and high coordination with La/Nd around OH is needed to stabilize the proton/hydroxide in order to obtain exothermic hydration. The statistical variation of coordination around oxygen sites in a disordered fluorite oxide creates a limited number of such oxide ions sites which results in limited hydration. It is expected that this new purely statistical approach to interactions in special cases of heavily defective compounds may apply to rationalize unexpected defect behavior also in other systems

Oxygen permeability and surface kinetics of composite oxygen transport membranes based on stabilized δ-Bi2O3

Composite ceramic membranes based on the ionic conducting Tm-stabilized δ-Bi2O3 (BTM) and the electronic conducting (La0.8Sr0.2)0.99MnO3-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. (Bi0.8Tm0.15Pr0.05)2O3-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.publishedVersio

High performance anodes with tailored catalytic properties for La5.6WO11.4-d; based proton conducting fuel cells

This work shows the development of anodes based Sr-doped LaCrO3 (LSC) for La5.6WO11.4-d;-based proton conducting fuel cells. The electrode was improved by considering the operation limitations of the LSC material, which is chemically compatible at high temperatures with La5.6WO11.4-d; in contrast with typically NiO-based composite anodes. Firstly, the synthesis of 10% Ce doped LSC material, its compatibility with LWO and superior conduction properties are presented. These properties make this composition suitable as anode material, although EIS analysis revealed that its operation is still limited by LF surface associated limiting processes. In order to improve the surface catalytic properties of the anode, Ni infiltration was conducted on sintered anode, resulting in the coating of the electrode surface with Ni nanoparticles and consequently in a further improvement of the anode performance. Specifically, the infiltrated anode with the highest Ni loading presents uniquely HF associated resistance and the Rp is 0.26 ohm cm2 at 750 ºC in wet H2.Balaguer Ramirez, M.; Solis Díaz, C.; Bozza, F.; Bonanos, N.; Serra Alfaro, JM. (2013). High performance anodes with tailored catalytic properties for La5.6WO11.4-d; based proton conducting fuel cells. Journal of Materials Chemistry. 1(9):3004-3007. doi:10.1039/c3ta01554hS3004300719Iwahara, H. (1995). Technological challenges in the application of proton conducting ceramics. Solid State Ionics, 77, 289-298. doi:10.1016/0167-2738(95)00051-7Fabbri, E., Bi, L., Pergolesi, D., & Traversa, E. (2011). High-performance composite cathodes with tailored mixed conductivity for intermediate temperature solid oxide fuel cells using proton conducting electrolytes. Energy & Environmental Science, 4(12), 4984. doi:10.1039/c1ee02361fHAUGSRUD, R. (2007). Defects and transport properties in Ln6WO12 (Ln=La, Nd, Gd, Er). Solid State Ionics, 178(7-10), 555-560. doi:10.1016/j.ssi.2007.01.004Haugsrud, R., & Kjølseth, C. (2008). Effects of protons and acceptor substitution on the electrical conductivity of La6WO12. Journal of Physics and Chemistry of Solids, 69(7), 1758-1765. doi:10.1016/j.jpcs.2008.01.002Solís, C., Escolastico, S., Haugsrud, R., & Serra, J. M. (2011). La5.5WO12-δ Characterization of Transport Properties under Oxidizing Conditions: A Conductivity Relaxation Study. The Journal of Physical Chemistry C, 115(22), 11124-11131. doi:10.1021/jp2015066Magrasó, A., Polfus, J. M., Frontera, C., Canales-Vázquez, J., Kalland, L.