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. Chemical Society Reviews, 46(5), 1427-1463. doi:10.1039/c6cs00403bGötz, M., Lefebvre, J., Mörs, F., McDaniel Koch, A., Graf, F., Bajohr, S., … Kolb, T. (2016). Renewable Power-to-Gas: A technological and economic review. Renewable Energy, 85, 1371-1390. doi:10.1016/j.renene.2015.07.066Woodhead publishing series in energy, Nr. 76, Membrane reactors for energy applications and basic chemical production, Edt. A. Basile, L. Di Paola, F.I. Hai, V. Piemonte, by Elsevier Ltd, ISBN 978-1-78242-223-5, 2015.Morejudo, S. H., Zanón, R., Escolástico, S., Yuste-Tirados, I., Malerød-Fjeld, H., Vestre, P. K., … Kjølseth, C. (2016). Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor. Science, 353(6299), 563-566. doi:10.1126/science.aag0274Malerød-Fjeld, H., Clark, D., Yuste-Tirados, I., Zanón, R., Catalán-Martinez, D., Beeaff, D., … Kjølseth, C. (2017). Thermo-electrochemical production of compressed hydrogen from methane with near-zero energy loss. Nature Energy, 2(12), 923-931. doi:10.1038/s41560-017-0029-4J. Franz, Energetic and economic analysis of CO2 retention in coal gasification power plants by means of polymer and ceramic membranes (dissertation, German), Ruhr-University Bochum, Germany, Shaker Verlag, 2013.Franz, J., & Scherer, V. (2011). Impact of ceramic membranes for CO2 separation on IGCC power plant performance. Energy Procedia, 4, 645-652. doi:10.1016/j.egypro.2011.01.100E. Forster, dissertation, Thermal stability of ceramic membranes and catalysts for H2-separation in CO-shift reactors, Energy and Environment Band, vol. 284, ISBN 978-3-95806-084-5, RUB 2015.Escolástico, S., Stournari, V., Malzbender, J., Haas-Santo, K., Dittmeyer, R., & Serra, J. M. (2018). Chemical stability in H2S and creep characterization of the mixed protonic conductor Nd5.5WO11.25-δ. International Journal of Hydrogen Energy, 43(17), 8342-8354. doi:10.1016/j.ijhydene.2018.03.060Mortalò, C., Rebollo, E., Escolástico, S., Deambrosis, S., Haas-Santo, K., Rancan, M., … Fabrizio, M. (2018). Enhanced sulfur tolerance of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ composite for hydrogen separation membranes. Journal of Membrane Science, 564, 123-132. doi:10.1016/j.memsci.2018.07.015Matsumoto, H., Shimura, T., Higuchi, T., Tanaka, H., Katahira, K., Otake, T., … Mizusaki, J. (2005). Protonic-Electronic Mixed Conduction and Hydrogen Permeation in BaCe[sub 0.9−x]Y[sub 0.1]Ru[sub x]O[sub 3−α]. Journal of The Electrochemical Society, 152(3), A488. doi:10.1149/1.1852442Cai, M., Liu, S., Efimov, K., Caro, J., Feldhoff, A., & Wang, H. (2009). Preparation and hydrogen permeation of BaCe0.95Nd0.05O3−δ membranes. Journal of Membrane Science, 343(1-2), 90-96. doi:10.1016/j.memsci.2009.07.011U. Balachandran, J. Guan, S.E. Dorris, A.C. Bose, G.J. Stiegel, in: Proceedings of the 5th ICIM, A-410, Nagoya, Japan, 1998.Qi, X. (2000). Electrical conduction and hydrogen permeation through mixed proton–electron conducting strontium cerate membranes. Solid State Ionics, 130(1-2), 149-156. doi:10.1016/s0167-2738(00)00281-2Zhan, S., Zhu, X., Ji, B., Wang, W., Zhang, X., Wang, J., … Lin, L. (2009). Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes. Journal of Membrane Science, 340(1-2), 241-248. doi:10.1016/j.memsci.2009.05.037Song, S. (2004). Hydrogen permeability of SrCe1−xMxO3−δ (x=0.05, M=Eu, Sm). Solid State Ionics, 167(1-2), 99-105. doi:10.1016/j.ssi.2003.12.010Wei, X., Kniep, J., & Lin, Y. S. (2009). Hydrogen permeation through terbium doped strontium cerate membranes enabled by presence of reducing gas in the downstream. Journal of Membrane Science, 345(1-2), 201-206. doi:10.1016/j.memsci.2009.08.041CHENG, S., GUPTA, V., & LIN, J. (2005). Synthesis and hydrogen permeation properties of asymmetric proton-conducting ceramic membranes. Solid State Ionics, 176(35-36), 2653-2662. doi:10.1016/j.ssi.2005.07.005Kniep, J., & Lin, Y. S. (2010). Effect of Zirconium Doping on Hydrogen Permeation through Strontium Cerate Membranes. Industrial & Engineering Chemistry Research, 49(6), 2768-2774. doi:10.1021/ie9015182LIANG, J., MAO, L., LI, L., & YUAN, W. (2010). Protonic and Electronic Conductivities and Hydrogen Permeation of SrCe0.95-xZrxTm0.05O3-δ(0≤x≤0.40) Membrane. Chinese Journal of Chemical Engineering, 18(3), 506-510. doi:10.1016/s1004-9541(10)60250-9Xing, W., Inge Dahl, P., Valland Roaas, L., Fontaine, M.-L., Larring, Y., Henriksen, P. P., & Bredesen, R. (2015). Hydrogen permeability of SrCe0.7Zr0.25Ln0.05O3− membranes (Ln=Tm and Yb). Journal of Membrane Science, 473, 327-332. doi:10.1016/j.memsci.2014.09.027Oh, T., Yoon, H., Li, J., & Wachsman, E. D. (2009). Hydrogen permeation through thin supported SrZr0.2Ce0.8−xEuxO3−δ membranes. Journal of Membrane Science, 345(1-2), 1-4. doi:10.1016/j.memsci.2009.08.031Hamakawa, S. (2002). Synthesis and hydrogen permeation properties of membranes based on dense SrCe0.95Yb0.05O3−α thin films. Solid State Ionics, 148(1-2), 71-81. doi:10.1016/s0167-2738(02)00047-4Escolástico, S., Ivanova, M., Solís, C., Roitsch, S., Meulenberg, W. A., & Serra, J. M. (2012). Improvement of transport properties and hydrogen permeation of chemically-stable proton-conducting oxides based on the system BaZr1-x-yYxMyO3-δ. RSC Advances, 2(11), 4932. doi:10.1039/c2ra20214jH. Matsumoto, T. Shimura, T. Higuchi, T. Otake, Y. Sasaki, K. Yashiro, A. Kaimai, T. Kawada, J. Mizusaki, Mixed protonic-electronic conduction properties of SrZr0.9−xY0.1RuxO3−δ, Electrochemistry, 72(12), 861–864.M.E. Ivanova, S. Escolático, M. Balaguer, J. Palisaitis, Y.J. Sohn, W.A. Meulenberg, O. Guillon, J. Mayer, J.M. Serra, Hydrogen separation through tailored dual phase membranes with nominal composition BaCe0.8Eu0.2O3−δ:Ce0.8Y0.2O2−δ at intermediate temperatures, Sci. Rep. 6 (2016) 34773–34787.S. Elangovan, B.G. Nair, T.A. Small, Ceramic mixed protonic-electronic conducting membranes for hydrogen separation (2007), US 7,258,820 B2, 1997.Rosensteel, W. A., Ricote, S., & Sullivan, N. P. (2016). Hydrogen permeation through dense BaCe 0.8 Y 0.2 O 3−δ – Ce 0.8 Y 0.2 O 2−δ composite-ceramic hydrogen separation membranes. International Journal of Hydrogen Energy, 41(4), 2598-2606. doi:10.1016/j.ijhydene.2015.11.053Rebollo, E., Mortalò, C., Escolástico, S., Boldrini, S., Barison, S., Serra, J. M., & Fabrizio, M. (2015). Exceptional