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A detailed kinetic model for the reduction of oxygen on LSCF-GDC composite cathodes

Authors Alessandro Donazzi, Giulio Cordaro, Andrea Baricci, Zhao-Bin Ding, Matteo Maestri
Source
Electrochimica Acta
Time of Publication: 2020
Abstract A kinetic investigation of the Oxygen Reduction Reaction (ORR) is performed on LSCF-GDC composite cathodes (La0.4Sr0.6Co0.2Fe0.8O3-δ/Ce0.9Gd0.1O2-δ 50/50) spanning a wide range of operating conditions. EIS tests are carried out on symmetric cells between 700 C and 560 C at OCV, with O2/N2 mixtures at varying O2 molar fraction (5–21%). A dynamic, one-dimensional, physic model of the LSCF-GDC electrode is applied to rationalize the experimental results. The model simulates the spectra by solving mass and charge conservation equations, including terms for gas diffusion in the porous electrode and solid state transport in both the LSCF and the GDC lattice. A thermodynamically consistent, detailed kinetic scheme is applied to describe the ORR mechanism, which takes into account elementary steps of adsorption and desorption, first and second electronation at the gas/electrode interface, interfacial and lattice ion transfer. A full set of rate parameters (pre-exponential factors and activation energies) is derived by fitting to inhouse-measured impedance data, and validated against a well-established literature dataset. The sensitivity analysis supports the prevailing role of the TPB route over the 2 PB route, and highlights that the transfer of a single-charged oxygen adatom from the LSCF surface to the GDC lattice governs the ORR. The model clarifies the origin of distortions in measured impedance arcs, and captures the effect of O2 pressure on the observed electrochemical activity.
Remark https://doi.org/10.1016/j.electacta.2020.135620
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High performance and toxicity assessment of Ta3N5 nanotubes for photoelectrochemical water splitting

Authors Kaiqi Xu, Athanasios Chatzitakis, Sanne Risbakk, Mingyi Yang, Paul Hoff Backe, Mathieu Grandcolas, Magnar Bjrsb, Truls Norby
Source
Catalysis Today
Time of Publication: 2019
Abstract In this work, Co-based cocatalysts are electrodeposited on mesoporous Ta3N5 nanotubes. The electrodeposition time is varied and the optimized photoelectrode reaches a photocurrent density of 6.3 mA/cm2 at 1.23 V vs. SHE, under simulated solar illumination of 1 Sun, in 1 M NaOH. The best performing electrode, apart from the high photocurrent density, shows improved stability under intense photoelectrochemical water splitting conditions. The dual function of the cocatalyst to improve not only the photoelectrochemical performance, but also the stability, is highlighted. Moreover, we adopted a simple protocol to assess the toxicity of Co and Ta contained nanostructured materials (representing used photoelectrodes) employing the human cell line HeLa S3 as target cells.
Remark https://doi.org/10.1016/j.cattod.2019.12.031
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A CO2-Tolerant Perovskite Oxide with High Oxide Ion and Electronic Conductivity

Authors Ming Li, Hongjun Niu, John Druce, Helena Tllez, Tatsumi Ishihara, John A. Kilner, Hripsime Gasparyan, Michael J. Pitcher, Wen Xu, J. Felix Shin, Luke M. Daniels, Leanne A. H. Jones, Vin R. Dhanak, Dingyue Hu, Marco Zanella, John B. Claridge, and Matth
Source
Adv. Mater.
Time of Publication: 2019
Abstract Mixed ionic–electronic conductors (MIECs) that display high oxide ion con-ductivity (σo) and electronic conductivity (σe) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen sepa-ration membranes. Often MIECs exhibit sufficient σe but inadequate σo. It has been a long-standing challenge to develop MIECs with both high σo and stability under device operation conditions. For example, the well-known perovskite oxide Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) exhibits exceptional σo and electrocatalytic activity. The reactivity of BSCF with CO2, however, limits its use in practical applications. Here, the perovskite oxide Bi0.15Sr0.85Co0.8Fe0.2O3−δ (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σo among the highest for known MIECs, but also high CO2 tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO2. The combination of high oxide transport properties and CO2 tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications.
Remark DOI: 10.1002/adma.201905200
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Coexistence of three types of sodium motion in double molybdate Na9Sc(MoO4)6: 23Na and 45Sc NMR data and ab initio calculations

