Membranas de separación de gases basadas en conductores iónicos mixtos y sus aplicaciones en catálisis

La tesis está basada en el desarrollo de materiales sólidos conductores mixtos electrónicos-protónicos y para su aplicación en membranas de separación de hidrógeno a alta temperatura. A continuación se resumen brevemente las líneas principales de este trabajo. La separación de hidrógeno, a altas temperaturas (600-1000 ºC), es posible mediante la aplicación de membranas densas compuestas por conductores mixtos electrónicos-protónicos con selectividades teóricas del 100%. Para que un óxido sea conductor de protones debe cumplir las siguientes características: tener una estructura deficiente en oxígeno, absorber agua en su estructura y permitir el rápido transporte de los protones una vez se han incorporado en la estructura. Dentro de este tipo de materiales, la tesis se ha concentrado en el desarrollo y caracterización de compuestos basados en la familia de los zirconatos (BaZrO3) y más ampliamente en la familia de los wolframatos (Ln6WO12). Los objetivos marcados en el estudio de los compuestos pertenecientes a la familia de los zirconatos fueron: la mejora de la conductividad protónica y electrónica de los materiales, disminución de la resistencia del borde de grano (que limita la conductividad en este tipo de compuestos) y la mejora de la estabilidad en atmósferas con CO2. Esta mejora se llevó a cabo mediante la sustitución parcial de la posición B (Zr) con elementos de transición interna y externa. En el caso de los materiales basados en la familia de los wolframatos, la optimización de las propiedades electroquímicas y de estabilidad se llevó a cabo siguiendo diferentes estrategias: (a) Síntesis y desarrollo de los compuestos basados en el sistema Ln6WO12, donde Ln: La, Er, Eu y Nd, obteniéndose la fase pura a temperaturas inferiores a 1000 ºC con tamaños de partícula en el rango nanométrico. (b) Selección y estudio de los comEscolástico Rozalén, S. (2013). Membranas de separación de gases basadas en conductores iónicos mixtos y sus aplicaciones en catálisis [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/27219Palanci

Fluid Dynamic Modeling of Oxygen Permeation through Mixed Ionic-Electronic Conducting Membranes

[EN] The oxygen transport in a lab-scale experimental set-up for permeation testing of oxygen transport membranes has been modeled using computational fluid dynamics using Finite Element Analysis. The modeling considered gas hydrodynamics and oxygen diffusion in the gas phase and vacancy diffusion of oxygen in a perovskite disc-shaped membrane at 1273. K. In a first step, the model allowed obtaining the coefficient diffusion of oxygen. The parametric study showed that the set-up geometry and flow rate in the air compartment did not have major influence in the oxygen transport. However, very important polarization effects in the sweep-gas (argon) compartment were identified. The highest oxygen permeation flux and the lowest oxygen concentration on the membrane surface were obtained for the following conditions (in increasing order of importance): (1) a large gas inlet radius; (2) short gas inlet distance; and (3) a high gas flow rate. © 2011 Elsevier B.V.The Spanish Ministry for Science and Innovation (JAE-Pre 08-0058 grant and ENE2008-06302 project) and through FP7 NASA-OTM Project (NMP3-SL-2009-228701) is kindly acknowledged.Gozálvez-Zafrilla, JM.; Santafé Moros, MA.; Escolástico Rozalén, S.; Serra Alfaro, JM. (2011). Fluid Dynamic Modeling of Oxygen Permeation through Mixed Ionic-Electronic Conducting Membranes. Journal of Membrane Science. 378(1-2):290-300. https://doi.org/10.1016/j.memsci.2011.05.016S2903003781-

Chemical stability in H2S and creep characterization of the mixed protonic conductor Nd5.5WO11.25-d

