Published references
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All 1-25 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500 501-525 526-550 551-575 576-600 601-625 626-650 651-675 676-Modification of Ruddlesden-Popper-type Nd2-xNi0.75Cu0.2M0.05O4±δ by the Nd-site cationic deficiency and doping with Sc, Ga or In: Crystal structure, oxygen content, transport properties and oxygen permeability
ID=614| Authors |
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Journal of Solid State Chemistry
Volume: 296,
Pages: 121982 Time of Publication: 2021 |
| Abstract | Nd2-xNi0.75Cu0.2M0.05O4±δ (x ​= ​0 and 0.1; M ​= ​Sc, Ga, and In) Ruddlesden-Popper-type oxides are obtained by a sol-gel route and characterized concerning phase composition and crystal structure. It is found that the largest In3+ cannot be effectively introduced into the structure, while Nd stoichiometric and cation-deficient Nd2-xNi0.75Cu0.2Sc0.05O4±δ and Nd2-xNi0.75Cu0.2Ga0.05O4±δ (x ​= ​0; 0.1) can be obtained as single-phase materials. Systematic characterization of the crystal structure at high temperatures, oxygen content, as well as transport properties reveals that while the Nd-site deficiency has rather negligible influence on the structure, it causes a substantial decrease of the oxygen content, which at high temperatures leads to a change of the dominant type of defects from the oxygen interstitials to the vacancies for Nd1.9Ni0.75Cu0.2Sc0.05O4±δ and Nd1.9Ni0.75Cu0.2Ga0.05O4±δ. The Nd-site deficiency also causes a decrease of the total conductivity. Importantly, all the examined materials exhibit full chemical stability in CO2 atmosphere, which together with moderate thermal expansion makes them good candidates for the oxygen transport membranes, which can be used e.g. in the air separation technologies. The selected Sc- and Ga-doped compounds evaluated as ceramic membranes show relatively high oxygen fluxes, with the highest value of 0.78 ​mL ​cm-2 min-1 at ca. 880 ​°C registered for 0.9 ​mm thick, dense Nd1.9Ni0.75Cu0.2Ga0.05O4±δ membrane. |
| Keywords | Ruddlesden-Popper oxides; Nonstoichiometric compounds; Crystal structure; Transport properties; Oxygen permeation membranes |
| Remark | Link |
A heavily subtituted manganite in an ordered nanocomposite for long-term energy applications
ID=613| Authors |
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Research Square
Time of Publication: 2021
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| Abstract | The implementation of nano-engineered composite oxides opens up the way towards the development of a novel class of superior energy materials. Vertically aligned nanocomposites are characterized by a coherent, dense array of vertical interfaces, which allows for the extension of local effects to the whole volume of the material. Here, we use such a unique architecture to fabricate highly electrochemically active nanocomposites of lanthanum strontium manganite and doped ceria with unprecedented stability and straight applicability as functional layers in solid state energy devices. Direct evidence of synergistic local effects for enhancing the electrochemical performance, stemming from the highly ordered phase alternation, is given here for the first time using atom-probe tomography combined with oxygen isotopic exchange. Interface-induced cationic substitution, enabling lattice stabilization, is presented as the origin of the observed long-term stability. These findings reveal a novel route for materials nano-engineering based on the coexistence between local disorder and long-range arrangement. |
| Keywords | Nano-engineered composite oxides; Energy materials; Nanocomposites |
| Remark |
DOI: https://doi.org/10.21203/rs.3.rs-134793/v1 Link |
Improved environmental stability of thermoelectric ceramics based on intergrowths of Ca3Co4O9–Na0.75CoO2
ID=612| Authors |
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Ceramics International
Volume: 47,
Issue: 8,
Pages: 11687-11693 Time of Publication: 2021 |
| Abstract | Ceramics based on calcium and sodium cobaltates are promising high-temperature thermoelectric oxide materials with complementary advantages. Ca3Co4O9 is stable at high temperatures, whereas Na0.75CoO2 can be easily processed as a textured ceramic with excellent thermoelectric properties. Na0.75CoO2, however, lacks long-term stability and degrades in even a relatively mild humid environment. In this work, we present a novel approach to the synthesis of complex composite materials based on intergrowths of sodium and calcium cobaltates that have excellent thermoelectric performance and improved stability. We synthesized samples with the mixed composition (3-x)Ca3Co4O9–4x(Na0.75CoO2) in an over-pressured oxygen atmosphere. Samples with the mixed Ca–Na composition developed textured microstructures composed of intergrowths of both end-members, as revealed by transmission electron microscopy. We also examined the thermoelectric performance of the investigated materials after exposure to high humidity and found that the composition with x = 0.8 (Ca:Na = 2.75) has long-term stability. |
| Keywords | Composite materials; Microstructure; Transmission electron microscopy; Thermoelectric |
| Remark | Link |
Time-Enhanced Performance of Oxide Thermoelectric Modules Based on a Hybrid p–n Junction
ID=611| Authors |
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ACS Omega
