SOFC Electrolyte Research Articles

Deformation and Fracture Characteristics of Zirconia and Ceria-Based Electrolytes for SOFCs under Reducing Atmospheres

In this paper, we discuss the effects of different oxygen partial pressures on the elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC). The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 åC under different oxygen partial pressures in the range of 0.2 to 10-22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10-15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ.

Investigation of High Temperature Elastic Modulus and Internal Friction of SOFC Electrolytes Using Resonance Method

The Young's modulus, the shear modulus, the Poisson ratio and the internal friction of typical electrolyte materials for SOFC, (Gd2O3)0.05(CeO2)0.9, (Sm2O3)0.05(CeO2)0.9, (Y2O3)0.08(ZrO2)0.92, (Y2O3)0.1(ZrO2)0.9, (Sc2O3)0.1(ZrO2)0.9, (Sc2O3)0.9Ce0.01(ZrO2)0.89 were evaluated by a resonance method. The measurements were carried out from room temperature to 1273 K in flowing pure Ar. The Young's modulus of (Gd2O3)0.05(CeO2)0.9 and (Sm2O3)0.05(CeO2)0.9 gradually decreased with increasing temperature as expected for the typical ceramics. However, the Young's modulus of the series of zirconia drastically decreased in the temperature range between 573 K and 873 K, and correspondingly the internal friction increased. Such a characteristic temperature dependence of the mechanical properties was discussed in terms of phase change.

Performance of a New Cu-Ceria Based Anode for SOFCs Running on Different Fuels

A new Cu-ceria based material was evaluated as the anode for SOFC. Physicochemical characterisation, electrical properties in reducing atmosphere as well as thermal and chemical compatibility with common SOFC electrolytes were first investigated. A single cell with 8YSZ electrolyte and this anode material was prepared and tested in H2 and methane fuels at 1023 K, using air as oxidant. Cell was running for more than 340 h and demonstrated the ability of utilise not only hydrogen but also methane as fuel. The results suggest that material under study can be considering as anode for SOFC operating with hydrogen or hydrocarbons. Cell performance could be improved by optimising the cell fabrication method as well as using an appropriate electrolyte and cathode material to operate at this relative low temperature, such us doped ceria and perovskites respectively.

Improvement of Micro Tubular SOFCs using Multi-Layered Electrolyte

Fabrication technology of multi-layered electrolyte for micro tubular SOFCs has been developed. Sc2O3 stabilized ZrO2(ScSZ) and Gd2O3-doped CeO2 (GDC) was selected for the electrolyte materials and a GDC-ScSZ-GDC multi-layered electrolyte was successfully prepared using multiple dip coating and co-firing technique. The thickness of each layer for the electrolyte was about 3, 3, and 12 micron, respectively. The cell performance test showed the open circuit voltage (OCV) of over 1 V at 600oC or higher, while a SOFC with 10 micron thick GDC electrolyte showed the OCV of 0.78 V at 600oC. The cell performance of 0.35 Wcm-2 @ 0.7 V was obtained at the operating temperature of 650 oC.

Effects of cobalt metal addition on sintering and ionic conductivity of Sm(Y)-doped ceria solid electrolyte for SOFC

The effects of cobalt addition (0.5 and 1 wt.%) on densification and ionic conductivity of Ce 0.9Sm 0.1O 1.95 (10SDC) and Ce 0.9Sm 0.075Y 0.025O 1.95 (2.5Y-SDC) have been studied. X-ray diffraction (XRD) showed that Co had changed to Co 3O 4 and Co 3O 4 + CoO after firing at 900 °C and 1300 °C respectively. The addition of Co promoted densification to occur at lower temperatures with a more uniform grain growth and greatly improved both grain boundary and bulk conductivity for 10SDC. Significant improvement of grain boundary for the 2.5Y-SDC samples was obtained, even at 1300 °C sintering, while bulk conductivity was slightly improved. Rapid grain growth along with improvement of ionic conductivity was observed when the samples were sintered further at higher temperature. Superior ionic conductivity of the 2.5Y-SDC samples with Co addition to that of the bare 10SDC suggested the potential use of Co as the co-dopant in this system to reduce the content of costly rare earth usage.