[EN] The integration of hydrogen permeable membranes in catalytic membrane reactors for thermodynamically limited reactions such as steam methane reforming can improve the per-pass yield and simultaneously produce a high-purity H-2 stream. Mixed protonic electronic materials based membranes are potential candidates for these applications due to their elevated temperature operation, good stability and potentially low cost. However, a specific mechanical behavior and stability under harsh atmospheres is needed to guarantee sufficient lifetime in real-world processes. This work presents the mechanical characterization and a study of the chemical stability under H2S containing atmospheres for the compound Nd5.5WO11.(25-8) Mechanical characterization was performed by micro indentation and creep measurements in air. Chemical stability was evaluated by XRD and SEM and the effect of the H2S on the transport properties was evaluated by impedance spectroscopy. Under H2S atmospheres, the total conductivity increases at 600 degrees C and 700 degrees C. The conductivity increase is attributed to the incorporation of S2- ions in oxide-ion sublattice. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.This work was financially supported by the Spanish Government (ENE2014-57651-R and SEV-2012-0267 grants). Authors would like to thank to U. Gerhards, M. Fabuel, T. Osipova and Dr. Wesel for WDS and SEM analysis.Escolástico Rozalén, S.; Stournari, V.; Malzbender, J.; Haas-Santo, K.; Dittmeyer, R.; Serra Alfaro, JM. (2018). Chemical stability in H2S and creep characterization of the mixed protonic conductor Nd5.5WO11.25-d. International Journal of Hydrogen Energy. 43(17):8342-8354. https://doi.org/10.1016/j.ijhydene.2018.03.060S83428354431

Study of the Effect of Inorganic Particles on the Gas Transport Properties of Glassy Polyimides for Selective CO2 and H2O Separation