Volume: 6,
Issue: 1,
Pages: 197–205 Time of Publication: 2020 |
| Abstract | The present challenge with all-oxide thermoelectric modules is their poor durability at high temperatures caused by the instability of the metal-oxide interfaces at the hot side. This work explains a new module concept based on a hybrid p–n junction, fabricated in one step by spark plasma co-sintering of Ca3Co4–xO9+δ (CCO, p-type) and CaMnO3−δ/CaMn2O4 (CMO, n-type). Different module (unicouple) designs were studied to obtain a thorough understanding of the role of the in situ formed hybrid p–n junction of Ca3CoMnO6 (CCMO, p-type) and Co-oxide rich phases (p-type) at the p–n junction (>700 °C) in the module performance. A time-enhanced performance of the modules attributed to this p–n junction formation was observed due to the unique electrical properties of the hybrid p–n junction being sufficiently conductive at high temperatures (>700 °C) and nonconductive at moderate and low temperatures. The alteration of module design resulted in a variation of the power density from 12.4 (3.1) to 28.9 mW/cm2 (7.2 mW) at ΔT ∼ 650 °C after 2 days of isothermal hold (900 °C hot side). This new concept provides a facile method for the fabrication of easily processable, cheap, and high-performance high-temperature modules. |
| Remark | Link |
Comparative investigation on the functional properties of alkaline earth metal (Ca, Ba, Sr) doped Nd2NiO4+δ oxygen electrode material for SOFC applications
ID=610| Authors |
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Journal of Alloys and Compounds
Volume: 860,
Pages: 158490 Time of Publication: 2021 |
| Abstract | Functional properties of Nd2NiO4+δ based materials doped with different alkaline earth metal ions for SOFC applications is studied extensively and compared in this article. Phase pure powders of Nd2NiO4 +δ and Nd1.7A0.3NiO4+δ (A=Ca, Sr and Ba) were synthesized by solid state route at 1250 °C from the constituent precursor oxides and carbonates. Good compatibility of these cathode materials with GDC electrolyte is confirmed through XRD analysis of the composite powder heat treated at 1250 °C. Electrical conductivity of undoped Nd2NiO4+δ is found to attain a maximum at ~470 °C and then decreases noticeably with increase in temperature. The decrease in conductivity at higher temperatures is not significant for alkaline earth metal ion doped systems. In the lower temperature range, electrical conductivity decreases with alkaline earth metal ion doping and this decrement is more as the size of the dopant cation increases with an exception for Sr doped samples. However, at the operating temperature of the fuel cell (say 800 °C) electrical conductivity of Ca and Sr doped Nd2NiO4+δ are higher than the undoped material. Polarization resistance of the cathode materials are evaluated from the measured impedance spectra of symmetric cells and activation energy for oxygen reduction reaction is calculated from the Arrhenius plot of polarization resistance. Activation energy decreases with alkaline earth metal ion doping and this decrease is more in case of Ca doping followed by Sr and Ba doping. Electrolyte supported button cells fabricated under identical processing conditions were tested at 800 °C; highest power density of 188 mW cm−2 is obtained for the cell having Ca doped Nd2NiO4+δ as oxygen electrode. |
| Keywords | SOFC; Air electrode; Nd2NiO4; Area specific resistance; I-V characteristics |
| Remark |
https://doi.org/10.1016/j.jallcom.2020.158490 Link |
Synthesis and processing of SOFC components for the fabrication and characterization of anode supported cells
ID=609| Authors |
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Boletín de la Sociedad Española de Cerámica y Vidrio
Time of Publication: 2020
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| Abstract | In this article, it is intended to evaluate the performances of previously synthesized different nanometric compounds as SOFC components under real conditions. For this purpose, anodic supports SOFCs have been manufactured in different configurations. The compounds NiO-(Y2O3)0.08(ZrO2)0.92 (NiO–YSZ), (Y2O3)0.08(ZrO2)0.92 (YSZ), Sm0.2Ce0.8O1.9 (SDC), La0.6Sr0.4FeO3 (LSF) and LaNi0.6Fe0.4O3 (LNF) were used as anode support, electrolyte, barrier, cathode and contact layer, respectively. To obtain the cells, the anode supports were produced by uniaxial pressing and the remaining layers were added using the airbrush technique, assembling them by different sintering processes. The cells developed have been electrochemically tested in a temperature range between 750 and 865 °C. Additionally, degradation tests have been carried out under constant current. Moreover, to characterize the microstructure of the cells, a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX) analyzer has been used. The results obtained show that the incorporation of cathode and contact layers increases the power densities and decreases the total resistances of the cells with respect to the cell without cathode, especially with the addition of the LNF contact layer. Despite the improvement obtained, more tests have to be carried out in order to optimize the performance of SOFC devices in degradation tests. |
| Keywords | Solid oxide fuel cells; Processing; Composite; Degradations; Electrochemical impedance spectra |
| Remark |
Available online 22 December 2020 Link |