Authors Anton L. Buzlukov, Irina Yu. Arapova, Yana V. Baklanova, Nadezhda I. Medvedeva, Tatiana A. Denisova, Aleksandra A. Savina, Bogdan I. Lazoryak, Elena G. Khaikina and Michel Bardet
Source
Phys. Chem. Chem. Phys.
Volume: 22, Pages: 144-154
Time of Publication: 2020
Abstract The rechargeable Na-ion batteries attract much attention as an alternative to the widely used but expensive Li-ion batteries. The search for materials with high sodium diffusion is important for the development of solid state electrolytes. We present the results of experimental and ab initio studies of the Na-ion diffusion mechanism in Na9Sc(MoO4)6. The ion conductivity reaches the value of 3.6 10−2 S cm−1 at T ∼ 850 K. The 23Na and 45Sc NMR data reveal the coexistence of three different types of Na-ion motion in the temperature range from 300 to 750 K. They are activated at different temperatures and are characterized by substantially different dynamics parameters. These features are confirmed by ab initio calculations of activation barriers for sodium diffusion along various paths.
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Long-term (4 year) degradation behavior of coated stainless steel 441 used for solid oxide fuel cell interconnect applications

Authors Claudia Goebel, Robert Berger, Carlos Bernuy-Lopez, Jrgen Westlinder, Jan-Erik Svensson, Jan Froitzheim
Source
Journal of Power Sources
Time of Publication: 2019
Abstract The present work aims to investigate the long-term stability of Ce/Co coated AISI 441 used as an interconnect material in solid oxide fuel cells (SOFC). Being a commercially available alloy the use of AISI 441 would greatly reduce the cost of SOFCs in comparison to tailor-made interconnect materials such as Crofer 22 APU. To analyze the long-term stability Ce/Co coated AISI 441 is exposed in air at 800 C for up to 38 000 h. Mass gain values are recorded continuously. After 7 000, 23 000, and 35 000 h area specific resistance (ASR) measurements are performed, and cross-sections are prepared and analyzed using scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy. Cr-evaporation measurements are conducted on samples exposed for up to 38 000 h.
Keywords SOFC, Interconnect, Corrosion, Ce/Co coating, AISI 441, Long-term
Remark https://doi.org/10.1016/j.jpowsour.2019.227480
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Identification of barium-site substitution of BiFeO3–Bi0.5K0.5TiO3 multiferroic ceramics: X-ray absorption near edge spectroscopy

Authors Anurak Prasatkhetragarn, Jaru Jutimoosik, Pongsakorn Jantaratana, Pinit Kidkhunthod, Rattikorn Yimnirun, James Ren
Source
Radiation Physics and Chemistry
Volume: 170 Time of Publication: 2020
Abstract In this work, the effects of barium substitution on the local structure, dielectric and magnetic properties of the polycrystalline ceramics 0.6BiFeO3–0.4(Bi0.5K0.5)TiO3 (0.6BFO–0.4BKT) system was investigated. A solid-state reaction technique was used to synthesize the materials with barium (Ba) doping of 1, 3, 5, 7, and 10 mol%. XRD analysis reveals the coexistence between tetragonal and rhombohedral phases of single-phase perovskite in pure 0.6BFO–0.4BKT and the rhombohedral reach phase was found with increasing Ba content. XANES simulations indicate that the majority of Ba atoms occupy A-site in BKT lattice of Ba-doped 0.6BFO-0.4BKT, the oxidation state of Fe, Ti, and Ba ions are +3, +4 and+2, respectively. At 5 mol% of Ba doping content, the dielectric measurement shows the morphotropic phase boundary (MPB) and the maximum value of ferromagnetic characteristic were observed, indicating an optimum composition, properties and production conditions.
Keywords X-ray absorption near edge spectroscopy; Barium-doped; Multiferroic ceramics; XANES simulations
Remark https://doi.org/10.1016/j.radphyschem.2019.108621
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Tuning of Mg content to enhance the thermoelectric properties in binary Mg2+δ Si (δ = 0, 0.1, 0.15, 0.2)