[EN] Three polyimides and six inorganic fillers in a form of nanometer-sized particles were studied as thick film solution cast mixed matrix membranes (MMMs) for the transport of CO2, CH4, and H2O. Gas transport properties and electron microscopy images indicate good polymer-filler compatibility for all membranes. The only filler type thatdemonstrated good distribution throughout the membrane thickness at 10 wt.% loading was BaCe0.2Zr0.7Y0.1O3 (BCZY). The influence of this filler on MMM gas transport properties was studied in detail for 6FDA-6FpDA in a filler content range from one to 20 wt.% and for Matrimid((R)) and P84((R)) at 10 wt.% loading. The most promising result was obtained for Matrimid((R))10 wt.% BCZY MMM, which showed improvement in CO2 and H2O permeabilities accompanied by increased CO2/CH4 selectivity and high water selective membrane at elevated temperatures without H2O/permanent gas selectivity loss.This work was financially supported by the Spanish Government (SEV-2016-0683, SVP-2014-068356, Project ENE2014-57651-R and IJCI-2016-28330 grants) and GeneralitatValenciana (PROMETEO/2018/006 grant) and Helmholtz-Zentrum Geesthacht (HZG) through the technology transfer project program and by the Helmholtz Association of German Research Centers through the Helmholtz Portfolio MEMBRAIN.Escorihuela-Roca, S.; Valero, L.; Tena, A.; Shishatskiy, S.; Escolástico Rozalén, S.; Brinkmann, T.; Serra Alfaro, JM. (2018). Study of the Effect of Inorganic Particles on the Gas Transport Properties of Glassy Polyimides for Selective CO2 and H2O Separation. 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Progress in Polymer Science, 39(5), 817-861. doi:10.1016/j.progpolymsci.2014.01.003Angelidaki, I., Treu, L., Tsapekos, P., Luo, G., Campanaro, S., Wenzel, H., & Kougias, P. G. (2018). Biogas upgrading and utilization: Current status and perspectives. Biotechnology Advances, 36(2), 452-466. doi:10.1016/j.biotechadv.2018.01.011Jeon, Y.-W., & Lee, D.-H. (2015). Gas Membranes for CO2/CH4 (Biogas) Separation: A Review. Environmental Engineering Science, 32(2), 71-85. doi:10.1089/ees.2014.0413Murali, R. S., Sankarshana, T., & Sridhar, S. (2013). Air Separation by Polymer-based Membrane Technology. Separation & Purification Reviews, 42(2), 130-186. doi:10.1080/15422119.2012.686000Kanehashi, S., Chen, G. Q., Ciddor, L., Chaffee, A., & Kentish, S. E. (2015). The impact of water vapor on CO2 separation performance of mixed matrix membranes. Journal of Membrane Science, 492, 471-477. doi:10.1016/j.memsci.2015.05.046Kreuer, K. D. (2003). Proton-Conducting Oxides. Annual Review of Materials Research, 33(1), 333-359. doi:10.1146/annurev.matsci.33.022802.091825HAUGSRUD, 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.2007.01.004Kim, S., Anselmi-Tamburini, U., Park, H. J., Martin, M., & Munir, Z. A. (2008). Unprecedented Room-Temperature Electrical Power Generation Using Nanoscale Fluorite-Structured Oxide Electrolytes. Advanced Materials, 20(3), 556-559. doi:10.1002/adma.200700715Fernández-Barquín, A., Casado-Coterillo, C., Palomino, M., Valencia, S., & Irabien, A. (2015). LTA/Poly(1-trimethylsilyl-1-propyne) Mixed-Matrix Membranes for High-Temperature CO2/N2Separation. Chemical Engineering & Technology, 38(4), 658-666. doi:10.1002/ceat.201400641Tena, A., Shishatskiy, S., Meis, D., Wind, J., Filiz, V., & Abetz, V. (2017). Influence of the Composition and Imidization Route on the Chain Packing and Gas Separation Properties of Fluorinated Copolyimides. Macromolecules, 50(15), 5839-5849. doi:10.1021/acs.macromol.7b01051Escorihuela, S., Tena, A., Shishatskiy, S., Escolástico, S., Brinkmann, T., Serra, J., & Abetz, V. (2018). Gas Separation Properties of Polyimide Thin Films on Ceramic Supports for High Temperature Applications. Membranes, 8(1), 16. doi:10.3390/membranes8010016Corma, A., Fornés, V., Guil, J. ., Pergher, S., Maesen, T. L. ., & Buglass, J. . (2000). Preparation, characterisation and catalytic activity of ITQ-2, a delaminated zeolite. Microporous and Mesoporous Materials, 38(2-3), 301-309. doi:10.1016/s1387-1811(00)00149-9Itoh, T., Mori, M., Inukai, M., Nitani, H., Yamamoto, T., Miyanaga, T., … Idemoto, Y. (2015). Effect of Annealing on Crystal and Local Structures of Doped Zirconia Using Experimental and Computational Methods. The Journal of Physical Chemistry C, 119(16), 8447-8458. doi:10.1021/jp5117118Vigneron, F., Sougi, M., Meriel, P., Herr, A., & Meyer, A. (1980). 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Science, 353(6299), 563-566. doi:10.1126/science.aag0274IZA Structure Comissionhttp://www.iza-structure.org/Lillepärg, J., Georgopanos, P., Emmler, T., & Shishatskiy, S. (2016). Effect of the reactive amino and glycidyl ether terminated polyethylene oxide additives on the gas transport properties of Pebax® bulk and thin film composite membranes. RSC Advances, 6(14), 11763-11772. doi:10.1039/c5ra22026bZhang, C., Dai, Y., Johnson, J. R., Karvan, O., & Koros, W. J. (2012). High performance ZIF-8/6FDA-DAM mixed matrix membrane for propylene/propane separations. Journal of Membrane Science, 389, 34-42. doi:10.1016/j.memsci.2011.10.003Fernández-Barquín, A., Casado-Coterillo, C., Palomino, M., Valencia, S., & Irabien, A. (2016). Permselectivity improvement in membranes for CO2/N2 separation. Separation and Purification Technology, 157, 102-111. doi:10.1016/j.seppur.2015.11.032Sabetghadam, A., Seoane, B., Keskin, D., Duim, N., Rodenas, T., Shahid, S., … Gascon, J. (2016). Metal Organic Framework Crystals in Mixed-Matrix Membranes: Impact of the Filler Morphology on the Gas Separation Performance. Advanced Functional Materials, 26(18), 3154-3163. doi:10.1002/adfm.201505352Khayet, M., & García-Payo, M. C. (2009). X-Ray diffraction study of polyethersulfone polymer, flat-sheet and hollow fibers prepared from the same under different gas-gaps. Desalination, 245(1-3), 494-500. doi:10.1016/j.desal.2009.02.013RECIO, R., PALACIO, L., PRADANOS, P., HERNANDEZ, A., LOZANO, A., MARCOS, A., … DEABAJO, J. (2007). Gas separation of 6FDA–6FpDA membranesEffect of the solvent on polymer surfaces and permselectivity. Journal of Membrane Science, 293(1-2), 22-28. doi:10.1016/j.memsci.2007.01.022Calle, M., Lozano, A. E., de Abajo, J., de la Campa, J. G., & Álvarez, C. (2010). Design of gas separation membranes derived of rigid aromatic polyimides. 1. Polymers from diamines containing di-tert-butyl side groups. 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Ultrahigh oxygen permeation flux through supported Ba0.5Sr0.5Co0.8Fe0.2O3-delta membranes