-E., Hervoches, C. H., … Haugsrud, R. (2012). Complete structural model for lanthanum tungstate: a chemically stable high temperature proton conductor by means of intrinsic defects. J. Mater. Chem., 22(5), 1762-1764. doi:10.1039/c2jm14981hSolís, C., Navarrete, L., Roitsch, S., & Serra, J. M. (2012). Electrochemical properties of composite fuel cell cathodes for La5.5WO12−δ proton conducting electrolytes. Journal of Materials Chemistry, 22(31), 16051. doi:10.1039/c2jm32061dQuarez, E., Kravchyk, K. V., & Joubert, O. (2012). Compatibility of proton conducting La6WO12 electrolyte with standard cathode materials. Solid State Ionics, 216, 19-24. doi:10.1016/j.ssi.2011.11.003Meschke, F., Dias, F. J., & Tietz, F. (2001). Journal of Materials Science, 36(23), 5719-5728. doi:10.1023/a:1012594406053Mohammed Hussain, A., Høgh, J. V. T., Jacobsen, T., & Bonanos, N. (2012). Nickel-ceria infiltrated Nb-doped SrTiO3 for low temperature SOFC anodes and analysis on gas diffusion impedance. International Journal of Hydrogen Energy, 37(5), 4309-4318. doi:10.1016/j.ijhydene.2011.11.087Serra, J. M., & Meulenberg, W. A. (2007). Thin-Film Proton BaZr0.85Y0.15O3Conducting Electrolytes: Toward an Intermediate-Temperature Solid Oxide Fuel Cell Alternative. Journal of the American Ceramic Society, 90(7), 2082-2089. doi:10.1111/j.1551-2916.2007.01677.xRicote, S., & Bonanos, N. (2010). Enhanced sintering and conductivity study of cobalt or nickel doped solid solution of barium cerate and zirconate. Solid State Ionics, 181(15-16), 694-700. doi:10.1016/j.ssi.2010.04.007Solís, C., Vert, V. B., Balaguer, M., Escolástico, S., Roitsch, S., & Serra, J. M. (2012). Mixed Proton-Electron Conducting Chromite Electrocatalysts as Anode Materials for LWO-Based Solid Oxide Fuel Cells. ChemSusChem, 5(11), 2155-2158. doi:10.1002/cssc.201200446Sfeir, J. (2003). LaCrO3-based anodes: stability considerations. Journal of Power Sources, 118(1-2), 276-285. doi:10.1016/s0378-7753(03)00099-5Caillot, T., Gauthier, G., Delichère, P., Cayron, C., & Cadete Santos Aires, F. J. (2012). Evidence of anti-coking behavior of La0.8Sr0.2Cr0.98Ru0.02O3 as potential anode material for Solid Oxide Fuel Cells directly fed under methane. Journal of Catalysis, 290, 158-164. doi:10.1016/j.jcat.2012.03.012Sauvet, A. (2004). Catalytic activity for steam methane reforming and physical characterisation of La1−xSrxCr1−yNiyO3−δ. Solid State Ionics, 167(1-2), 1-8. doi:10.1016/j.ssi.2003.11.021Zhu, W. Z., & Deevi, S. C. (2003). Development of interconnect materials for solid oxide fuel cells. Materials Science and Engineering: A, 348(1-2), 227-243. doi:10.1016/s0921-5093(02)00736-0Solís, C., & Serra, J. M. (2011). Adjusting the conduction properties of La0.995Ca0.005NbO4−δ by doping for proton conducting fuel cells electrode operation. Solid State Ionics, 190(1), 38-45. doi:10.1016/j.ssi.2011.03.008Dong, X., Ma, S., Huang, K., & Chen, F. (2012). La0.9−xCaxCe0.1CrO3−δ as potential anode materials for solid oxide fuel cells. International Journal of Hydrogen Energy, 37(14), 10866-10873. doi:10.1016/j.ijhydene.2012.04.112Adler, S. B. (1996). Electrode Kinetics of Porous Mixed-Conducting Oxygen Electrodes. Journal of The Electrochemical Society, 143(11), 3554. doi:10.1149/1.183725

Lanthanum tungstate membranes for H-2 extraction and CO2 utilization: Fabrication strategies based on sequential tape casting and plasma-spray physical vapor deposition