Authors Priyadarshini Balasubramanian, Manjusha Battabyal, Dhruba Das, Arumugam Chandra Bose and Raghavan Gopalan
Source
Materials Research Express
Volume: 6 Time of Publication: 2019
Abstract We report the enhanced thermoelectric properties of binary Mg2Si by tuning the Mg content. Polycrystalline Mg2+δ Si (where δ is the excess Mg content in the starting composition of the samples and δ = 0, 0.1, 0.15, 0.2) samples were processed by solid-state synthesis route using ball milling followed by rapid spark plasma sintering in order to minimize the Mg loss during processing. Microstructural and x-ray diffraction analysis revealed that, Mg content (δ) of 0.1–0.15 is required to get the binary Mg2Si phase without any elemental Mg/Si phase. Hall effect measurement and Fourier Transform Infrared Spectroscopy analysis show that, the excess Mg content helps to enhance the carrier concentration and charge carrier effective mass due to the occupancy of Mg at the interstitial site in Mg2Si structure. The influence of Mg content on thermoelectric properties, viz., electrical resistivity, Seebeck coefficient and thermal conductivity is investigated from 300 K to 780 K. A marked enhancement in thermoelectric power factor (~1.6 mW m−2K−2) is obtained for Mg2.15Si sample at 780 K. The occupancy of excess Mg at interstitial sites reduces the lattice thermal conductivity by lowering lattice symmetry. A maximum figure of merit (ZT) ~ 0.39 0.03 at 780 K has been achieved in Mg2.15Si sample, the highest among that reported in n-type binary Mg2Si system. This suggests that excess Mg content in the starting composition of Mg2+δ Si helps in stabilizing the phase as well as improves the thermoelectric properties of the Mg2Si.
Remark https://doi.org/10.1088/2053-1591/ab58fb
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Exploring the Role of Manganese on Structural, Transport, and Electrochemical Properties of NASICON-Na3Fe2–yMny(PO4)3–Cathode Materials for Na-Ion Batteries

Authors Katarzyna Walczak, Bartłomiej Gędziorowski, Andrzej Kulka, Wojciech Zając, Magdalena Ziąbka, Rafał Idczak, Vinh Hung Tran and Janina Molenda
Source
ACS Applied Materials & Interfaces
Volume: 11, Issue: 46 Time of Publication: 2019
Abstract Given the extensive efforts focused on protecting the environment, eco-friendly cathode materials are a prerequisite for the development of Na-ion battery technology. Such materials should contain abundant and inexpensive elements. In the paper, we present NASICON-Na3Fe2–yMny(PO4)3 (y = 0, 0.1, 0.2, 0.3, and 0.4) cathode materials, which meet these requirements. Na3Fe2–yMny(PO4)3 compounds were prepared via a solid-state reaction at 600 C, which allowed to obtain powders with submicron particles. The presence of manganese in the iron sub-lattice inhibits phase transitions, which occurs at ∼95 and ∼145 C in Na3Fe2(PO4)3, changing the monoclinic structure to rhombohedral and affecting the structural and transport properties. The chemical stability of Na3Fe2–yMny(PO4)3 was thus higher than that of Na3Fe2(PO4)3, and it also exhibited enhanced structural, transport, and electrochemical properties. The observed correlation between the chemical composition and electrochemical properties proved the ability to precisely tune the crystal structure of NASICONs, allowing cathode materials with more desirable properties to be designed.
Keywords Na-ion batteries, XRD, crystal structure
Remark https://doi.org/10.1021/acsami.9b10184
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Intriguing electrochemistry in low-temperature single layer ceramic fuel cells based on CuFe2O4

Authors M. I. Asghar, X.Yao, S. Jouttijrvi, E. Hochreiner, R. Virta, P. D. Lund
Source
International Journal of Hydrogen Energy
Time of Publication: 2019
Abstract A composite of CuFe2O4 and Gd-Sm co-doped CeO2 is studied for a single layer ceramic fuel cell application. In order to optimize the cell performance, the effects of sintering temperatures (600 C, 700 C, 800 C, 900 C and 1000 C) were investigated for the fabrication of the cells. It was found that the cells sintered at 700 C outperformed other cells with a maximum peak power density of 344 mW/cm2 at 550 C. The electrochemical impedance spectroscopy analysis on the best cell revealed significant ohmic losses (0.399 Ω cm2) and polarization losses (0.174 Ω cm2) in the cell. The HR-TEM and SEM gave microstructural information of the cell. The HT-XRD spectra showed the crystal structures in different sintering temperatures. The cell performance was stable and the composite material did not degrade during an 8 h stability test under open-circuit condition. This study opens up new avenues for the exploration of this nanocomposite material for the low temperature single component ceramic fuel cell research.
Keywords Catalysis; Ceramic; Composite; Fuel cell; Single component
Remark https://doi.org/10.1016/j.ijhydene.2019.09.175
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Mn-rich SmBaCo0.5Mn1.5O5+δ double perovskite cathode material for SOFCs

