Electrolyte Microstructure Research Articles

Effect of sintering temperature on the microstructure and ionic conductivity of Ce0.8Sm0.1Ba0.1O2-δ electrolyte

This study investigated the effects of sintering temperature on the microstructure and ionic conductivity of codoped ceria electrolyte with barium and samarium as dopants. The electrolyte (Ce0.8Sm0.1Ba0.1O2-δ) powder was synthesized using the citric acid-nitrate combustion method and calcined at 900°C for 5 h. The calcined electrolyte exhibited a cubic fluorite crystal structure with some impurity phases. The calcined powder was then pressed into cylindrical pellets using uniaxial die-pressing. The pellets were sintered at three different temperatures, i.e., 1200, 1300 and 1400°C for 5 h. Microstructural analysis of the pellets showed that the average grain size increased with the increase in sintering temperature. The sintered densities of the pellets were measured by Archimedes’ method, and the relative density values were within the range of 78%TD to 87%TD as the sintering temperature increased from 1200 to 1400°C. Electrochemical impedance spectroscopy analysis showed that conductivity increased with the increase in sintering temperature, but no considerable change in conductivity was observed for the pellets sintered at 1300 and 1400°C. The results revealed that the electrolyte pellet sintered at 1300°C exhibited the ionic conductivity of 0.005 S/cm with lowest activation energy of 0.7275 eV.

Conductivity and Microstructure of Li Doped Thick Film Ceria Electrolyte

Conductivity and Microstructure of Li Doped Thick Film Ceria Electrolyte

Influence of microstructure and AlPO4 secondary-phase on the ionic conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid-state electrolyte

A ceramic solid-state electrolyte of lithium aluminum titanium phosphate with the composition of Li[Formula: see text]Al[Formula: see text]Ti[Formula: see text](PO[Formula: see text] (LATP) was synthesized by a sol–gel method using a pre-dissolved Ti-source. The annealed LATP powders were subsequently processed in a binder-free dry forming method and sintered under air for the pellet preparation. Phase purity, density, microstructure as well as ionic conductivity of the specimen were characterized. The highest density (2.77[Formula: see text][Formula: see text] with an ionic conductivity of [Formula: see text] (at 30[Formula: see text]C) was reached at a sintering temperature of 1100[Formula: see text]C. Conductivity of LATP ceramic electrolyte is believed to be significantly affected by both, the AlPO4 secondary phase content and the ceramic electrolyte microstructure. It has been found that with increasing sintering temperature, the secondary-phase content of AlPO4 increased. For sintering temperatures above 1000[Formula: see text]C, the secondary phase has only a minor impact, and the ionic conductivity is predominantly determined by the microstructure of the pellet, i.e. the correlation between density, porosity and particle size. In that respect, it has been demonstrated, that the conductivity increases with increasing particle size in this temperature range and density.

Reduced Temperature Sintering of GDC Electrolyte for IT-SOFCs

Lanthanide material- (gadolinium or samarium) doped ceria (GDC or SDC) is considered one of the most advanced electrolyte materials for intermediate temperature (below 700 oC) SOFC (IT-SOFC) because of its high ionic conductivity at these temperatures. However, a high sintering temperature (above 1400 oC) is a disadvantage of the doped ceria. Metal oxides such as Fe oxide, Co oxide, Mn oxide, Li oxide, Ga oxide and Cu oxide were used as sintering aids to obtain the fully sintered electrolytes at a lower sintering temperature. In this study, the effect of a copper additive as a sintering aid to lower the sintering temperature for the construction of solid oxide fuel cells (SOFCs) was investigated. Gd-doped ceria (GDC) electrolyte with 0.25-10 mol% CuO sintering aid was prepared by reacting GDC power and copper nitrate solution followed by heating at 600 oC. The sintering of CuO-coated GDC powder was optimized by investigating linear shrinkage, microstructure, grain size, ionic conductivity, and activation energy of CuO-GDC electrolytes at temperatures ranging from 1100 to 1400 ¢ªC. The addition of Cu additive in GDC powder led to a decrease in the sintering temperature from 1400 to 1100 oC, which can result in the reduction of SOFC fabrication costs. For the GDC powder with 0.25 mol% Cu additive, linear shrinkage rates over the range of 1100 to 1400 oC were the highest (ca. 16.79-17.34 %). Regarding ionic conductivity, the 0.25 and 0.5 mol% Cu-added samples showed a higher value than the untreated GDC powder in the range of 550 to 750 oC, while the value for the 0.75 mol% Cu-added sample was lower. This result was evidenced by the occurrence of mechanical defects in body of the GDC samples with higher Cu contents (≥ 0.75 mol%). In addition, the activation energy of the CuO-GDC prepared in this work remained unchanged significantly. These results obtained in this study suggest that further investigations of proper sintering aids with the combination of different metal oxides and the optimization of GDC-electrolyte synthesis conditions may enable more stable and efficient SOFCs based on GDC. Figure 1