[EN] In the context of energy conversion efficiency and decreasing greenhouse gas emissions from power generation and energy-intensive industries, membrane technologies for H-2 extraction and CO2 capture and utilization become pronouncedly important. Mixed protonic-electronic conducting ceramic membranes are hence attractive for the pre-combustion integrated gasification combined cycle, specifically in the water gas shift and H-2 separation process, and also for designing catalytic membrane reactors. This work presents the fabrication, microstructure and functional properties of Lanthanum tungstates (La28-xW4+xO54+delta, LaWO) asymmetric membranes supported on porous ceramic and porous metallic substrates fabricated by means of the sequential tape casting route and plasma spray-physical vapor deposition (PS-PVD). Pure LaWO and W site substituted LaWO were employed as membrane materials due to the promising combination of properties: appreciable mixed protonic-electronic conductivity at intermediate temperatures and reducing atmospheres, good sinterability and noticeable chemical stability under harsh operating conditions. As substrate materials porous LaWO (non-substituted), MgO and Crofer22APU stainless steel were used to support various LaWO membrane layers. The effect of fabrication parameters and material combinations on the assemblies' microstructure, LaWO phase formation and gas tightness of the functional layers was explored along with the related fabrication challenges for shaping LaWO layers with sufficient quality for further practical application. The two different fabrication strategies used in the present work allow for preparing all-ceramic and ceramic-metallic assemblies with LaWO membrane layers with thicknesses between 25 and 60 mu m and H-2 flux of ca. 0.4 ml/min cm(2) measured at 825 degrees C in 50 vol% H-2 in He dry feed and humid Ar sweep configuration. Such a performance is an exceptional achievement for the LaWO based H-2 separation membranes and it is well comparable with the H-2 flux reported for other newly developed dual phase cer-cer and cer-met membranes.ProtOMem Project under the BMBF grant 03SF0537 is gratefully acknowledged. Furthermore, the authors thank Ralf Laufs for his assistance in operating the PS-PVD facility. Dr. A. Schwedt from the Central Facility for Electron Microscopy (Gemeinschaftslabor fur Elektronenmikroskopie GFE), RWTH Aachen University is acknowledged for performing the EBSD analysis on the PS-PVD samples.Ivanova, ME.; Deibert, W.; Marcano, D.; Escolástico Rozalén, S.; Mauer, G.; Meulenberg, WA.; Bram, M.... (2019). Lanthanum tungstate membranes for H-2 extraction and CO2 utilization: Fabrication strategies based on sequential tape casting and plasma-spray physical vapor deposition. Separation and Purification Technology. 219:100-112. https://doi.org/10.1016/j.seppur.2019.03.015S100112219A.A. Evers, The hydrogen society, More than just a vision? ISBN 978-3-937863-31-3, Hydrogeit Verlag, 16727 Oberkraemer, Germany, 2010.Deibert, W., Ivanova, M. E., Baumann, S., Guillon, O., & Meulenberg, W. A. (2017). Ion-conducting ceramic membrane reactors for high-temperature applications. Journal of Membrane Science, 543, 79-97. doi:10.1016/j.memsci.2017.08.016Arun C. Bose, Inorganic membranes for energy and environmental applications, Edt. A. C. Bose, ISBN: 978-0-387-34524-6, Springer Science+Business Media, LLC, 2009.M. Marrony, H. Matsumoto, N. Fukatsu, M. Stoukides, Typical applications of proton ceramic cells: a way to market? in: M. Marrony (ed.), Proton-conducting ceramics. From fundamentals to applied research, by Pan Stanford Publishing Pte. Ltd., ISBN 978-981-4613-84-2, 2016.Di Giorgio, P., & Desideri, U. (2016). Potential of Reversible Solid Oxide Cells as Electricity Storage System. Energies, 9(8), 662. doi:10.3390/en9080662A.L. Dicks, D.A.J. Rand, Fuel cell systems explained, ISBN: 9781118613528, John Wiley & Sons Ltd., 2018.Zheng, Y., Wang, J., Yu, B., Zhang, W., Chen, J., Qiao, J., & Zhang, J. (2017). A review of high temperature co-electrolysis of H2O and CO2to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology. 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Catalytic activation of ceramic H2 membranes for CMR processes