Authors Anna Olszewska, Yang Zhang, Zhihong Du, Mateusz Marzec, Konrad Świerczek, Hailei Zhao, Bogdan Dabrowski
Source
International Journal of Hydrogen Energy
Volume: 44, Issue: 50 Time of Publication: 2019
Abstract SmBaCo0.5Mn1.5O5+δ oxide with Sm-Ba cation-ordered perovskite-type structure is synthesized and examined in relation to whole RBaCo0.5Mn1.5O5+δ series (R: selected rare earth elements). Presence of Sm and 3:1 ratio of Mn to Co allows to balance physicochemical properties of the composition, with moderate thermal expansion coefficient value of 18.70(1)10−6 K−1 in 300–900 C range, high concentration of disordered oxygen vacancies in 600–900 C range (δ = 0.16 at 900 C), and good transport properties with electrical conductivity reaching 33 S cm−1 at 900 C in air. Consequently, the compound enables to manufacture catalytically-active cathode, with good electrochemical performance measured for the electrolyte-supported laboratory-scale solid oxide fuel cell with Ni-Gd1.9Ce0.1O2-δ|La0.4Ce0.6O2-δ|La0.8Sr0.2Ga0.8Mg0.2O3-δ|SmBaCo0.5Mn1.5O5+δ configuration, for which 1060 mW cm−2 power density is observed at 900 C. Furthermore, the tested symmetrical SmBaCo0.5Mn1.5O5+δ|La0.8Sr0.2Ga0.8Mg0.2O3-δ|SmBaCo0.5Mn1.5O5+δ cell delivers 377 mW cm−2 power density at 850 C, which is a promising result.
Keywords Mn-rich layered perovskites; Physicochemical properties; Cathode materials; SOFC; Symmetrical SOFC
Remark https://doi.org/10.1016/j.ijhydene.2019.08.254
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Simultaneous CO2 and O2 separation coupled to oxy-dry reforming of CH4 by means of a ceramic-carbonate membrane reactor for in situ syngas production

Authors J. A. Fabin-Anguiano, C. G. Mendoza-Serrato, C. Gmez-Yez, B. Zeifert, Xiaoli Ma, J. Ortiz-Landeros
Source
Chemical Engineering Science
Volume: 210 Time of Publication: 2019
Abstract It is reported the use of a ceramic-carbonate membrane exhibiting CO2 and O2 permeation, coupled with the oxy-carbon dioxide reforming of methane to produce syngas in a membrane reactor arrangement. The studied membrane is made of a porous fluorite/perovskite mixed conducting ceramic infiltrated with molten carbonates. The CO2 and O2 gas mixture used to perform the oxy-dry reforming process is the membrane’s permeate, which reacts with CH4 supplied in the sweep gas with the assistance of a catalyst. The reactor converts from 74 to 99% of CH4 under the studied separation and reaction conditions. The total rate of syngas production reaches 6.25 mL∙min−1∙cm−2 at 875 C and a H2/CO ratio ranging from 2.1 to 1.3 between 800 and 875 C. A long-term test shows a stable performance for 300 h. This work suggests the feasibility of this capture-conversion concept for the valorization of CO2 by the efficient production of syngas.
Keywords Inorganic membrane; Gas permeation; Ceramic-carbonate membrane; Oxy-CO2 reforming of methane; Syngas production
Remark https://doi.org/10.1016/j.ces.2019.115250
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Factors Limiting the Apparent Hydrogen Flux in Asymmetric Tubular Cercer Membranes Based on La27W3.5Mo1.5O55.5 and La0.87Sr0.13CrO3

Authors Zuoan Li, Jonathan M. Polfus, Wen Xing, Christelle Denonville, Marie-Laure Fontaine and Rune Bredesen
Source
Membranes
Volume: 9 Time of Publication: 2019
Abstract Asymmetric tubular ceramic–ceramic (cercer) membranes based on La27W3.5Mo1.5O55.5-La0.87Sr0.13CrO3 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.
Keywords hydrogen permeation; water splitting; surface kinetics; asymmetric tubular membrane; lanthanum tungstate; lanthanum chromite
Remark doi:10.3390/membranes9100126
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Thermoelectric properties of A-site deficient La-doped SrTiO3 at 100–900 C under reducing conditions