Low temperature synthesis of novel SrCe0.9Yb0.1O3−α-chlorides composite electrolytes for intermediate temperature protonic ceramics fuel cells

In this study, novel SrCe0.9Yb0.1O3−α-(Na/K)Cl and SrCe0.9Yb0.1O3−α-NaCl-BaCl2 composite electrolytes were synthesized at low temperature (750°C). The structural properties of the composite electrolytes based on mixtures of SrCe0.9Yb0.1O3−α (SCY) and chlorides ((Na/K)Cl, NaCl-BaCl2) are characterized. The microstructure of the composite electrolytes are observed by scanning electron microscopy (SEM). The electrical conductivity is determined by impedance spectroscopy. The ionic conductivities of the composite electrolytes are higher than that of SCY. Finally, high-performance intermediate temperature fuel cells of the composite electrolytes are obtained.

Three-dimensional Inkjet Printed Solid Oxide Electrochemical Reactors. I. Yttria-stabilized Zirconia Electrolyte

Solid oxide fuel cell (SOFC) and electrolyser (SOE) performances can be enhanced significantly by increasing the densities of (electrode | electrolyte | pore) triple phase boundaries and improving geometric reproducibility and control over composite electrode | electrolyte microstructures, thereby also aiding predictive performance modelling. We developed stable aqueous colloidal dispersions of yttria-stabilized zirconia (YSZ), a common SOFC electrolyte material, and used them to fabricate 2D planar and highly-customisable 3D microstructures by inkjet printing. The effects of solids fraction, particle size, and binder concentration on structures were investigated, and crack-free, non-porous electrolyte planes were obtained by tailoring particle size and minimising binder concentration. Micro-pillar arrays and square lattices were printed with the optimised ink composition, and a minimum feature size of 35μm was achieved in sintered structures, the smallest published to-date. YSZ particles were printed and sintered to a 23μm thick planar electrolyte in a Ni-YSZ|YSZ|YSZ-LSM|LSM electrolyser for CO2 splitting; a feed of 9:1 CO2:CO mixture at 1.5V and 809°C produced a current density of −0.78 A cm−2 even without more complex 3D electrode | electrolyte geometries.

Effect of Ca2+ and Sr2+ doping on the microstructure and cell performance of samaria-doped ceria electrolytes used in solid oxide fuel cells

Ce0.8Sm0.15Ca0.05O1.875 (S15C05DC) and Ce0.8Sm0.15Sr0.05O1.875 (S15S05DC) electrolytes were synthesized by a solid-state reaction and used to prepare solid oxide fuel cells. The microstructures and electrical properties of the electrolytes were analyzed by XRD, SEM, thermal analyzer, thermomechanical analysis, TEM, electrochemical analysis, and impedance spectroscopy. The maximum densification strain rates of S15C05DC and S15S05DC were 10.6 × 10−3–11.1 × 10−3 min−1 at 1330 °C and 8.3 × 10−3–8.7 × 10−3 min−1 at 1300 °C, respectively. The addition of Ca2+ or Sr2+ could help in accelerating CeO2 sintering. The maximum open-circuit voltages and power densities of La0.6Sr0.4Co0.2Fe0.8O3−δ/S15C05DC/Ce0.8Sm0.2O1.9-Ni (cell I) and La0.6Sr0.4Co0.2Fe0.8O3−δ/S15S05DC/Ce0.8Sm0.2O1.9-Ni (cell II) were 0.72 V and 213 mW cm−2 and 0.71 V and 173 mW cm−2, respectively, at 800 °C. The ohmic resistances of cells I and II are 0.443 and 0.505 Ω cm2, respectively, at 800 °C. The conclusion is that S15C05DC is a better choice than S15S05DC in the electrolyte materials.