Increasing the thermal expansion of proton conducting Y-doped BaZrO3 by Sr and Ce substitution
ID=608| Authors |
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Solid State Ionics
Volume: 359,
Pages: 115534 Time of Publication: 2021 |
| Abstract | Proton conducting oxide electrolytes find potential application in proton ceramic fuel cells and electrolyzers operating at intermediate temperatures, e.g. 400–600 °C. However, state-of-the-art proton conducting ceramics based on Y-doped BaZrO3 (BZY) have lower thermal expansion coefficient (TEC) than most commonly applied or conceived supporting electrode structures, making the assembly vulnerable to degradation due to cracks or spallation. We have increased the TEC of 20 mol% Y-doped BZY (BZY20) by partially substituting Ba and Zr with Sr and Ce, respectively, to levels which still maintain the cubic structure and sufficiently minor n-type conduction; (Ba0.85Sr0.15)(Zr0.7Ce0.1Y0.2)O2.9 (BSZCY151020). High temperature XRD shows that this material has a cubic structure (space group ) in the temperature range of 25–1150 °C and a linear TEC of ~10 × 10−6 K−1, as compared to the ~8 × 10−6 K−1 for BZY. It exhibited a DC conductivity of ~5 mS cm−1 at 600 °C in wet H2. This electrolyte with increased TEC may find application in proton ceramic electrochemical cells in general and metal supported ones in particular. |
| Keywords | Barium zirconate; BZY; Thermal expansion coefficient; TEC; Conductivity; Proton; Proton ceramic electrochemical cells; Metal-supported |
| Remark |
https://doi.org/10.1016/j.ssi.2020.115534 Link |
Properties of Barium Cerate Thin Films Formed Using E-Beam Deposition
ID=607| Authors |
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Crystals
Volume: 10,
Pages: 1152 Time of Publication: 2020 |
| Abstract | This article focuses on the properties of the BaCeO3 thin films formed by electron-beam vapor deposition and investigates the formation of barium cerates on supports with different thermal expansion coefficients (Stainless Steel, Invar, Glass Sealing, and Inconel substrates) and the influence of the technological parameters on the properties of the formed thin films with an emphasis on the stability of the films. Morphology and phase composition and mechanical and electrical properties were investigated. It was found that the main factors influencing the phase composition and morphology of the films are the temperature of the support and the deposition rate. However, the mechanical properties of the films are mostly influenced by strains introduced to thin films by using different supports. Two interesting features of the electrical properties of the studied strained films were noticed: the film with the highest in-plane tensile strain showed the lowest activation energy of total conductivity, whereas the film with the lowest strain showed the highest value of total conductivity. |
| Remark | Link |
Reversible fuel electrode supported solid oxide cells fabricated by aqueous multilayered tape casting
ID=606| Authors |
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J. Phys. Energy
Volume: 3,
Issue: 2,
Pages: 024002 Time of Publication: 2021 |
| Abstract | Fuel electrode supported solid oxide cells (SOCs) have been developed on an industrial scale using the aqueous tape-casting technique. The NiO–yttria-stabilized zirconia Y2O3–ZrO2 (YSZ) fuel electrode and YSZ electrolyte have been manufactured by multilayer co-laminated tape casting. Details of the tape-casting slurry formulations are described and discussed. Two types of cells were fabricated with different microstructures of the NiO–YSZ support discussed. Good electrochemical performance and stability in SOFC mode at 750 °C and 0.7 V for both button cells reaching around >0.75 W cm−2 and with no measurable degradation after >700 h were observed. The selected cell was scaled up to large-area cells (36 cm2 of the active area) and electrochemically tested at 750 °C in a single repetition unit (SRU) in SOFC (Solid Oxide Fuel Cell), SOEC (Solid Oxide Electrolysis Cell) and co-SOEC (Solid Oxide co-Electrolysis Cell) mode, and in a short-stack of two SRUs in SOFC mode. A current up to 17 A was obtained at 1.4 V (0.7 V cell−1) with the short-stack configuration in SOFC mode, corresponding to ∼0.5 A cm−2 and 24 W. The performances of the aqueous-based SOC cells can be considered highly remarkable, thus supporting the success in scaling the fabrication of SOC stacks using more environmentally friendly processes than conventional ones. |
| Remark | Link |
Towards efficient oxygen separation from air: Influence of the mean rare-earth radius on thermodynamics and kinetics of reactivity with oxygen in hexagonal Y1-xRxMnO3+δ
ID=605| Authors |
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Acta Materialia
Volume: 205,
Pages: 116544 Time of Publication: 2021 |