Authors Sathya Prakash Singh, Nikola Kanas, Temesgen D.Desissa, Mats Johnsson, Mari-Ann Einarsrud, Truls Norby, Kjell Wiik
Source
Journal of the European Ceramic Society
Volume: 40, Issue: 2, Pages: 401-407
Time of Publication: 2020
Abstract Lanthanum doped strontium titanate is a potential n-type thermoelectric material at moderate and high temperatures. (La0.12Sr0.88)0.95TiO3 ceramics were prepared by two different routes, conventional sintering at 1500 C and spark plasma sintering at temperatures between 925 and 1200 C. Samples with grain size between 40 nm and 1.4 μm were prepared and characterized with respect to their thermoelectric transport properties at temperatures between 100 and 900 C under reducing conditions (H2/H2O-buffer mixtures). The thermal conductivity was significantly reduced with decreasing grain size reaching a value of 1.3 W m−1. K−1 at 600 C for grain size of 40 nm and porosity of 19%. Electrical conductivity increased with increasing grain size showing a maximum of 500 S cm−1 at 200 C for a grain size of 1.4 μm. The highest figure-of-merit (zT) was measured for samples with 1.4 μm average grain size reaching 0.2 at 500 C.
Remark https://doi.org/10.1016/j.jeurceramsoc.2019.09.024
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Ceria-Based Dual-Phase Membranes for High-Temperature Carbon Dioxide Separation: Effect of Iron Doping and Pore Generation with MgO Template

Authors Albert Gili , Benjamin Bischo, Ulla Simon, Franziska Schmidt, Delf Kober, Oliver Grke, Maged F. Bekheet and Aleksander Gurlo
Source
Membranes
Volume: 9, Issue: 9, Pages: 108
Time of Publication: 2019
Abstract Dual-phase membranes for high-temperature carbon dioxide separation have emerged as promising technology to mitigate anthropogenic greenhouse gases emissions, especially as a pre- and post-combustion separation technique in coal burning power plants. To implement these membranes industrially, the carbon dioxide permeability must be improved. In this study, Ce0.8Sm0.2O2−δ (SDC) and Ce0.8Sm0.19Fe0.01O2−δ (FSDC) ceramic powders were used to form the skeleton in dual-phase membranes. The use of MgO as an environmentally friendly pore generator allows control over the membrane porosity and microstructure in order to compare the effect of the membrane’s ceramic phase. The ceramic powders and the resulting membranes were characterized using ICP-OES, HSM, gravimetric analysis, SEM/EDX, and XRD, and the carbon dioxide flux density was quantified using a high-temperature membrane permeation setup. The carbon dioxide permeability slightly increases with the addition of iron in the FSDC membranes compared to the SDC membranes mainly due to the reported scavenging effect of iron with the siliceous impurities, with an additional potential contribution of an increased crystallite size due to viscous flow sintering. The increased permeability of the FSDC system and the proper microstructure control by MgO can be further extended to optimize carbon dioxide permeability in this membrane system.
Keywords samarium doped ceria; SDC; FSDC; CO2 separation membranes; scavenging effect of iron; permeability
Remark https://doi.org/10.3390/membranes9090108
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Microstructural and compositional optimization of La0.5Ba0.5CoO3−δ — BaZr1−zYzO3−δ (z=0,0.05 and 0.1) nanocomposite cathodes for protonic ceramic fuel cells