Ceramic Polymer Hybrid Electrolyte Based on Li7La3Zr2O12 for Solid-State Batteries

Solid-state lithium-ion batteries are a promising type of batteries for future applications. While replacing flammable liquid electrolytes with solid alternatives gives advantage to improved safety, the higher density of these solids compared to the currently used liquids is detrimental to the gravimetric energy density. Therefore, for sufficient battery cell performance thin and dense electrolyte layers of highly Li+ conductive material are needed. Currently, materials investigated for solid electrolyte application include ceramics, glasses and polymers. Ceramic Li7La3Zr2O12 (LLZO) with cubic garnet like crystal structure has emerged as one of the most promising materials as electrolyte. Its advantages include high Li+ conductivity and chemical stability vs. lithium metal anodes. The material can be synthesised by solid state reactions as well as various wet chemistry routes. The product usually obtained from all methods is a powder. Processing this powder into a thin electrolyte layer that is suitable for battery production proofs to be difficult. Physical vapour deposition methods (e.g. pulsed laser deposition or sputtering) have been used to create thin film layers of LLZO, but these methods are limited and not suitable for large scale production. Easier processing techniques (e.g. tape casting and extrusion) are found for solid polymer electrolytes, but so far ionic conductivities of solid polymer electrolytes fall short of ceramic and glass electrolytes. The objective of this study is to combine the advantages of ceramic and polymer electrolytes by fabrication of a hybrid solid state electrolyte. The hybrid mainly consists of LLZO and employs a polymer electrolyte as a binder. The aim is to produce a hybrid electrolyte for easier processing of solid-state batteries. Therefore, LLZO powder obtained from a facile wet chemistry synthesis route is mixed with solid polymer electrolyte. Thin hybrid electrolyte membranes are obtained using the tape casting method. Ceramic content of the hybrid electrolyte is varied up to 80-wt %. Both LLZO powders and the hybrid electrolytes are characterized in regard to structure and electrochemical performance. Phase composition and crystal structure of the prepared powder are checked using X-ray diffraction (XRD). Morphology of powders and microstructure of the hybrid electrolytes are investigated with scanning electron microscopy (SEM). Thermal behavior of the hybrid electrolytes is examined using differential scanning calorimetry (DSC). Electrochemical impedance spectroscopy (EIS) is used to evaluate the ionic conductivity and special attention is paid to the ceramic polymer interaction. Its influence on lithium ion transport is discussed in detail. We show that the combination of LLZO with polymer greatly simplifies the production of thin solid state electrolytes for lithium-ion batteries with only small losses in conductivity.

Microstructure and electrical properties of solid electrolytes of fully stabilized zirconia with rare earth mixed oxides

<p>In this work was obtained solid electrolytes of fully stabilized zircônia with doped of 10 and 12 mol% of <em>Re<sub>2</sub>O<sub>3</sub></em> (mixed oxides rare earth), for use in oxygen sensors and or fuel cells. The specimens were prepared by uniaxial pressing and sintered using two heating schedules, <em>S1</em> and <em>S2</em>. Impedance diagrams show that the crystalline phases and the grain size change the electrical behavior of the ceramics. The sample with the best electrical performance was obtained with 10 mol% doped and was sintered with the curve S1. The value of the total conductivity of this sample was 2,85x10<sup>-3</sup> <span style="font-family: Symbol;">W</span><sup>-1</sup>.cm<sup>-1</sup> (taken at 600 ° C). When making a comparison between this values of conductivity with the reported in the literature is identified similarity with or traditional system zirconia-yttria the most widely used commercially as electrolyte oxygen sensors and fuel cells, confirming the potential use of the oxides mixed rare earth for these specific applications.</p>

Phosphate Based Ceramics As Solid Electrolyte for High Temperature Lithium Ion Batteries

A Li-ion battery with liquid electrolyte may suffer from security risks such as inflaming or short circuits. A solid electrolyte made of ion conducting glass-ceramic is thermally more stable. If the ion conducting ceramics as combined electrolyte and separator could be used in a battery, the battery will be safer. LAGP (Li1+x AlxGe2-x (PO4)3) was investigated as a candidate for solid electrolytes in Li ion batteries. LAGP glass samples were produced using the melt-quench-method. Samples were fabricated using powder compaction by sintering or by direct heat treatment of the glass. Their ionic conductivities were measured with impedance spectroscopy. Dilatometer measurements, X-ray diffraction and scanning electron microscope analysis were also carried out. The thermal properties like crystallization temperature, heat capacity and thermal conductivity were measured with differential scanning calorimeter and Laser-Flash apparatus. Multiple batches of LAGP with different composition were produced. The ionic conductivity of 3·10-4 S/cm at room temperature and 1·10-2 S/cm at 150°C was achieved. The relationship between the process parameters, the microstructure and ionic conductivity of the solid electrolyte was studied. Also, their influence on the heat capacity and the thermal conductivity was studied. All-solid test cells were fabricated using LAGP ceramic as solid electrolyte. Magnetron sputtering, spark plasma sintering and furnace sintering were used to produce the anode-electrolyte-cathode multilayer tablets. The tablets were assembled in swagelok-cells and tested between 100°C and 200°C.