hydrogen permeation of all-ceramic composite robust membranes based on BaCe0.65Zr0.20Y0.15O3−δ and Y- or Gd-doped ceria. Energy & Environmental Science, 8(12), 3675-3686. doi:10.1039/c5ee01793aMontaleone, D., Mercadelli, E., Escolástico, S., Gondolini, A., Serra, J. M., & Sanson, A. (2018). All-ceramic asymmetric membranes with superior hydrogen permeation. Journal of Materials Chemistry A, 6(32), 15718-15727. doi:10.1039/c8ta04764bKim, H., Kim, B., Lee, J., Ahn, K., Kim, H.-R., Yoon, K. J., … Lee, J.-H. (2014). Microstructural adjustment of Ni–BaCe0.9Y0.1O3−δ cermet membrane for improved hydrogen permeation. Ceramics International, 40(3), 4117-4126. doi:10.1016/j.ceramint.2013.08.066(Balu) Balachandran, U., Lee, T. H., Park, C. Y., Emerson, J. E., Picciolo, J. J., & Dorris, S. E. (2014). Dense cermet membranes for hydrogen separation. Separation and Purification Technology, 121, 54-59. doi:10.1016/j.seppur.2013.10.001Shimura, T. (2001). Proton conduction in non-perovskite-type oxides at elevated temperatures. Solid State Ionics, 143(1), 117-123. doi:10.1016/s0167-2738(01)00839-6HAUGSRUD, 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.2008.01.002Magrasó, 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/c2jm14981hSeeger, J., Ivanova, M. E., Meulenberg, W. A., Sebold, D., Stöver, D., Scherb, T., … Serra, J. M. (2013). Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y. Inorganic Chemistry, 52(18), 10375-10386. doi:10.1021/ic401104mScherb, T., Kimber, S. A. J., Stephan, C., Henry, P. F., Schumacher, G., Escolástico, S., … Banhart, J. (2016). Nanoscale order in the frustrated mixed conductor La5.6WO12−δ. Journal of Applied Crystallography, 49(3), 997-1008. doi:10.1107/s1600576716006415Van Holt, D., Forster, E., Ivanova, M. E., Meulenberg, W. A., Müller, M., Baumann, S., & Vaßen, R. (2014). Ceramic materials for H2 transport membranes applicable for gas separation under coal-gasification-related conditions. Journal of the European Ceramic Society, 34(10), 2381-2389. doi:10.1016/j.jeurceramsoc.2014.03.001Forster, E., van Holt, D., Ivanova, M. E., Baumann, S., Meulenberg, W. A., & Müller, M. (2016). Stability of ceramic materials for H2 transport membranes in gasification environment under the influence of gas contaminants. Journal of the European Ceramic Society, 36(14), 3457-3464. doi:10.1016/j.jeurceramsoc.2016.05.021Medvedev, D., Lyagaeva, J., Plaksin, S., Demin, A., & Tsiakaras, P. (2015). Sulfur and carbon tolerance of BaCeO3–BaZrO3 proton-conducting materials. Journal of Power Sources, 273, 716-723. doi:10.1016/j.jpowsour.2014.09.116Yang, L., Wang, S., Blinn, K., Liu, M., Liu, Z., Cheng, Z., & Liu, M. (2009). Enhanced Sulfur and Coking Tolerance of a Mixed Ion Conductor for SOFCs: BaZr 0.1 Ce 0.7 Y 0.2– x Yb x O 3–δ. Science, 326(5949), 126-129. doi:10.1126/science.1174811Duan, C., Kee, R. J., Zhu, H., Karakaya, C., Chen, Y., Ricote, S., … O’Hayre, R. (2018). Highly durable, coking and sulfur tolerant, fuel-flexible protonic ceramic fuel cells. Nature, 557(7704), 217-222. doi:10.1038/s41586-018-0082-6Kreuer, K. D. (2003). Proton-Conducting