Authors Laura Rioja-Monllor, Carlos Bernuy-Lopez, Marie-Laure Fontaine,Tor Grande and Mari-Ann Einarsrud
Source
J. Phys.: Energy
Volume: 2 Time of Publication: 2019
Abstract Cathodes are one of the key components of protonic ceramic fuel cells (PCFCs) requiring further development to enhance the performance of PCFCs. This encompasses the optimization of material compositions and microstructures, as well as a further understanding of the electrode processes. Here, a compositional optimization of a La0.5Ba0.5CoO3−δ —BaZrO3-based nano-composite cathode prepared by exsolution of a single-phase material was performed by substituting 5 and 10 mol% Y at the B-site in the BaZrO3 phase. Electrodes with different microstructures were prepared by two different deposition methods, spray coating and screen printing, and by varying the firing temperature from 600C to 1100 C. Further, composite electrodes were prepared by directly coating and firing the single-phase materials on the dense electrolyte to prepare symmetric cells. A good adhesion of the cathode to the electrolyte was observed in all cases. In general, a more homogeneous microstructure was observed for the cathodes prepared by screen printing. The single step method encompassing exsolution of the single phase and firing of the symmetric cells yielded significant improvement in the cathode performance compared to the other routes. The best electrochemical performance was observed for La0.5Ba0.5CoO3−δ —BaZr0.9Y0.1O2.95 cathode with an area specific resistance of 4.02 Ω cm2 at 400 C and 0.21 Ω cm2 at 600 C in 3% moist synthetic air. These results are among the best reported for cathodes of PCFCs as will be discussed.
Keywords protonic ceramic fuel cells, cathode, exsolution, composites
Remark https://doi.org/10.1088/2515-7655/ab396c
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Conductivity studies on the substituted stannate pyrochlore system Gd2Sn2-x-yMxAyO7 (M= Ti and A = Ru; x = 0.5, 1.0 and 1.5; y = 0.2)

Authors N. Srinivasan, G.V.M. Kiruthika
Source
Solid State Sciences
Volume: 96 Time of Publication: 2019
Abstract Studies on the Gd2Sn2-x-yMxAyO7 system (M = Ti and A = Ru; x = 0.5, 1.0 and 1.5; y = 0.2) were carried out and the conductivity of the compounds was analyzed in air. All the substituted compounds form ordered pyrochlore structure. Enhanced conductivity properties were observed for the substituted compounds as compared to the Gd2Sn2O7 system. The more polarizable Ti–O and Ru–O bond and the smaller radius of Ti4+ and Ru4+ as compared to Sn4+ has a combined effect on the increased conductivity properties of the compounds. It is interesting to note that a striking enhancement of the total conductivity is observed for Gd2TiSn0.8Ru0.2O7 (~10−3 S/cm at 1000 C) as compared to Gd2TiSnO7 (10−6 S/cm at 1000 C). An optimized number of mobile charge carriers and activation energy for the oxide ionic conduction is found to influence the conductivity properties of the compounds.
Keywords Mixed ionic-electronic conductivity, Stannate pyrochlores, Oxide ion conductors
Remark https://doi.org/10.1016/j.solidstatesciences.2019.105957
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Fabrication and encapsulation of micro-SOFCs

Author Andrea Turchi
Source
Time of Publication: 2019
Remark Tesi di Laurea Magistrale
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Protonic conductivity and thermal properties of cross-linked PVA/TiO2 nanocomposite polymer membranes

Authors G.M. Aparicio, R.A. Vargas, P.R. Bueno
Source
Journal of Non-Crystalline Solids
Volume: 522 Time of Publication: 2019
Abstract Nanocomposite polymer membranes based on PVA/TiO2 were prepared by a solution casting method. Glutaraldehyde solution (GA) was used as linking agent to improve the chemical, thermal and physical properties of the membranes. The degree of cross-linking was varied by changing the reaction time. The phase behavior of the membranes was examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). High resolution SEM micrographs show that the TiO2 nanoparticles are homogeneously dispersed, whilst the PVA crosslinks with the inorganic phase and fill in the gap between the nanoparticles. The ionic conductivity measurements were studied by impedance spectroscopy in the radio frequency range between 5 kHz to 5 MHz. Proton conductivity increases by several orders of magnitude with increasing cross-linking reaction time, reaching a maximum of 0.016 Scm−1 at 130 C for the PVA/TiO2 composition of 1:12%, which was cross-linked for 42 h and then immersed in a 32 wt% KOH solution for 24 h. The ionic activation energy of the prepared membranes ranged from 0.038 KeV to 0.121 KeV. This result was carried out to obtain an estimation of the desorption time of water in the range from room temperature to the decomposition temperature around 500 C.
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Ultrahigh temperature platinum microheater encapsulated by reduced-TiO2 barrier layer