Investigation of micro-tube solid oxide fuel cell fabrication using extrusion method

Extrusion is one of the most effective and inexpensive methods used in the production of ceramic tubes for tubular or micro-tubular solid oxide fuel cell (SOFC) applications. In this method, the parameters such as the viscosity of the ceramic slurry, the extrusion speed and the die temperature need to be optimized for a high performance. In this study, anode supported micro-tubular solid oxide fuel cells are successfully fabricated via a specially designed vertical-type piston extruder machine. The die design enables the production of micro-tubular SOFCs with outer diameters from 3 to 4.5 mm. The die temperature is determined to be the most important process parameter and the suitable die temperature is ranging 40–70 °C depending on the slurry content. The electrolyte layer is coated on the anode support tube by vacuum assist dip coating technique and co-sintering is applied with a home-made porous sintering apparatus to avoid dimensional anomalies. The effects of the parameters such as the composition of the electrolyte solution, the vacuum pressure and the immersion time on the electrolyte thickness are investigated. It is found that the electrolyte thickness decreases when the immersion time and vacuum pressure are reduced. Moreover, the thickness of the electrolyte is found to be depended on the content of the electrolyte solution. The effect of the pre-sintering temperature on the electrolyte quality is also investigated. The sintering temperatures of 1000 °C and 1100 °C provide a similar and desired electrolyte microstructure. A peak power density of 140 mW cm−2 is obtained at 700 °C from the final cell.

Dominant Factors Influencing the Electrochemical Performance of Plasma-Sprayed LSGM Electrolyte

Mg/Sr-doped lanthanum gallate (LSGM) is one of promising electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) because of its high ionic conductivity. However, a main challenge in the application of LSGM is how to fabricate dense and thin LSGM electrolytes on electrode substrates at relatively low temperature since it is difficult to sinter LSGM to full density below 1500 °C. In this study, low-cost atmospheric plasma spraying (APS) is used to fabricate the thin and dense LSGM electrolyte. The effects of deposition temperature and particle size on the phase composition, microstructure, and electrochemical performance of LSGM electrolyte were investigated. It was found that the deposited LSGM presents a dense microstructure with well bonded lamellar interfaces with a porosity of ~2.3% when the deposition temperature is >300°C. Besides, the electrochemical performance depends sensitively on the particle size of LSGM powders because Gallium (Ga) may evaporate during plasma spraying. It was revealed that when the particle size is <30 μm, Ga evaporation loss increases rapidly with the decrease of particle size, which dramatically reduces the ionic conductivity of the LSGM deposits. The ionic conductivity of a dense LSGM deposit was only ~4.2% of the bulk conductivity. It was found that using LSGM powders with particle sizes >30 μm, plasma-sprayed LSGM reaches an ionic conductivity of ~0.075 S cm-1 at 800 °C, ~78% of the bulk value. Test cells based on the plasma-sprayed LSGM electrolyte show excellent performance. At 800°C, a maximum output power density of over 700W/cm2 was obtained with a APS ~60um thick LSGM under test condition of H 2 /Air, indicating that atmospheric plasma spraying is a promising approach for large-scale manufacturing of high-performance IT-SOFCs.