[EN] Oxygen transport membranes made of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) were manufactured by tape casting and co-firing. The disk-shaped membranes consisted of a top gastight layer (70 mu m thick) and a porous substrate (830 mu m thick) with 34% open porosity. The variation of the permeation operation conditions allowed (i) the identification of the different limitations steps in the permeation process, i.e., bulk oxygen ion diffusion, catalytic surface exchange and gas phase diffusion in the membrane compartments and porous substrate, and (ii) the ultimate optimization of the oxygen flux. The variables considered in the systematic permeation study included the inlet gas flow rate of the sweep and air feed, the temperature and the nature of the oxygen feed gas (air or pure oxygen). Moreover, the influence of the deposition of a catalytic activation layer (17 mu m thick) made of BSCF on top of the thin gastight layer was investigated. As a result of this parametric study, unpreceded oxygen flux values were achieved, i.e., a maximum flux of 67.7 ml(STP) min(-1) cm(-2) was obtained at 1000 degrees C using pure oxygen as the feed and argon as the sweep, while a flux of 12.2 ml(STP) min(-1) cm(-2) at 1000 degrees C was obtained when air was used as the feed. (C) 2011 Elsevier BM. All rights reserved.Financial support from the Spanish Ministry for Science and Innovation (Project ENE2008-06302 and FPI Grant JAE-Pre 08-0058), EU through FP7 NASA-OTM Project (NMP3-SL-2009-228701), and the Helmholtz Association of German Research Centres through the Helmholtz Alliance MEM-BRAIN (Initiative and Networking Fund) is kindly acknowledged. Mrs H. Burlet has contributed to this work with the careful revision of the English language.Baumann, S.; Serra Alfaro, JM.; Lobera González, MP.; Escolástico Rozalén, S.; Schulze-Kueppers, F.; Meulenberg, WA. (2011). Ultrahigh oxygen permeation flux through supported Ba0.5Sr0.5Co0.8Fe0.2O3-delta membranes. Journal of Membrane Science. 377(1-2):198-205. https://doi.org/10.1016/j.memsci.2011.04.050S1982053771-

Tuning Ternary Alloyed Nanoparticle Composition and Morphology by Exsolution in Double Perovskite Electrodes for CO2 Electrolysis