| Abstract | It is documented that the mean radius of rare-earth cations occupying Y1-xRx sublattice in Y1-xRxMnO3+δ hexagonal oxides plays a decisive role in terms of thermodynamics and kinetics of reactivity of the materials with oxygen, and consequently, influences strongly the oxygen storage performance in thermal swing processes conducted in oxygen and air. Y1-xRxMnO3+δ samples with designed being close to the critical one, at the border of stability between hexagonal- and perovskite-type phases, can reversibly incorporate/release significant amounts of oxygen in pure O2 or air atmospheres, at the moderate temperatures on the order of 200–300 °C. Characteristic temperatures of oxidation and reduction are dependent on , therefore, it is possible to adjust conditions of the temperature swing operation by the chemical doping in Y1-xRxMnO3+δ with larger rare-earth elements. Crucial from a practical point of view, an increase of the oxidation temperature in such compounds greatly enhances the speed of the oxidation process (20 °C increase can reduce half-time of oxidation twice), which is found to be the limiting factor concerning the performance. Based on the comprehensive studies of the physicochemical properties of Y1-xRxMnO3+δ, the optimized Y0.95Pr0.05MnO3+δ composition is proposed, doped only with a small amount of more expensive praseodymium. The material exhibits excellent oxygen storage-related properties and is able for the effective production of oxygen in air by the thermal swing process, utilizing medium-/low-temperature industrial waste heat. |
| Remark | Link |
Tuning the RWGS Reaction via EPOC and In Situ Electro-oxidation of Cobalt Nanoparticles
ID=604| Authors |
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ACS Catal.
Volume: 10,
Issue: 24,
Pages: 14916–14927 Time of Publication: 2020 |
| Abstract | The electrochemical promotion of catalytic activity by non-noble transition metals is rarely reported in the literature. Here, Co nanoparticles were utilized for the electrochemical activation of CO2 hydrogenation under atmospheric pressure conditions. A range of transient kinetic experiments in conjunction with X-ray photoelectron spectroscopy and imaging techniques were employed to correlate the observed catalytic activity with the electronic and morphological characteristics of the cobalt catalyst surface. Our results show that migrating ions from the solid electrolyte to the catalyst surface has a dual effect, which has an impact on the observed catalytic behavior. First, they lead to an electrochemically formed double layer on the catalyst surface, which effectively modifies the catalyst work function and consequently alters the observed catalytic rate. Second, they have a profound effect on the oxidation state of cobalt and therefore on the structure of the cobalt oxide particles formed. The presence of Co oxide phases upon anodic polarization shows up to a 5-fold increase in the catalytic rate of the reverse water gas shift (RWGS) reaction. The enhancement of the catalytic activity observed in this work, with a relatively inexpensive cobalt oxide film, is comparable to that obtained with noble metal catalysts in classical EPOC studies. The present study also demonstrates that the formation of different oxide phases can be controlled accurately by electrochemical means and used to tune the catalytic activity and selectivity of cobalt. The reported results could guide the design and operation of more selective and active catalytic processes for the RWGS reaction. |
| Keywords | electrochemical promotion, cobalt oxide, CO2 hydrogenation, XPS, RWGS |
| Remark | Link |
From insulator to oxide-ion conductor by a synergistic effect from defect chemistry and microstructure: acceptor-doped Bi-excess sodium bismuth titanate Na0.5Bi0.51TiO3.015
ID=603| Authors |
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Journal of Materials Chemistry A
Issue: 47
Time of Publication: 2020
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| Abstract | The influence of Ti-site acceptor-doping (Mg2+, Zn2+, Sc3+, Ga3+ and Al3+) on the electrical conductivity and conduction mechanism of a nominally Bi-excess sodium bismuth titanate perovskite, Na0.5Bi0.51TiO3.015 (NB0.51T), is reported. Low levels of acceptor-type dopants can introduce appreciable levels of oxide-ion conductivity into NB0.51T, i.e., 0.5% Mg-doping for Ti4+ can enhance the bulk conductivity of NB0.51T by more than 3 orders of magnitude with the oxide-ion transport number going from <0.1 for NB0.51T to >0.9 at 600 °C. The intriguing electrical behaviour in acceptor-doped NB0.51T dielectrics is a synergistic effect based on the defect chemistry and ceramic microstructure in these materials. NB0.51T ceramics with extremely low levels of doping show an inhomogeneous microstructure with randomly distributed large grains embedded in a small grained matrix. This can be considered as a two-phase composite with large grains as a conductive phase and small grains as an insulating phase based on an empirical conductivity – grain size relationship. Variation in the fraction of the conductive, large grained phase with increasing doping levels agrees with the oxide-ion transport number. This electrical two-phase model is supported by finite element modelling. This study reveals the significance of ceramic microstructure on the electrical conduction behaviour of these materials and can provide a guideline for selecting suitable doping strategies to meet the electrical property requirements of NBT-based ceramics for different applications. |
| Remark | Link |
Thermally stable, low resistance Mg2Si0.4Sn0.6/Cu thermoelectric contacts using SS 304 interlayer by one step sintering
ID=602| Authors |
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Materials Research Bulletin
Volume: 136,
Pages: 111147 Time of Publication: 2021 |