Advanced Impedance Spectroscopy Study of the Influence of the Crystalline Structure on the Ionic Conduction of Thin Solid-State Electrolytes

Solid electrolytes exhibit electrical conductivity due to the presence of mobile ions which act as charge carriers through the crystalline structure. For their use in solid oxide fuel cells (SOFCs), a sufficient electrical conductivity is achieved by operating at high temperatures. To reduce the application temperature, research is dedicated to increase the electrical conductivity of the ceramic material otherwise. One way is decreasing the film thickness. Yet, the relationship between the material crystallinity and the ion conductivity may be reinterpreted when reducing the thickness to the micrometer and nanometer scales. Another way is by reducing the grain size. At present it is not clear how the microstructure of solid state electrolytes affect the electrical conduction. In literature, the experiments on nanocrystalline solid oxides yield contradictory observations [1-6]. A good understanding of the relationship between microstructure and ion conductivity would open the possibility to engineer advanced thin materials for solid oxide fuel cells. We propose an experimental and modeling approach that aims at unraveling the electrical behavior of thin film solid state electrolytes, by considering the crystalline nature of the material. Through careful comparison of simulations and measurements we want to explain the observed electrical properties of these materials to predict how their conductivity can be enhanced. In this research, the complex electrical properties at different temperatures of yttrium-doped ceria electrolytes, with different thicknesses and grain sizes, are determined by electrochemical impedance spectroscopy (EIS). The solid oxide is deposited by reactive magnetron sputtering, which allows us to modify the morphology and composition of the thin film in a controlled and flexible way [7]. In the EIS characterization, improved electrode geometry is also searched. Experiments with platinum co-planar electrodes are performed and compared with those with an interdigital electrode structure. The specific electrode geometry is designed by 2D simulations for a solid oxide film in contact with the substrate. A finite element model of the electrical conductivity was recently developed to simulate impedance spectra and electrical conductivities as a function of grain size and temperature [8]. More rigorous than the dilute solution models, it is based on the application of the linear phenomenological relations to a crystal lattice. The impedance modeling provides a description of the electrical behavior of the material. The EIS results are then compared with the ones generated by the finite element model. The combined analysis aims to elucidate the experimental evidence that is not explained by the available physical models. Therefore, it represents a strong approach to understand the electrical properties and ion conduction of solid electrolytes. [1] J. Maier “Ionic conduction in space charge regions”, Progress in Solid State Chemistry 23 (1995) 171–263. [2] J. Maier “Nano-sized mixed conductors (Aspects of nano-ionics. Part III)”, Solid State Ionics 148 (2002) 367–374. [3] X. Guo, R. Waser “Electrical properties of the grain boundaries of oxygen ion conductors: Acceptor-doped zirconia and ceria”, Progress in Materials Science 51 (2006) 151–210. [4] J. Maier “Nanoionics: ionic charge carriers in small systems”, Physical Chemistry Chemical Physics 11 (2009) 3011–3022. [5] C. Peters, A. Weber, B. Butz, D. Gerthsen, E. Ivers-Tiffée “Grain-Size Effects in YSZ Thin-Film Electrolytes”, Journal of the American Ceramic Society 92 (9) (2009) 2017–2024. [6] X. Guo “Can we achieve significantly higher ionic conductivity in nanostructured zirconia?”, Scripta Materialia 65 (2011) 96–101. [7] S. Mahieu, P. Ghekiere, G. De Winter, S. Heirwegh, D. Depla, R. De Gryse., O.I. Lebedev, G. Van Tendeloo “Mechanism of preferential orientation in sputter deposited titanium nitride and yttria-stabilized zirconia layers”, Journal Of Crystal Growth 279 (1-2) (2005) 100-109. [8] D. Van Laethem, A. Hubin, J. Deconinck “Finite element modelling of the electrical conductivity of acceptor doped ceria”, 6th International Conference on Fundamentals and Development of Fuel Cells, 3rd- 5th February, Toulouse (France).

Fabrication and Microstructure of Self-Supporting Thin Ceramic Electrolytes Prepared by Laser Machining