Performance of ionic-conducting ceramic/carbonate composite material as solid oxide fuel cell electrolyte and CO 2 permeation membrane

Novel composite materials composed of an oxygen ionic-conducting ceramic oxide and a molten carbonate phase have recently been reported to be the promising materials for the electrolyte of intermedaite temperature (500–700 °C) solid oxide fuel cell (ITSOFC) and the membrane for high temperature (>500 °C) CO 2 separation. This work reviews the recent progresses of these composite materials as ITSOFCs electrolyte and CO 2 permeation membrane and reports the latest results of our group. The composite materials, i.e., samarium-doped ceria (SDC)–Li/Na/K 2CO 3 (43.5/31.5/25 mol%) and SDC–Li/Na 2CO 3 (50/50 mol%), were prepared and tested as the electrolyte for SOFCs, respectively. The CO 2 in the cathode gas enhances the power output. At 650 °C, and with CO 2/O 2 used as the cathode gas, the fuel cell with SDC–Li/Na 2CO 3 (50/50 mol%) electrolyte gives a power output 1700 mW cm −2 at a current density 3000 mA cm −2. Another composite material made of Bi 1.5Y 0.3Sm 0.2O 3/molten carbonate (Li/Na/K 2CO 3, 43.5/31.5/25 mol%) was synthesized and used for selective permeation of CO 2 at 500–650 °C. The CO 2 permeation flux for the dual-phase membrane increases with the increase of temperature and reaches a maximum value of 6.60 × 10 −2 mL cm −2 min −1 at 650 °C, with apparent activation energy for CO 2 permeation of 113.4 kJ mol −1. These results further demonstrate that the ionic-conducting ceramic/carbonate composite material is an alternative choice as the ITSOFCs electrolyte and high temperature CO 2 separation membrane material. The ionic transfer mechanism is discussed.

Mechanically activated self-propagating high-temperature synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ as an electrolyte for SOFC

In this paper, we report on synthesis of highly pure La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ (LSGM9182) powder with high crystallinity by mechanically activated (MA) self-propagating high-temperature synthesis (SHS), in which the synergy effects of MA and SHS on final and intermediate products were mainly examined. In the experiments, raw materials of La 2O 3, SrCO 3, Ga 2O 3, Mg and NaClO 4 were fractured and well mixed by planetary ball milling for different periods from 0 h to 24 h, then the bottom surface of the green compacts were electrically ignited for producing pure LSGM9182 through the propagation of sustainable exothermic reaction. The final and intermediate products, shortly after MA treatment, were characterized by XRD, SEM, XRF and particle size analyzer. During the planetary ball milling, the raw materials became gradually amorphous due to disordering of crystal structure. Interestingly, the longer milling operation caused the larger particle size of the raw material because nanoparticles, generated by the milling, became easily massed together. More significantly, the MA pretreatment improved a reactivity of the SHS to purify the product. In particular, the combination of MA–SHS with ball milling of 24 h at 300 rpm gave the highest-grade LSGM9182 product of nano-sized primary particles. The results appealed that the SHS after the MA treatment was quite effective for initiating, activating, sustaining and completing the solid–solid reaction synthesis of functional perovskite-type oxide with mild exothermic heat.

Non-Ionic Conduction Phenomena in Yttria Stabilized Zirconia Electrolyte in SOFC Operated in the Electrolysis Mode

not Available.

Structural Stability of GDC Electrolyte for Low-Temperature SOFCs Depending on Fuels

not Available.

Deformation and Fracture Characteristics of Zirconia and Ceria-Based Electrolytes for SOFCs under Reducing Atmospheres

not Available.

Investigation of High Temperature Elastic Modulus and Internal Friction of SOFC Electrolytes Using Resonance Method

not Available.

Thermal stability study of SDC/Na 2CO 3 nanocomposite electrolyte for low-temperature SOFCs

The novel core–shell nanostructured SDC/Na 2CO 3 composite has been demonstrated as a promising electrolyte material for low-temperature SOFCs. However, as a nanostructured material, stability might be doubted under elevated temperature due to their high surface energy. So in order to study the thermal stability of SDC/Na 2CO 3 nanocomposite, XRD, BET, SEM and TGA characterizations were carried on after annealing samples at various temperatures. Crystallite sizes, BET surface areas, and SEM results indicated that the SDC/Na 2CO 3 nanocomposite possesses better thermal stability on nanostructure than pure SDC till 700 °C. TGA analysis verified that Na 2CO 3 phase exists steadily in the SDC/Na 2CO 3 composite. The performance and durability of SOFCs based on SDC/Na 2CO 3 electrolyte were also investigated. The cell delivered a maximum power density of 0.78 W cm −2 at 550 °C and a steady output of about 0.62 W cm −2 over 12 h operation. The high performances together with notable thermal stability make the SDC/Na 2CO 3 nanocomposite as a potential electrolyte material for long-term SOFCs that operate at 500–600 °C.