| Abstract | Device fabrication using Mg2Si1-xSnx thermoelectric (TE) material for 600–800 K application requires stable and low resistance electrical contacts between TE legs and the electrodes. In this study, n-type Mg2Si0.38Sn0.6Bi0.02 was hot-pressed with Cu electrodes in a single step, resulting in Cu3Mg2Si and Cu4MgSn phases at the interface. Although the specific contact resistance (rc) across the interface was 4.4 ± 0.9 μΩ.cm2, the electrical resistivity of the TE leg increased by approximately 60 % due to Cu diffusion through the interface. Incorporating the SS304 interlayer to prevent Cu diffusion increased rc to 6.1 ± 2 μΩ.cm2. Upon annealing at 723 K for 3–15 days, rc remained at <10 μΩ.cm2 with an approximately 15 % decrease in the power factor. However, without SS304, rc increased to 41.5 ± 18 μΩ.cm2, with 65 % reduction in the power factor. Thus, this work demonstrates the fabrication of thermally stable Cu/Mg2Si0.4Sn0.6 joints by using the SS304 interlayer in a single-step process. |
| Remark | Link |
NiO–ZnO based junction interface as high-temperature contact materials
ID=601| Author |
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Ceramics International
Volume: 47,
Issue: 6,
Pages: 8053-8059 Time of Publication: 2021 |
| Abstract | Contact materials play a crucial role in an electronic device operating at moderate and elevated temperatures where chemical and thermal stability is of great importance. Oxide materials and their interfaces are potential candidates as high-temperature contact materials due to their high chemical and thermal stabilities. In this work, polycrystalline oxides of Ni0.98Li0.02O and Zn0.98Al0.02O were used to make junction interfaces, where the solid-state synthesis method was used to obtain the individual oxide materials. After assembly of the junction interfaces, properties such as electrical, chemical, and thermal stabilities of the interfaces were investigated. The electrical properties were assessed through current-voltage (I–V) and electrochemical impedance spectroscopy (EIS) measurements, where the interface revealed a transition from electrically rectifying to slightly ohmic contact within a temperature range from 500–1000 °C. After annealing the junction interfaces at these elevated temperatures, no secondary phase was observed at the junction interface, i.e., the interfaces remain chemically stable. Moreover, the effect of isothermal annealing on the I–V characteristics curve of the junction showed an increased reverse current output over long annealing time, attributed mainly to the increased effective contact area at the junction interface and cation inter-diffusion processes. Furthermore, an investigation of the cation inter-diffusion mechanism revealed mainly lattice diffusion of Zn2+ into Ni0.98Li0.02O, while Ni2+ diffusion into Zn0.98Al0.02O exhibited both lattice and grain-boundary diffusion mechanisms. |
| Keywords | Interfaces; Thermal stability; Electrical properties; Diffusion |
| Remark | Link |
Processing Ceramic Proton Conductor Membranes for Use in Steam Electrolysis
ID=600| Authors |
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Membranes
Volume: 10,
Issue: 11,
Pages: 339 Time of Publication: 2020 |
| Abstract | Steam electrolysis constitutes a prospective technology for industrial-scale hydrogen production. The use of ceramic proton-conducting electrolytes is a beneficial option for lowering the operating temperature. However, a significant challenge with this type of electrolyte has been upscaling robust planar type devices. The fabrication of such multi-layered devices, usually via a tape casting process, requires careful control of individual layers’ shrinkages to prevent warping and cracks during sintering. The present work highlights the successful processing of 50 × 50 mm2 planar electrode-supported barium cerium yttrium zirconate BaZr0.44Ce0.36Y0.2O2.9 (BZCY(54)8/92) half cells via a sequential tape casting approach. The sintering parameters of the half-cells were analyzed and adjusted to obtain defect-free half-cells with diminished warping. Suitably dense and gas-tight electrolyte layers are obtained after co-sintering at 1350 °C for 5 h. We then assembled an electrolysis cell using Ba0.5La0.5CoO3−δ as the steam electrode, screen printed on the electrolyte layer, and fired at 800 °C. A typical Ba0.5La0.5CoO3−δ|BaZr0.44Ce0.36Y0.2O3−δ(15 μm)|NiO-SrZr0.5Ce0.4Y0.1O3−δ cell at 600 °C with 80% steam in the anode compartment reached reproducible terminal voltages of 1.4 V @ 500 mA·cm−2, achieving ~84% Faradaic efficiency. Besides electrochemical characterization, the morphology and microstructure of the layered half-cells were analyzed by a combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy. Our results also provide a feasible approach for realizing the low-cost fabrication of large-sized protonic ceramic conducting electrolysis cells (PCECs). |
| Remark | Link |
Cation-driven electrical conductivity in Ta-doped orthorhombic zirconia ceramics
ID=599| Authors |
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Ceramics International
Volume: 47,
Issue: 5,
Pages: 7248-7252 Time of Publication: 2021 |