Alternatively to electrode-supported configurations, electrolyte-supported solid oxide fuel cells (SOFC) are preferred in terms of mechanical robustness and resistance to redox cycles. However, the main inconvenience of this design is that electrolyte supported cells are prepared over 100–300 µm thick electrolytes and, as a consequence, they are designed to operate at high temperatures to reduce its ohmic resistance. The typical operation temperature of electrolyte supported SOFC is about 900 ºC for yttria-stabilised zirconium oxide (YSZ) electrolytes. A different alternative is to use laser machining to prepare thin self-supporting ionic conducting membranes. These membranes are obtained by laser machining of a thick and sintered ceramic plate. They consist of a thin central region, which is the electrochemically active area, surrounded by a thick zone, which acts as mechanical support. As both parts come from the same original sintered plate, they have unbeatable thermomechanical integration. Laser engraving is being reported in the last few years as a very suitable technique for achieving cost-efficient production of high quality ceramic parts. It allows obtaining excellent shaping, versatility, accuracy and highly controlled surface finishing if compared with conventional abrasive techniques for ceramic machining. Using a commercial equipment that consists mainly of a λ=532 nm laser source and a galvanometric-controlled head, we have demonstrated that laser ablation within the nanosecond regime can engrave the surface of a conventional 150 μm thick 8YSZ plate (8 mol% Y2O3) by getting circular thin areas up to 20 μm in thickness and 8 mm in diameter. The membranes do not show problems of cracking due to thermal cycles in the final piece. The thickness and surface quality has been characterised by confocal optical profilometry. Electron BackScattering Diffraction (EBSD) technique has been used to determine the in-depth profile of the residual strains produced by the laser machining. Within the accuracy of the technique used, most of the laser damage is limited to the first layer of YSZ grains, i.e. to the 2-5 µm most superficial membrane layer. Transmission Electron Microscopy (TEM), combining electron diffraction and Energy Dispersive Spectroscopy (EDS), has also been used to characterise melted particle ejection during the ablation process, as well as the mechanisms of resolidification and redeposition on the surface. These experiments confirm that laser debris redeposited over the membrane surface is mainly formed by nanometric particles with the same composition and crystalline phase as the 8YSZ original plate. Thus, this debris is not detrimental for obtaining a good electrolyte-electrode contact, but would also improve the electrochemical contact by increasing the electrolyte surface roughness. Fig. 1.- Image of a laser-machined 8YSZ ceramic membrane. Fig. 2.- TEM image and electron diffraction pattern of nanometric particles produced by the laser ablation of a 8YSZ ceramic plate. Fig. 3.- Cross-section of a 8YSZ laser-processed ceramic plate. (a) EBSD crystallographic orientation map. (b) Local misorientation map. Figure 1

Effects of surface chemistry and microstructure of electrolyte on oxygen reduction kinetics of solid oxide fuel cells

We report systematic investigation of the surface properties of yttria-stabilized zirconia (YSZ) electrolytes with the control of the grain boundary (GB) density at the surface, and its effects on electrochemical activities. The GB density of thin surface layers deposited on single crystal YSZ substrates is controlled by changing the annealing temperature (750–1450 °C). Higher oxygen reduction reactions (ORR) kinetics is observed in samples annealed at lower temperatures. The higher ORR activity is ascribed to the higher GB density at the YSZ surface where ‘mobile’ oxide ion vacancies are more populated. Meanwhile, oxide ion vacancies concurrently created with yttrium segregation at the surface at the higher annealing temperature are considered inactive to oxygen incorporation reactions. Our results provide additional insight into the interplay between the surface chemistry, microstructures, and electrochemical activity. They potentially provide important guidelines for engineering the electrolyte–electrode interfaces of solid oxide fuel cells for higher electrochemical performance.

Fabrication and Microstructure of Self-Supporting Thin Ceramic Electrolytes Prepared by Laser Machining

Self-supporting thin Yttria Stabilized Zirconia (YSZ) ceramics electrolytes have been prepared by laser machining. They are carved from a sintered YSZ plate to shape a 20 µm thick and 8 mm in diameter central region, surrounded by an unprocessed 150 µm thick supporting zone. Scanning Electron Microscopy (SEM) and Electron BackScattering Diffraction (EBSD) studies confirmed that the strains produced by the laser processing are small and limited to only one or two layers of YSZ grains (~5 µm). SEM and Transmission Electron Microscopy (TEM) have been also used to characterize the surface of the membrane. It is corrugated and coated with YSZ nanoparticles as a result of the laser plasma deposition. Electrochemical characterization by Impedance Spectroscopy (EIS) showed that this surface morphology improves the electrical performance of the membrane slightly but clearly, reducing the cathode polarization resistance by about 5% in the 650-850 ºC range.