[EN] The intermittent nature of renewable energy resources makes imperative the development of efficient energy storage technologies. Solid oxide electrolysis cells (SOECs) are a promising alternative to energy conversion devices. SOECs can play an important role in the control of greenhouse gases by improving processes such as CO2 electrolysis. In order to enhance SOEC performance, exsolution of metal nanoparticles is emerging for the catalytic surface functionalization of electrodes, preventing sintering issues related to classical impregnation methods and enabling tailoring specific catalytic functions. In this work, a medium-entropy, double perovskite system SrxFeCo0.2Ni0.2Mn0.1Mo0.5O6-delta (x = 2.0, 1.9, and 1.8) was studied. We provide evidence of Fe-Co-Ni ternary alloyed exsolved nanoparticles, revealing that the alloy composition can be tuned by adjusting the reducing conditions. Exsolution temperature is critical for Fe content in nanoparticles, increasing as temperature increases, but Ni and Co are not significantly affected. Temperature adjustments allowed control over nanoparticle size and population, shrinking and growing, respectively, as temperature decreases. In contrast to what is usually described, A-site deficiency resulted in a decrease in nanoparticle exsolution because of NiO phase formation in x = 1.9 and 1.8, so that the x = 2.0 compound outperformed both non-stoichiometric materials, showing significantly larger populations. The three compounds exhibit important conductivity under both oxidizing and reducing atmospheres, which makes them promising electrodes. The Sr2FeCo0.2Ni0.2Mn0.1Mo0.5O6-delta material was integrated as a cathode in an asymmetrical electrolyte-supported cell, and its electrochemical performance under CO2 electrolysis conditions was studied. Our results showed a boost in electrocatalytic activity upon exsolution at 600 degrees C when compared to the fuel electrode without exsolved nanoparticles or exsolved at 800 degrees C, where the appearance of the secondary Ruddlesden-Popper phase was observed. Overall, here, we proved the possibility of obtaining ternary alloy exsolved nanoparticles and tuning their composition to enhance the performance of SOEC devices, paving the path for optimized metal-alloyed exsolved nanoparticle design, which might extend its applicability to other electrocatalytic processes in energy conversion and storage.The project that gave rise to these results received the support of a fellowship from Spanish Government (RTI2018-102161 grant) and "la Caixa" Foundation (ID 100010434 and grant LCF/BQ/PI20/11760015). Authors acknowledge the use of instrumentation and the technical advice provided by the National Facility ELECMI ICTS, node "Division de Microscopia Electronica"at Universidad de Cadiz. We thank the support of the Electronic Microscopy Service of the Universitat Politecnica de Valencia.López-García, A.; Almar-Liante, L.; Escolástico Rozalén, S.; Hungría, AB.; Carrillo-Del Teso, AJ.; Serra Alfaro, JM. (2022). Tuning Ternary Alloyed Nanoparticle Composition and Morphology by Exsolution in Double Perovskite Electrodes for CO2 Electrolysis. ACS Applied Energy Materials. 5(11):13269-13283. https://doi.org/10.1021/acsaem.2c01829132691328351

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

[EN] 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-delta 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-delta. 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 degrees C for the humidified sweep gas. The stability of BaZr0.8Y0.15M0.05O3-delta 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.Financial support by the Spanish Ministry for Economics and Competitiveness (JAE-Pre 08-0058, ENE2008-06302 and ENE2011-24761 grants) and the Helmholtz Association of German Research Centers through the Helmholtz Alliance MEM-BRAIN (Initiative and Networking Fund) is kindly acknowledged. Dr M. Ivanova thanks the Northern European Innovative Energy Research Program N-INNER (grant no. 09- 064274) and the German Federal Ministry of Education and Research (BMBF) for supporting the N-INNER Project ‘‘Novel High Temperature Proton and Mixed-Proton Electron Conductors for Fuel Cells and H2-separation membranes’’ (Contract 03SF0330).Escolástico Rozalén, S.; Ivanova, M.; Solis Díaz, C.; Roitsch, S.; Meulenberg, WA.; Serra Alfaro, JM. (2012). Improvement of transport properties and hydrogen permeation of chemically-stable proton conducting oxides bases on the system BaZr1-x-yYxMyO3-δ. RSC Advances. 2(11):4932-4943. https://doi.org/10.1039/C2RA20214JS4932494321

Gas Separation Properties of Polyimide Thin Films on Ceramic Supports for High Temperature Applications

[EN] Novel selective ceramic-supported thin polyimide films produced in a single dip coating step are proposed for membrane applications at elevated temperatures. Layers of the polyimides P84 (R), Matrimid 5218 (R), and 6FDA-6FpDA were successfully deposited onto porous alumina supports. In order to tackle the poor compatibility between ceramic support and polymer, and to get defect-free thin films, the effect of the viscosity of the polymer solution was studied, giving the entanglement concentration (C*) for each polymer. The C* values were 3.09 wt. % for the 6FDA-6FpDA, 3.52 wt. % for Matrimid (R), and 4.30 wt. % for P84 (R). A minimum polymer solution concentration necessary for defect-free film formation was found for each polymer, with the inverse order to the intrinsic viscosities (P84 (R) >= Matrimid (R) >> 6FDA-6FpDA). The effect of the temperature on the permeance of prepared membranes was studied for H-2, CH4, N-2, O-2, and CO2. As expected, activation energy of permeance for hydrogen was higher than for CO2, resulting in H-2/CO2 selectivity increase with temperature. More densely packed polymers lead to materials that are more selective at elevated temperatures.This work was financially supported by the Spanish Government through predoctoral training grants for Centres/units of Excellence "Severo Ochoa" (SEV-2016-0683), which gave S. Escorihuela the opportunity to undertake a research stay at Helmholtz-Zentrum Geesthacht (HZG), Spanish Ministry of Economy and Competitiveness (Project ENE2014-57651-R) and Helmholtz-Zentrum Geesthacht (HZG) through the technology transfer project program and by the Helmholtz Association of German Research Centers through the Helmholtz Portfolio MEMBRAIN. The authors thank M. Schieda and P. Merten for the support in the coating process and viscosity determination, and the microscopy service at Universitat Politecnica de Valencia (UPV) for the FE-SEM images.Escorihuela-Roca, S.; Tena, A.; Shishatskiy, S.; Escolástico Rozalén, S.; Brinkmann, T.; Serra Alfaro, JM.; Abetz, V. (2018). Gas Separation Properties of Polyimide Thin Films on Ceramic Supports for High Temperature Applications. Membranes. 8(1). https://doi.org/10.3390/membranes8010016S8

Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor

[EN] Nonoxidative methane dehydroaromatization (MDA: 6CH(4) C6H6 + 9H(2)) using shape-selective Mo/zeolite catalysts is a key technology for exploitation of stranded natural gas reserves by direct conversion into transportable liquids. However, this reaction faces two major issues: The one-pass conversion is limited by thermodynamics, and the catalyst deactivates quickly through kinetically favored formation of coke. We show that integration of an electrochemical BaZrO3-based membrane exhibiting both proton and oxide ion conductivity into an MDA reactor gives rise to high aromatic yields and improved catalyst stability. These effects originate from the simultaneous extraction of hydrogen and distributed injection of oxide ions along the reactor length. Further, we demonstrate that the electrochemical co-ionic membrane reactor enables high carbon efficiencies (up to 80%) that improve the technoeconomic process viability.This work was supported by the Research Council of Norway (grants 195912, 210418, 210765, and 219194) and the Spanish government (grants SEV-2012-0267 and ENE2014-57651). We thank the ALBA Synchrotron Light Laboratory for beam time provision. C.K. and P.K.V. have applied for a patent based on this work (PCT/EP2014/071697). Experimental data are available online at ftp://itqrepositorio.itq.upv.es/pub/.Hernández Morejudo, S.; Zanón González, R.; Escolástico Rozalén, S.; Yuste Tirados, I.; Malerod Fjeld, H.; Vestre, PK.; Coors, WG.... (2016). Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor. Science. 353(6299):563-566. https://doi.org/10.1126/science.aag0274S563566353629

Nd5.5W1xUxO11.25-delta system: Electrochemical characterization and hydrogen permeationstudy

This work presents the structural and electrochemical characterization of mixed conducting materials based on the system Nd5.5W1-xUxO11.25-delta where x = 0.1, 0.5 and 1. The evolution of the crystalline structure is studied as a function of the sintering temperature and the U content in the oxide lattice. The influence of hydration and pO(2) as well as the H/D isotopic effect are studied by DC-electrochemical measurements under reducing environments. Hydrogen permeation is carried out for Nd5.5WO11.25-delta and Nd5.5W0.9U0.O-1(11.25-delta) compounds in the range from 650 to 750 degrees C. Finally, stability of the developed materials at 800 degrees C is evaluated in contact with CO2-rich gas streams. This work completes previous reported studies On Ln(6-x)WO(12-y) based materials that show the possibility of engineering the conductivity properties of the Ln(6-x)WO(12-y) just by doping strategies. (C) 2015 Published by Elsevier B.VFinancial support by the Spanish Government (Grants ENE2011-24761, CSD-2009-0050 and SEV-2012-0267) and the Helmholtz Association of German Research Centers through the portfolio topic MEM-BRAIN is kindly acknowledged. The authors are indebted to M. Fabuel for sample preparation.Escolástico Rozalén, S.; Serra Alfaro, JM. (2015). Nd5.5W1xUxO11.25-delta system: Electrochemical characterization and hydrogen permeationstudy. Journal of Membrane Science. 489:112-118. doi:10.1016/j.memsci.2015.04.017S11211848