| Abstract | This paper is devoted to the study of the electrical conductivity of tantalum-doped zirconia ceramics prepared by spark plasma sintering. In this study, the temperature dependence of conductivity in as-prepared specimens and in those previously annealed in air is determined and compared. A semi-empirical model, which is based on the oxidation states of the cations, has been developed and successfully assessed. According to this, the conductivity is basically controlled by the diffusion of tetravalent zirconium cations in both cases, although the concentration of these species varies drastically with the amount of induced oxygen vacancies. This is a quite unexpected fact, since conductivity is normally controlled by anionic diffusion in zirconia ceramics. This option is forbidden here due to the presence of substitutional pentavalent cations. Therefore, conductivity values are much lower than those reported in trivalent or divalent substitutional cation doped zirconia ceramics. |
| Remark | Link |
Direct Solid Oxide Electrolysis of Carbon Dioxide:Analysis of Performance and Processes
ID=598| Authors |
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Processes
Volume: 8,
Pages: 1390 Time of Publication: 2020 |
| Abstract | Chemical industries rely heavily on fossil resources for the production of carbon-basedchemicals. A possible transformation towards sustainability is the usage of carbon dioxide as asource of carbon. Carbon dioxide is activated for follow-up reactions by its conversion to carbonmonoxide. This can be accomplished by electrochemical reduction in solid oxide cells. In thiswork, we investigate the process performance of the direct high-temperature CO2electrolysis bycurrent-voltage characteristics (iV) and Electrochemical Impedance Spectroscopy (EIS) experiments.Variations of the operation parameters temperature, load, fuel utilization, feed gas ratio and flowrate show the versatility of the procedure with maintaining high current densities of 0.75 up to1.5 A·cm−2, therefore resulting in high conversion rates. The potential of the high-temperature carbondioxide electrolysis as a suitable enabler for the activation of CO2as a chemical feedstock is thereforeappointed and shown. |
| Remark | Link |
Structural, optical, and dielectric properties of Bi2O3-K2O-TiO2-P2O5 glasses and related glass-ceramics
ID=597| Authors |
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Phase Transitions
Volume: 93,
Issue: 10-11
Time of Publication: 2020
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| Abstract | The glasses in the Bi2O3-K2O-TiO2-P2O5 system were elaborated by the conventional quenching method. Their structure was studied by Raman spectroscopy, and additional information is determined from density measurements and thermal analysis. The optical absorption of the glasses is investigated and it is found that the optical gap and the Urbach energy decrease and increase, respectively, with increasing Bi2O3 content. The crystallization of the glasses was performed under controlled heat treatments to develop glass-ceramics. Their dielectric constants are carried out by impedance spectroscopy. The variations of the permittivity (ϵr) and the dielectric loss (tanδ) versus frequency and temperature are determined. It is evidenced that the introduction of Bi2O3 in the glasses diminished the dispersion at low frequencies. The presence of bismuth oxide in the materials is also beneficial since it allowed the formation of glass-ceramics with high dielectric constant and low dielectric loss. |
| Remark | Link |
Strategies to Mitigate the Degradation of Stainless-SteelInterconnects Used in Solid Oxide Fuel Cells
ID=596| Author |
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Time of Publication: 2020
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| Abstract | Interconnects are a vital part of solid oxide fuel cells (SOFC), where they electricallyconnect individual cells to form a fuel cell stack. They are a main contributor to theoverall stack cost and the limited life-time of fuel cells, and, therefore, improvementscarried out on the interconnect level could further the commercialization of SOFCs.The limited life-time of the interconnect is related to the material used today, ferriticstainless steels (FSS). FSS interconnects are more cost-effective than previously usedceramics, but they degrade under the conditions prevalent in an SOFC: high temperaturesbetween 600°C and 850°C, and a p(O2) gradient. Certain corrosion phenomena thatoccur, such as Cr evaporation and continuous oxide scale growth, negatively impact cellperformance due to cathode poisoning and increased electrical resistance, respectively.These phenomena have been found to be effectively mitigated by coatings, such as the(Co,Mn)3O4(MCO) coating, or reactive element coatings, such as Ce.The present thesis examines these coatings with regard to three aspects: (i) doesthe semi-conducting spinel coating affect the electrical resistance of the interconnectnegatively, or is its conductivity negligible in comparison to the continuously growingCr2O3scale below it; (ii) does the coating self-heal if it is cracked even at intermediatetemperatures, i.e. 650°C and 750°C, or do the cracks persist and increase Cr evaporation;and (iii) is the long-term stability of the state-of-the-art Ce/Co coating (10 nm Ce/640 nmCo) still effective after 35 000 h, or not. The second aspect is not only important tounderstand corrosion behavior, but it would also allow for large-scale roll-to-roll PVDcoating, which is significantly more cost-effective than batch coating.Another corrosion phenomenon that is elucidated within the scope of this work is thedual atmosphere effect. This effect leads to increased corrosion on the air-facing side ofthe interconnect if the FSS is exposed to a dual atmosphere, i.e. air on one side andhydrogen on the other side, compared to if the FSS is exposed to an air-only atmosphere.A new theory as to why the dual atmosphere effect occurs is proposed, and it is indirectlyverified by means of excluding all other possibilities. Factors that influence the dualatmosphere effect are discussed, and it is shown how the dual atmosphere effect could, inpart, be mitigated. |