Preparation and characterization of LSO-SDC composite electrolytes

The properties of LSO-SDC composite electrolytes prepared by the mixed powder with different LSO/SDC mass ratios were studied. The apatite-type lanthanum silicates La10Si6O27 (LSO) and Sm0.2Ce0.8O1.9 (SDC) were synthesized via sol-gel process and glycine-nitrate process (GNP), respectively. The phase structure, microstructure, relative density, thermal expansion properties and oxygen ion conductivity of the samples were investigated by means of techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, dilatometer, and AC impedance spectroscopy. The results showed that SDC addition to the samples could enhance the density of the samples. However, the LSO-SDC composite electrolyte sintered at 1550 °C was over sintering when the SDC content was 50 wt.%. At the lower content of SDC (0−10 wt.%), the decrease of conductivity was predominantly attributed to the reducing concentration of carriers. However, the conductivities of the composite electrolytes increased with the increasing SDC content (10 wt.%−40 wt.%) because of the enhanced percolation of highly conductive SDC component in the microstructure of composite electrolytes. In addition, the dependence of conductivity on p(O2) showed that LSO-SDC composite electrolytes were stable in the examined range of p(O2).

Structural and electrical properties of BaCe0.9Ee0.1O2.95 electrolyte for IT-SOFCs

BaCe0.9Ee0.1O2.95 (BCE) nanopowder was synthesized by citric-nitric autocombustion method. Rietveld refinement analysis showed that unit cell volume was slightly larger compared with the most known BaCe0.9Y0.1O2.95, which might contribute to higher proton mobility. Sinterability of BaCeO3 is also enhanced by doping with Eu, since dense single-phased BCE electrolyte microstructure comprising of 1–2μm grains was obtained after sintering at 1450°C for 5h. The electrochemical impedance spectroscopy (EIS) analysis revealed separate bulk and grain boundary contributions to the total electrolyte conductivity below 200°C. The grain boundary conductivity was one to two orders of magnitude lower than the bulk conductivity, indicating blocking effect of the grain boundaries to the mobility of charge carriers. This effect diminished completely above 500°C and only total conductivities were determined between 500 and 700°C. Conductivity of BCE in a wet hydrogen atmosphere at 600°C reached 1.2×10−2S/cm, which can be considered as one of the highest conductivities among BaCeO3 based proton conductors.

Anode supported single chamber solid oxide fuel cells operating in exhaust gases of thermal engine

This project deals with the development and the electrochemical characterization of anode supported single chamber SOFC in a simulated environment of thermal engine exhaust gas. In the present work, a gas mixture representative of exhaust conditions is selected. It is composed of hydrocarbons (HC: propane and propene), oxygen, carbon monoxide, carbon dioxide, hydrogen and water. Only oxygen content is varied leading to different gas mixtures characterized by three ratios R = HC/O2. Concerning the cell components, a cermet made of nickel and an electrolyte material, Ce0.9Gd0.1O1.95 (CGO) is used as anode and two cathode materials, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and Pr2NiO4+δ (PNO), are evaluated. The prepared cells are investigated in the various gas mixtures for temperatures ranging from 450 °C to 600 °C. Ni-CGO/CGO/LSCF-CGO cell has delivered a maximum power density of 15 mW cm−2 at 500 °C with R = HC/O2 = 0.21, while lower power densities are obtained for the other ratios, R = 0.44 and R = 0.67. Afterwards, LSCF and PNO cathode materials are compared and LSCF is found to deliver the highest power densities. Finally, by improving the electrolyte microstructure, some cells presenting a maximum power density of 25 mW cm−2 at 550 °C are produced. Moreover, up to 17% of initial HC are eliminated in the gas mixture.

Plasma-Sprayed Y2O3-Stabilized ZrO2 Electrolyte With Improved Interlamellar Bonding for Direct Application to Solid Oxide Fuel Cells

Atmospheric plasma spraying was employed to prepare anode, cathode, and Y2O3-stabilized ZrO2 (YSZ) electrolyte to aim at reducing manufacturing cost. YSZ electrolytes were deposited on the anode at different deposition temperatures of 200 °C, 400 °C and 600 °C to optimize the gas tightness of plasma-sprayed YSZ electrolyte. The influences of the deposition temperature on the microstructure and gas-tightness of plasma-sprayed YSZ electrolyte were investigated. The effect of microstructure and the gas-tightness of YSZ electrolyte on the open circuit voltage and the output performance of solid oxide fuel cells (SOFCs) were examined. The results showed with the increase of deposition temperature, the porosity of YSZ electrolytes almost decreased by about 80% and the microstructure of YSZ electrolytes changed from the typical lamellar structure to the continuous columnar crystal structure. At a deposition temperature of 600 °C the gas permeability decreased to 1.5 × 10−7 cm4gf−1s−1, and the highest open circuit voltage can reach 1.026 V, indicating the applicability of the as-sprayed YSZ directly to the SOFC electrolyte.