The chemical stability and conductivity of BaCe 0.9− xY xNb 0.1O 3− σ proton-conductive electrolyte for SOFC

BaCe 0.8Y 0.2O 3− δ and BaCe 0.9− x Y x Nb 0.1O 3− δ ( x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.35) were prepared by a solid-state reactions. It was found that the BaCe 0.8Y 0.2O 3− δ samples decomposed into CeO 2 and BaCO 3 after being exposed in the atmosphere (3% CO 2 + 3% H 2O + 94% N 2) at 700 °C for 10 h. However, samples containing Nb remains unchanged in the same conditions, demonstrating a better stability in the presence of CO 2 and H 2O. The conductivity of BaCe 0.9− x Y x Nb 0.1O 3− δ increased with the increase of Y content ( x ≤ 0.30), and the highest value was observed at x = 0.30 where a significant decrease in conductivity took place at x = 0.35. The conductivity of BaCe 0.6Y 0.3Nb 0.1O 3− δ reaches 0.01 S/cm in humid hydrogen at 700 °C, slight lower than BaCe 0.8Y 0.2O 3− δ , 0.012 S/cm in the same conditions. Fuel cell with BaCe 0.6Y 0.3Nb 0.1O 3− δ as-prepared was successfully prepared and humidified hydrogen was supplied as fuels in evaluating the fuel cell performance. The open circuit voltage, peak power density and interfacial resistance at 700 °C were 1.02 V, 345 mW/cm 2 and 0.27 Ω cm 2, respectively.

Fabrication of 8-YSZ thin-wall tubes by powder extrusion moulding for SOFC electrolytes

In this work the processing steps for producing YSZ thin tubes by means of powder extrusion moulding (PEM) technique are investigated. Different feedstocks were prepared from a commercial YSZ powder and a multicomponent thermoplastic binder system based in polypropylene and paraffin wax. The surface coating of YSZ powder with stearic acid in a high-performance dispersing instrument reduces the viscosity of the feedstock one order of magnitude respect to a feedstock with a same composition and un-coated powder. This fact allows increasing the solid loading up to 58 vol.% to obtain sintering tubes with densities higher than 97% and with wall thickness lower than 200 μm.

J0601-1-3 固体酸化物形燃料電池の電解質特性に及ぼす原料粉末中の水分の影響(SOFC内の電極近傍現象)

J0601-1-3 固体酸化物形燃料電池の電解質特性に及ぼす原料粉末中の水分の影響(SOFC内の電極近傍現象)

Development of anode material based on La-substituted SrTiO 3 perovskites doped with manganese and/or gallium for SOFC

Materials based on La-substituted SrTiO 3 perovskites doped with manganese and/or gallium for SOFC have been studied as novel anodes for solid oxide fuel cell. La 4Sr 8Ti 11Mn 1− x Ga x O 38− δ (0 ≤ x ≤ 1) oxides were synthesized by solid state reaction and the influences of the manganese and/or gallium content on the structure, morphology, thermal properties and electrical conductivity of these materials has been investigated. All compounds show cubic structure with a space group Pm-3m. These compounds presented high electrical conductivity values under reducing atmosphere between 7.9 and 6.8 S cm −1 at 900 °C. For the composition x ≥ 0.5, the thermal expansion coefficient in both reducing and oxidizing atmosphere are close to that of SOFC electrolytes (8YSZ, CGD). In general, the substitution of Ga by Mn causes a slight reduction in each of the following, lattice parameter, degree of oxygen loss on reduction, thermal expansion coefficient, and electrical conductivity.