| Keywords | Solid Oxide Fuel Cell; Corrosion; Interconnect; Cr Evaporation; Area SpecificResistance; Deformation; Long-term; Dual Atmosphere; Hydrogen |
| Remark |
THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Link |
Processing and properties of translucent bismuth sodium titanate ceramics
ID=595| Authors |
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Journal of the European Ceramic Society
Volume: 41,
Issue: 2,
Pages: 1221-1229 Time of Publication: 2021 |
| Abstract | Lead-free bismuth sodium titanate piezoceramics were processed by a solid-state route with a novel precursor approach. By carefully controlling the processing parameters and sintering atmospheres, translucent ceramics with pore-free, homogeneous microstructures with exceptionally low dielectric loss at elevated temperatures. The pore-free microstructure can influence the operating life of a dielectric device positively, since pores and other microstructural defects are usually responsible for material failures within devices. Synchrotron and surface X-ray diffraction experiments revealed a clear dependence of the crystal structure on sintering parameters and defect chemistry. Microstructural analysis showed a dependency of a secondary phase on the sintering atmosphere. The grain size could be adjusted using a shortened grinding process instead of using the common methods like increasing calcining or sintering temperature. |
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Mitigation of grain boundary resistance inLa2/3-xLi3xTiO3perovskite as an electrolyte forsolid-state Li-ion batteries
ID=594| Authors |
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| Source |
J Mater Sci Energy materials
Pages: 2435–2450 Time of Publication: 2021 |
| Abstract | In this work, we report that modification of the chemical composition of grainboundaries of La2/3-xLi3xTiO3double perovskite, one of the most promising Li-ion conducting solid electrolytes, can be a convenient and versatile way ofcontrolling the space charge potential, leading to a mitigated electrical resistanceof the grain boundaries. Two groups of additives are investigated: lithium-enriching agents (Li3BO3, LiF) and 3dmetal ions (Co2?,Cu2?), both expected toreduce the Schottky barrier. It is observed that Li-containing additives workeffectively at a higher sintering temperature of 1250°C. Regarding copper, itshows a much stronger positive impact at lower temperature, 1150°C, while theaddition of cobalt is always detrimental. Despite overall complex behavior, it isdocumented that the decreased space charge potential plays a more importantrole in the improvement of lithium conduction than the thickness of the grainboundaries. Among the proposed additives, modification of La2/3-xLi3xTiO3by2 mol.% Cu2?results in the space charge potential reduction by 32 mV inrelation to the reference sample, and the grain boundary specific conductivityincrease by 80%, as measured at 30°C. Introduced additive allows to obtain asimilar effect on the conductivity as elevating the sintering temperature, whichcan facilitate manufacturing procedure. |
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Crystal structures and proton transport properties of Sr2(Ti1-xMx)O4-δ (M = Fe, Al)
ID=593| Authors |
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Solid State Sciences
Volume: 108,
Pages: 106407 Time of Publication: 2020 |
| Abstract | This study focuses on the effects of acceptor dopants in proton-conductive Sr2TiO4-based layered perovskites. We synthesized Sr2Ti0.9Fe0.1O4-δ (STF10) and Sr2Ti0.95Al0.05O4-δ (STA05) and evaluated the influence of ion substitution on their crystal structures, electrical conductivities, and proton transport properties. Our obtained results suggest that a redox reaction is the more favorable mechanism for the introduction of proton defects to Fe-doped samples compared with water vapor absorption, while the reverse is true for Al-doped samples. STF10 was found to exhibit a larger electrical conductivity at low temperatures than STA05. In addition, STF10 presented a proton transport number of 0.5 at 600 °C, while the corresponding value for STA05 was 0.5–0.6 at 450–600 °C. The higher proton transport number of STA05 at 450–550 °C compared to that of STF10 indicates that the Al-dopant suppressed the electronic conductivity owing to its constant valency. We therefore considered that characterization of the changes in material properties related to ion substitution can serve as a guide for material selection when developing proton-conducting solid oxide fuel cell technologies. |
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Dynamics of Hydroxyl Anions Promotes Lithium Ion Conduction in Antiperovskite Li2OHCl
ID=592| Authors |
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Chem. Mater.