Oxides. Annual Review of Materials Research, 33(1), 333-359. doi:10.1146/annurev.matsci.33.022802.091825Fantin, A., Scherb, T., Seeger, J., Schumacher, G., Gerhards, U., Ivanova, M. E., … Banhart, J. (2016). Crystal structure of Re-substituted lanthanum tungstate La5.4W1−y Re y O12–δ (0 ≤ y ≤ 0.2) studied by neutron diffraction. Journal of Applied Crystallography, 49(5), 1544-1560. doi:10.1107/s1600576716011523Fantin, A., Scherb, T., Seeger, J., Schumacher, G., Gerhards, U., Ivanova, M. E., … Banhart, J. (2017). Relation between composition and vacant oxygen sites in the mixed ionic-electronic conductors La5.4W1−MO12− (M= Mo, Re; 0 ≤y≤ 0.2) and their mother compound La6−WO12− (0.4 ≤x≤ 0.8). Solid State Ionics, 306, 104-111. doi:10.1016/j.ssi.2017.04.005J.M. Serra, S. Escolástico, M.E. Ivanova, W.A. Meulenberg, H.-P. Buchkremer, D. Stöver, US2013-0216938-A1, 2013.Escolastico, S., Seeger, J., Roitsch, S., Ivanova, M., Meulenberg, W. A., & Serra, J. M. (2013). Enhanced H2Separation through Mixed Proton-Electron Conducting Membranes Based on La5.5W0.8M0.2O11.25−δ. ChemSusChem, 6(8), 1523-1532. doi:10.1002/cssc.201300091Gil, V., Gurauskis, J., Kjølseth, C., Wiik, K., & Einarsrud, M.-A. (2013). Hydrogen permeation in asymmetric La28 − xW4 + xO54 + 3x/2 membranes. International Journal of Hydrogen Energy, 38(7), 3087-3091. doi:10.1016/j.ijhydene.2012.12.105Palmqvist, L., Lindqvist, K., & Shaw, C. (2007). Porous Multilayer PZT Materials Made by Aqueous Tape Casting. Key Engineering Materials, 333, 215-218. doi:10.4028/www.scientific.net/kem.333.215Menzler, N. H., Malzbender, J., Schoderböck, P., Kauert, R., & Buchkremer, H. P. (2013). Sequential Tape Casting of Anode-Supported Solid Oxide Fuel Cells. Fuel Cells, 14(1), 96-106. doi:10.1002/fuce.201300153Schulze-Küppers, F., Baumann, S., Tietz, F., Bouwmeester, H. J. M., & Meulenberg, W. A. (2014). Towards the fabrication of La0.98−xSrxCo0.2Fe0.8O3−δ perovskite-type oxygen transport membranes. Journal of the European Ceramic Society, 34(15), 3741-3748. doi:10.1016/j.jeurceramsoc.2014.06.012Weirich, M., Gurauskis, J., Gil, V., Wiik, K., & Einarsrud, M.-A. (2012). Preparation of lanthanum tungstate membranes by tape casting technique. International Journal of Hydrogen Energy, 37(9), 8056-8061. doi:10.1016/j.ijhydene.2011.09.083Deibert, W., Schulze-Küppers, F., Forster, E., Ivanova, M. E., Müller, M., & Meulenberg, W. A. (2017). Stability and sintering of MgO as a substrate material for Lanthanum Tungstate membranes. Journal of the European Ceramic Society, 37(2), 671-677. doi:10.1016/j.jeurceramsoc.2016.09.033Escolástico, S., Vert, V. B., & Serra, J. M. (2009). Preparation and Characterization of Nanocrystalline Mixed Proton−Electronic Conducting Materials Based on the System Ln6WO12. Chemistry of Materials, 21(14), 3079-3089. doi:10.1021/cm900067kGil, V., Strøm, R. A., Groven, L. J., & Einarsrud, M.-A. (2012). La28−xW4+xO54+3x/2Powders Prepared by Spray Pyrolysis. Journal of the American Ceramic Society, 95(11), 3403-3407. doi:10.1111/j.1551-2916.2012.05377.xIvanova, M. E., Meulenberg, W. A., Palisaitis, J., Sebold, D., Solís, C., Ziegner, M., … Guillon, O. (2015). Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation. Journal of the European Ceramic Society, 35(4), 1239-1253. doi:10.1016/j.jeurceramsoc.2014.11.009Dittmeyer, R., Boeltken, T., Piermartini, P., Selinsek, M., Loewert, M., Dallmann, F., … Pfeifer, P. (2017). Micro and micro membrane reactors for advanced applications in chemical energy conversion. Current Opinion in Chemical Engineering, 17, 108-125. doi:10.1016/j.coche.2017.08.001Mauer, G., Vaßen, R., & Stöver, D. (2009). Thin and Dense Ceramic Coatings by Plasma Spraying at Very Low Pressure. Journal of Thermal Spray Technology, 19(1-2), 495-501. doi:10.1007/s11666-009-9416-0Bakan, E., & Vaßen, R. (2017). Ceramic Top Coats of Plasma-Sprayed Thermal Barrier Coatings: Materials, Processes, and Properties. Journal of Thermal Spray Technology, 26(6), 992-1010. doi:10.1007/s11666-017-0597-7Jarligo, M. O., Mauer, G., Bram, M., Baumann, S., & Vaßen, R. (2013). Plasma Spray Physical Vapor Deposition of La1−x Sr x Co y Fe1−y O3−δ Thin-Film Oxygen Transport Membrane on Porous Metallic Supports. Journal of Thermal Spray Technology, 23(1-2), 213-219. doi:10.1007/s11666-013-0004-yMarcano, D., Mauer, G., Sohn, Y. J., Vaßen, R., Garcia-Fayos, J., & Serra, J. M. (2016). Controlling the stress state of La1−Sr Co Fe1−O3− oxygen transport membranes on porous metallic supports deposited by plasma spray–physical vapor process. Journal of Membrane Science, 503, 1-7. doi:10.1016/j.memsci.2015.12.029Marcano, D., Mauer, G., Vaßen, R., & Weber, A. (2017). Manufacturing of high performance solid oxide fuel cells (SOFCs) with atmospheric plasma spraying (APS) and plasma spray-physical vapor deposition (PS-PVD). Surface and Coatings Technology, 318, 170-177. doi:10.1016/j.surfcoat.2016.10.088D. Marcano, G. Mauer, Y.J. Sohn, A. Schwedt, M. Bram, M.E. Ivanova, R. Vaßen, Plasma spray-physical vapor deposition of single phase lanthanum tungstate for hydrogen gas separation membranes, t.b. submitted (2018).Brunauer, S., Emmett, P. H., & Teller, E. (1938). Adsorption of Gases in Multimolecular Layers. Journal of the American Chemical Society, 60(2), 309-319. doi:10.1021/ja01269a023Ried, P., Lorenz, C., Brönstrup, A., Graule, T., Menzler, N. H., Sitte, W., & Holtappels, P. (2008). Processing of YSZ screen printing pastes and the characterization of the electrolyte layers for anode supported SOFC. Journal of the European Ceramic Society, 28(9), 1801-1808. doi:10.1016/j.jeurceramsoc.2007.11.018R. Mücke, Sintering of ZrO2-electrolytes in multilayered assemblies of SOFC, PhD Thesis, Ruhr-University, Bochum, 2007.Amsif, M., Magrasó, A., Marrero-López, D., Ruiz-Morales, J. C., Canales-Vázquez, J., & Núñez, P. (2012). Mo-Substituted Lanthanum Tungstate La28–yW4+yO54+δ: A Competitive Mixed Electron–Proton Conductor for Gas Separation Membrane Applications. Chemistry of Materials, 24(20), 3868-3877. doi:10.1021/cm301723aDANIELS, A. U., LOWRIE, R. C., GIBBY, R. L., & CUTLER, I. B. (1962). Observations on Normal Grain Growth of Magnesia and Calcia. Journal of the American Ceramic Society, 45(6), 282-285. doi:10.1111/j.1151-2916.1962.tb11145.