Authors Shunsuke Akasaka, Encho Boku, Yurina Amamoto, Hiroyuki Yuji, Isaku Kanno
Source
Sensors and Actuators A: Physical
Volume: 296, Pages: 286-291
Time of Publication: 2019
Abstract Thermal stability and adhesion of the Pt/barrier interface were investigated herein. Reduced-TiO2, or TiO2-δ, was found to offer stronger adhesion and greater thermal stability as a barrier layer for Pt than that of TiN and stoichiometric TiO2. It enables a long-term high-temperature operation. No voids or peeling was seen after annealing at a temperature of 700 C in a stacked layer of Pt/ TiO2-δ; whereas, voids and peeling inevitably appeared in Pt layers on TiN and TiO2, respectively. A microhotplate composed of a Pt/TiO2-δ microheater was confirmed to perform at 800 C at a heating power of 120 mW. The heating response time was below 20 ms between 150 C and 800 C. Ten million cycles of temperature modulation between room temperature and 550 C did not cause any performance deterioration.
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Synthesis and Study of (Sr,La)2FeCo0.5Mo0.5O6 − δ Oxides with Double Perovskite Structure

Authors M. M. Abdullaev, S.Ya. Istomin, A.V. Sobolev, I.A. Presnyakov, E.V. Antipov
Source
Russian Journal of Inorganic Chemistry
Volume: 64, Issue: 6, Pages: 696–704
Time of Publication: 2019
Abstract Complex oxides Sr2 − xLaxFeCo0.5Mo0.5O6 − δ, (x = 0.2, 0.4; δ ≈ 0.03–0.15) have been first synthesized by the sol-gel method. Their crystal structures have been refined by the Rietveld method; the refinement showed that the complex oxides have the structure of cubic double perovskite (a ≈ 2aper, space group Fm3̄m) with partial ordering of Fe(Co) and Mo in the B positions. Based on the 57Fe Mssbauer measurements, the average formal oxidation state of iron has been found to decrease from +3.20 (x = 0.0) to +3.04 (x = 0.4). Our study of the behavior of perovskites in a reducing Ar/H2 atmosphere (8%) revealed a decrease in the reduction resistance with decreasing La content (x = 0.4 → 0). The combination of the properties studied, namely chemical stability with respect to the reaction with Ce1 − xGdxO2 − x/2 and Zr1 − xYxO2 − x/2, high-temperature thermal expansion, and electrical conductivity in air and Ar/H2, shows that Sr1.6La0.4Fe-Co0.5Mo0.5O6 − δ (δ ≈ 0.03) perovskite is more attractive as an electrode material for medium-temperature symmetric solid oxide fuel cells than Sr2FeCo0.5Mo0.5O6 − δ.
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Influence of Lanthanum Doping on Structural and Electrical/Electrochemical Properties of Double Perovskite Sr2CoMoO6 as Anode Materials for Intermediate-Temperature Solid Oxide Fuel Cells

Authors Pravin Kumar, Paramananda Jena, P. K. Patro, R. K. Lenka, A. S. K. Sinha, Prabhakar Singh, Rajendra Kumar Singh
Source
ACS Appl. Mater. Interfaces
Volume: 11, Issue: 27, Pages: 24659-24667
Time of Publication: 2019
Abstract Lanthanum (La3+)-doped double perovskites Sr2CoMoO6 (Sr2–xLaxCoMoO6, 0.00 ≤ x ≤ 0.03) were synthesized via the citrate–nitrate autocombustion route. The Reitveld refinement analysis of X-ray diffraction reveals the tetragonal symmetry as the main phase with space group I4/m and also confirms the presence of some peaks corresponding to extra phase SrMoO4. The SEM micrograph images reflect that grains are in irregular shape and sizes for all samples. Average grain size gradually decreases with the increase of the SrMoO4 phase. The X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of mixed valence states of Mo5+/Mo6+, Co2+/Co3+, and O-lattice/O-chemisorbed/O-physisorbed species. Coefficient of thermal expansion (CTE) analysis shows that the particular composition Sr1.97La0.03CoMoO6 has the lowest CTE value among the compositions studied. The electrical conductivity of Sr2CoMoO6 is enhanced effectively by doping La at Sr sites. The measured area-specific resistance (ASR) for the composition Sr1.97La0.03CoMoO6 (SLCM03) is found to be appreciably low, ∼0.053 Ohm cm–2 at 800 C. The obtained highest electrical conductivity with the lowest activation energy and low ASR value for the composition Sr1.97La0.03CoMoO6 encompasses it as a promising candidate for anode material in the intermediate-temperature solid oxide fuel cell (IT-SOFC) application.
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Scheelite type Sr1−xBaxWO4 (x = 0.1, 0.2, 0.3) for possible application in Solid Oxide Fuel Cell electrolytes