[EN] The application of catalytic membrane reactors can overcome some of the disadvantages that reactions for the direct conversion of methane to fuels and petrochemicals present. Hydrogen separation membranes can shift the reaction equilibrium by hydrogen removal, improving the separation, selectivity and yield of the reactions. La5.5WO11.25-delta/La0.87Sr0.13CrO3-delta (LWO/LSC) based membranes present a high H-2 flux within the temperature range where CMR can be applied. However, the catalytic activity of the material is very low and it has to be improved. This work presents the development of different catalytic layers based on LSC material and the study of their influence on the H-2 flux obtained by using 60/40-LWO/LSC membranes. Membranes coated with porous layer made of Ni-infiltrated La0.75Ce0.1Sr0.15CrO3-delta exhibited the best permeation flux but still 20% lower than the one reached using Pt layers. Stability of the catalytic layers is also evaluated under H2 permeation conditions and under high steam content methane. (C) 2016 Elsevier B.V. All rights reserved.Financial support by the Spanish Government (Grants ENE2014-57651-R, CSD-2009-0050 and SEV-2012-0267) and CoorsTek Membrane Sciences is kindly acknowledged. The authors are indebted to M. Fabuel for sample preparation. The support of the Servicio de Microscopia Electronica of the Universidad Politecnica de Valencia is also acknowledged.Escolástico Rozalén, S.; Kjolseth, C.; Serra Alfaro, JM. (2016). Catalytic activation of ceramic H2 membranes for CMR processes. Journal of Membrane Science. 517:57-63. doi:10.1016/j.memsci.2016.06.017S576351

Developing Android Applications with Arctis

The focus of this thesis is the design of Android applications from building blocks in Arctis. The Arctis tool is used for modeling applications with UML activities, which already can be deployed on the Java ME and Java SE platforms. State machines and a runtime support system are generated. Creation of a generator for Arctis, enabling deployment to the Android platform, is the key element in this work. The Android platform is presented using an example application. A discussion on challenges, solutions and architectures for the design and implementation of Android applications using Arctis is presented. Then, the example application is redesigned using Arctis building blocks and deployed as a Java project using the existing code generator for Java SE. The adaptations necessary for turning the Java project into a runnable Android project is studied in detail and serves as a basis for the development of our code generator, along with the discussion. After describing our code generator, several building blocks are designed for an Android building block library. Demonstration of the code generator and the building blocks are done by designing and deploying an Android application named emph{TwitterFromAndroid}

Sikre kort, kjærlighet og minner - En studie av seks personers verdifulle klær

Jeg ønsker å bidra til et skifte mot en mer miljøvennlig og etisk motebransje som tar hensyn til hvordan klær faktisk brukes og hvilken betydning de har for oss. Det er til nå utviklet lite kunnskap rundt klærs verdi. I denne masteroppgaven benyttes derfor kvalitative semistrukturerte forskningsintervjuer og garderobemetoden for å utforske seks personers tanker om hvilke klær i deres garderobe som har høyest verdi for dem og på hvilken måte. Garderobemetoden innebærer at det materielle tilkjennes en sentral posisjon i diskusjoner og i forskning på klær. Utvalget består av tre kvinner og tre menn mellom 22 og 26 år med ulik studie- og arbeidsbakgrunn. Studien viser at klær kan ha flere former for verdi, som her inndeles i syv kategorier og knyttes til 1) tid og minner, 2) komfort og velvære, 3) kjærlighet, 4) uovervinnelighet, 5) egen stil og personlig uttrykk, 6) nyhet og mote og 7) pengeverdi. Felles for de registrerte klærne er at de brukes mye. Slik blir de bærere av minner og kan hjelpe oss å huske det vi ellers kunne ha glemt. Klær kan gi en følelse av trygghet og selvstendighet, og samtidig representere bånd til andre mennesker. Her blir kjærlighet et sentralt tema. Videre kan klær være verdifulle ved å muliggjøre at ytre omstendigheter takles bedre ved å holde oss tørre og varme. Informantene forteller om en følelse av uovervinnelighet. Mange av plaggene som er registrert i studien er verdifulle for informantene av flere årsaker, og hører derfor hjemme i flere kategorier. De fem første kategoriene er de viktigste formene for verdi, samtidig som de to siste er tatt med fordi de har preget ideer om klær og verdi. Gjennomsnittsalder for de 63 registrerte plaggene er om lag 4 år, noe som kan tyde på at det nye ikke er det viktigste for informantene. Ved å undersøke menneskers forhold til klær og verdi, kan vi lære mer om oss selv og tingene vi omgir oss med. Dette er kunnskap som både etterlyses og som med fordel kan settes i sammenheng med blant annet design-praksis. Dette vil kunne bidra til at det produseres klær som har større potensiale for å bli likt, brukt og tatt vare på over lengre tid