Mo-Substituted Lanthanum Tungstate La_{28–<i>y</i>}W_4+<i>y</i>O_54+δ: A Competitive Mixed Electron–Proton Conductor for Gas Separation Membrane Applications

Molybdenum substituted lanthanum tungstate, La_{28–<i>y</i>}(W_1–<i>x</i>Mo_<i>x</i>)_4+<i>y</i>O_54+δ (<i>x</i> = 0–1, <i>y</i> = 0.923), was investigated seeking for an enhancement of the n-type electronic conductivity for its use as a mixed electron–proton conductor in hydrogen gas separation membrane applications. The materials were synthesized by the freeze-drying precursor method, and they were single phase after firing between 1300 and 1500 °C for <i>x</i> ≤ 0.8. The crystal structure changed from cubic (<i>x</i> ≤ 0.4) to rhombohedral (<i>x</i> ≥ 0.6) with increasing the molybdenum content. Transmission electron microscopy (TEM) investigations revealed an ordering of the oxygen vacancies with increasing Mo-content, giving rise to superstructure domains. The dependency of the conductivity with the oxygen and water partial pressure showed that these materials are good mixed electron–proton conductors under wet reducing conditions for <i>x</i> ≤ 0.4. The conductivity of the materials with <i>x</i> ≥ 0.6 was dominated by electrons, and they are expected to be less chemically stable due to the lower redox stability of Mo⁶⁺. The total conductivities in humidified H₂ were 0.016 S/cm for <i>x</i> = 0.2 and 0.043 S/cm for <i>x</i> = 0.4 at 900 °C, and they were stable under these conditions for more than 60 h. The ambipolar proton–electron conductivity was estimated to be ∼1.6 × 10^–3 S/cm for <i>x</i> = 0.4 at temperatures as low as 600 °C, which makes this family of materials very interesting and competitive candidates for applications such as hydrogen gas separation membranes at lower temperatures than state-of-the-art materials

The lower exosphere of Titan: Energetic neutral atoms absorption and imaging

International audienceThe Saturn magnetosphere interacts with the Titan atmosphere through various mechanisms. One of them leads, by charge exchange reactions between the energetic Saturnian ions and the exospheric neutrals of Titan, to the production of energetic neutral atoms (ENAs). The Ion and Neutral Camera (INCA), one of the three sensors that comprise the Magnetosphere Imaging Instrument (MIMI) on the Cassini/Huygens mission to Saturn and Titan, images the ENA emissions in the Saturnian magnetosphere. This study focuses on the ENA imaging of Titan (for 20–50 keV H ENAs), with the example of the Ta Titan flyby (26 October 2004): our objective is to understand the positioning of the ENA halo observed around Titan. Thus we investigate the main ENA loss mechanisms, such as the finite gyroradii effects for the parent ions, or the charge stripping with exospheric neutrals. We show that multiple stripping and charge exchange reactions have to be taken into account to understand the ENA dynamics. The use of an analytical approach, taking into account these reactions, combined with a reprocessing of the INCA data, allows us to reproduce the ENA images of the Ta flyby and indicates a lower limit for ENA emission around the exobase. However, the dynamics of energetic particles through the Titan atmosphere remains complex, with an inconsistency between the ENA imaging at low and high altitudes

Hydrogen separation membranes based on dense ceramic composites in the La27W5O55.5–LaCrO3 system

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