Optimization of the Processing of 8‐YSZ Powder by Powder Injection Molding for SOFC Electrolytes

The development of a new multicomponent thermoplastic binder system for injection molding of yttria‐stabilized zirconia (8‐YSZ) bars based in polypropylene and paraffin wax (PW) is presented in this paper. The surface coating of YSZ powder with stearic acid in a high‐performance dispersing instrument reduced the viscosity of the feedstock by one order of magnitude with respect to a feedstock with the same composition and uncoated powder. This fact allowed us to obtain a feedstock with a viscosity curve more suitable for the injection process without requiring high proportions of PW in the binder composition. The density of the samples was >98% and the conductivity of sintered parts are comparable to those of samples uniaxially compacted, around 0.10 S/cm at 900°C.

Substrate effect on the electrical properties of sputtered YSZ thin films for co-planar SOFC applications

The physical and electrical properties of sputtered YSZ thin films on various substrates were investigated. The in-plane electrical properties of the films were measured for evaluating YSZ thin film for co-planar SOFC electrolytes. The conductance measured on YSZ over Si substrates was significantly affected by the buffer layer thickness and exhibited higher values than that of YSZ on sapphire. This indicates that electrical leakage occurred through the substrate when Si substrates were utilized. Nevertheless, pure ionic conduction was observed in YSZ/sapphire regardless of the film thickness. It implies that much care should be taken for the selection of substrate materials in measuring or utilizing in-plane conductivity, especially for high temperature applications.

Efeito de íons aliovalentes nas propriedades elétricas de céria dopada com ítria

A alta temperatura de operação da PaCOS pode causar a formação de fases resistivas isolantes na interface eletrólito-catodo o que contribui para a perda de eficiência da pilha, podendo-se citar como exemplo a formação de zirconatos na interface manganita de lantânio dopada com estrôncio (LSM) - zircônia estabilizada com ítria (ZEI). Outro aspecto importante em PaCOS é o uso de material de eletrólito com uma condutividade iônica maior do que a da zircônia em temperaturas mais baixas. Essa característica é importante para a redução da temperatura de operação da PaCOS minimizando os problemas relacionados com a alta temperatura de operação, sendo Céria dopada com ítria (CY) um exemplo desse tipo de material. Por isso, para o uso de CY como eletrólito em PaCOS é importante avaliar a possibilidade de formação de fase isolante envolvendo esse material e o material do catodo, como perovskitas de lantânio. Para avaliar possíveis reações entre céria dopada com ítria e dois tipos de perovskitas usadas como catodo, LSM and LSCF, foi realizado, neste trabalho, a dopagem de CY com dois conjuntos de íons: La, Sr, Mn e La, Sr, Fe, Co. A dopagem provocou aumento da condutividade elétrica do grão enquanto que a condutividade efetiva do contorno de grão decresceu. Contudo a condutividade total não foi comprometida com a dopagem. A dopagem com La, Mn e Sr forneceu amostra de Céria dopada com Itria mais estáveis em alta temperatura e atmosfera redutora.

Propriedades reológicas e microestruturais de eletrólito de ZrO2/Y2O3

Para reduzir a temperatura de operação das pilhas a combustível de óxido sólido (PaCOS), estruturas com filmes finos de eletrólito depositados, por aerografia, sobre suportes de anodo porosos foram desenvolvidas. As barbotinas, empregadas para fabricação dos filmes, foram preparadas a partir de suspensões com pós de zircônia estabilizada com ítria (ZEI), solventes, dispersantes, ligantes e plastificantes apropriados. Neste trabalho, foi feito o estudo da influência dos ligantes sobre a estabilidade das suspensões e as propriedades microestruturais dos filmes de ZEI. Três barbotinas foram elaboradas com composições diferentes de ligantes (0,5; 1,0 e 2,0 % p/p). Todas apresentaram comportamento de fluidos pseudoplásticos e tixotrópicos, de acordo com medidas de viscosidade e taxa de cisalhamento. Os filmes foram sinterizados a 1500 ºC/6h. As micrografias eletrônicas de varredura (MEV) foram tratadas através do programa Quantikov para determinar a porosidade do filme e o tamanho médio de grão da ZEI. Os filmes apresentaram porosidade adequada para serem empregados como eletrólito das PaCOS (entre 0,2 e 0,4 % ) e tamanho médio de grão entre 2,0 e 6,0 µm. A técnica de aerografia é adequada para fabricar eletrólito de ZEI para PaCOS.