Volume: 32,
Issue: 19,
Pages: 8481–8491 Time of Publication: 2020 |
| Abstract | Li2OHCl is an exemplar of the antiperovskite family of ionic conductors, for which high ionic conductivities have been reported, but in which the atomic-level mechanism of ion migration is unclear. The stable phase is both crystallographically defective and disordered, having ∼1/3 of the Li sites vacant, while the presence of the OH– anion introduces the possibility of rotational disorder that may be coupled to cation migration. Here, complementary experimental and computational methods are applied to understand the relationship between the crystal chemistry and ionic conductivity in Li2OHCl, which undergoes an orthorhombic to cubic phase transition near 311 K (≈38 °C) and coincides with the more than a factor of 10 change in ionic conductivity (from 1.2 × 10–5mS/cm at 37 °C to 1.4 × 10–3 mS/cm at 39 °C). X-ray and neutron experiments conducted over the temperature range 20–200 °C, including diffraction, quasi-elastic neutron scattering (QENS), the maximum entropy method (MEM) analysis, and ab initio molecular dynamics (AIMD) simulations, together show conclusively that the high lithium ion conductivity of cubic Li2OHCl is correlated to “paddlewheel” rotation of the dynamic OH– anion. The present results suggest that in antiperovskites and derivative structures a high cation vacancy concentration combined with the presence of disordered molecular anions can lead to high cation mobility. |
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Conduction properties of acceptor-doped BaTiO3–Bi(Zn1/2Ti1/2)O3-based ceramics
ID=591| Authors |
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Journal of Materials Science
Volume: 55,
Pages: 16290–16299 Time of Publication: 2020 |
| Abstract | A series of acceptor-doped ceramics based on the solid solution, (1-x)BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT-BZT), where x = 0.1, 0.2, 0.3, 0.4, were prepared via solid-state synthesis to investigate the effect of doping and BZT content on conduction properties. Impedance spectroscopy measurements showed an increase in conductivity through acceptor doping with Mg on the Ti-site (Mg′′Ti). Ceramics of the composition, 0.80BaTiO3–0.20Bi(Zn1/2Ti1/2)O3 with 3 mol% Mg′′Ti, showed the highest conductivity in this study at 1.28 mScm−1 (~ 600 °C), an order of magnitude improvement over the stoichiometric composition. Variable pO2 impedance measurements revealed p-type conductivity in the grain while EMF measurements showed that above ~ 550 °C, ions are the dominant charge carriers (transference number, ti = 0.91 at 735 °C). Similarly, all 3 mol% Mg-doped compositions above x = 0.1 were primarily ionic conductors with transference numbers above ti = 0.79 (735 °C). X-ray diffraction data showed a pseudocubic primary phase for all samples with evidence of additional impurity phases accompanying samples with 3 mol% Mg′′Ti or greater. |
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Stabilized Charge, Spin, and Orbital Ordering by the 6s2 Lone Pair in Bi0.5Pb0.5MnO3
ID=590| Authors |
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Inorg. Chem.
Volume: 59,
Issue: 18,
Pages: 13390–13397 Time of Publication: 2020 |
| Abstract | Bi and Pb ions with charge degree of freedom depending on 6s2 and 6s0 electronic configurations were combined with the Mn ion in a perovskite oxide. Comprehensive theoretical and experimental investigations revealed the Bi3+0.5Pb2+0.5Mn3+0.5Mn4+0.5O3 charge ordered state with CE-type spin and dz2 orbital orderings as observed in La0.5Ca0.5MnO3, Nd0.5Sr0.5MnO3, and Bi0.5Sr0.5MnO3. The charge and orbital orderings were preserved above 500 K owing to the stereochemical activity of Bi3+ and Pb2+ ions which stabilized the structural distortion. |
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