Authors Ahmed Afif, Juliana Zaini, Seikh Mohammad Habibur Rahman, Sten Eriksson, Md Aminul Islam & Abul Kalam Azad
Source
Scientific Reports
Volume: 9 Time of Publication: 2019
Abstract Polycrystalline scheelite type Sr1−xBaxWO4 (x = 0.1, 0.2 & 0.3) materials were synthesized by the solid state sintering method and studied with respect to phase stability and ionic conductivity under condition of technological relevance for SOFC applications. All compounds crystallized in the single phase of tetragonal scheelite structure with the space group of I41/a. Room temperature X-ray diffraction and subsequent Rietveld analysis confirms its symmetry, space group and structural parameters. SEM illustrates the highly dense compounds. Significant mass change was observed to prove the proton uptake at higher temperature by TG-DSC. All compound shows lower conductivity compared to the traditional BCZY perovskite structured materials. SBW with x = 0.3 exhibit the highest ionic conductivity among all compounds under wet argon condition which is 1.9  10−6 S cm−1 at 1000 C. Since this scheelite type compounds show significant conductivity, the new series of SBW could serve in IT-SOFC as proton conducting electrolyte.
Remark Article number: 9173 (2019)
Link

Surface Reconstruction under the Exposure of Electric Fields Enhances the Reactivity of Donor-Doped SrTiO3

Authors Buğra Kayaalp, Kurt Klauke, Mattia Biesuz, Alessandro Iannaci, Vincenzo M. Sglavo, Massimiliano D’Arienzo, Heshmat Noei, Siwon Lee, WooChul Jung, Simone Mascotto
Source
J. Phys. Chem. C
Volume: 123, Issue: 27, Pages: 16883-16892
Time of Publication: 2019
Abstract In the present work, we show how exposure to electric fields during a high-temperature treatment can be used to manipulate surface properties of donor-doped ceramics and thus improve their reactivity. La0.1Sr0.9TiO3 (LSTO) nanoparticles, prepared by hydrothermal synthesis, were consolidated under air with and without external electric fields. Although neither approaches caused grain growth upon consolidation, the treatment under the influence of the electric field (i.e., flash sintering) remarkably enhanced the segregation of Sr on the material’s surface. In addition, a high concentration of O– defects both in bulk as well as on the material surface was demonstrated by spectroscopic methods. This enhanced defect concentration along with the nanoscopic grain size of the field-consolidated materials is probably one of the triggering factors of their improved charge carrier mobility, as observed by impedance spectroscopy. The effect of such a perturbed defect structure on the reactivity of the materials was evaluated by the total oxidation of methane. For materials treated under the influence of electric fields, the catalytic reaction rate improved by a factor of 3 with respect to that of conventionally treated LSTO, along with a remarkable decrease of the activation energy. Thus, electric-field-assisted processes, usually known for their energy-saving character, can also be deemed as an attractive, forward-looking strategy for improving functional properties of ceramics.
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Metal oxides for thermoelectrics

Author Johannes Gutenberg
Source
Time of Publication: 2019
Remark Dissertation
Link

Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers

Authors Einar Vllestad, Ragnar Strandbakke, Mateusz Tarach, David Cataln-Martnez, Marie-Laure Fontaine, Dustin Beeaff, Daniel R. Clark, Jose M. Serra & Truls Norby
Source
Nature Materials
Volume: 18, Pages: 752–759
Time of Publication: 2019
Abstract Hydrogen production from water electrolysis is a key enabling energy storage technology for the large-scale deployment of intermittent renewable energy sources. Proton ceramic electrolysers (PCEs) can produce dry pressurized hydrogen directly from steam, avoiding major parts of cost-driving downstream separation and compression. However, the development of PCEs has suffered from limited electrical efficiency due to electronic leakage and poor electrode kinetics. Here, we present the first fully operational BaZrO3-based tubular PCE, with 10 cm2 active area and a hydrogen production rate above 15 Nml min−1. The novel steam anode Ba1−xGd0.8La0.2+xCo2O6−δ exhibits mixed p-type electronic and protonic conduction and low activation energy for water splitting, enabling total polarization resistances below 1 Ω cm2 at 600 C and Faradaic efficiencies close to 100% at high steam pressures. These tubular PCEs are mechanically robust, tolerate high pressures, allow improved process integration and offer scale-up modularity.
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