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Solid oxide fuel cells are currently constructed using a yttria stabilised zirconia electrolyte membrane. However, zirconia has a number of disadvantages associated with its use, such as the high operational temperatures required for it to exhibit acceptable levels of ionic conductivity. Alternative ceramics such as doped cerium oxide show promise as electrolytes capable of operating at reduced temperatures, but introduce additional problems such as electronic conduction and inferior mechanical properties. This paper describes the manufacture and characterisation of a number of prototype electrolytes consisting of a mixture of yttria stabilised zirconia and gadolinium doped ceria. Traditional ceramic processing techniques were used to produce the samples, which were then examined using dilatometry, impedance spectroscopy and X-ray diffraction. Results show a lowering of the ionic conductivity of zirconia with the addition of doped ceria. X-ray diffraction patterns obtained from the samples suggested that this effect could be attributed to the formation of a solid solution of ceria in zirconia. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell (SOFC) electrolytes are currently manufactured from yttria stabilised zirconia. A limitation of this material is the high operating temperatures needed for efficient operation, approximately 1000°C, as this can lead to sealing problems and require expensive nickel/chromium alloy auxiliary components. Alternative electrolytes, which allow operation at reduced temperatures, such as gadolinium doped cerium oxide have been suggested. However these ceramic materials often exhibit inferior mechanical properties. In this paper the manufacture and characterisation of composite electrolytes consisting of 3% yttria stabilised zirconia particles in a 20% gadolinia doped ceria matrix is described. Results suggest improvements in strength can be achieved by the composite approach. [ABSTRACT FROM AUTHOR]

The most important component of the solid oxide fuel cell (SOFC) is the dense electrolyte. Besides gastightness it must fulfill the requirements of good ionic conductivity and stability in reducing and oxidizing atmospheres. For this application yttria-stabilized zirconia is widely used. In this paper the effect of calcination temperature and milling time for zirconia powder stabilized with 8 mol% yttria (8YSZ) on the gastightness of the electrolyte layer was investigated. The influence of the addition of 0.77, 2 and 4 wt% Al2O3 to 8YSZ powder on the tightness and the sinterability of the electrolyte layer was studied. The performance of the cell with the electrolyte doped with 0.77 wt% Al2O3 was also investigated. The experiments show that the electrolyte layer, which was fabricated from 8YSZ powder (calcined at 1200°C) with particle size distributions of 0.25 μm–<0.3 μm ( d50), gives the lowest leak rate. The Al2O3 added to 8YSZ improved the electrolyte tightness by increasing the sinterability of the electrolyte layer and reducing the sintering time. The performance of a cell with Al2O3 added to the electrolyte is better than that of a cell with an electrolyte of pure 8YSZ, especially at operating temperatures between 800 and 900°C. [ABSTRACT FROM AUTHOR]

Realization of a solid oxide fuel cell (SOFC) operating at 700°C on a hydrocarbon fuel or gaseous H2 is an outstanding technical target. For the past 25 years, efforts to achieve this goal have been based on yttria-stabilized zirconia as the electrolyte, a NiO + electrolyte composite as the anode, a porous La0.85Sr0.15MnO3 (LSM) metallic perovskite as the cathode, and a La1− xSr xCrO3 ceramic as the interconnect material. This paper reviews progress in our laboratory on an alternate approach that would use a Sr- and Mg- doped LaGaO3 perovskite as the electrolyte, a Sm-doped ceria (SDC) as the anode or as a buffer layer with a NiO + SDC composite as the anode, a mixed oxide-ion/electronic conductor (MIEC) as the cathode, and a stainless steel as the metallic interconnect. [ABSTRACT FROM AUTHOR]

Electric field-assisted (flash) pressureless sintering experiments were carried out in ZrO ceramics doped with 10 mol% ScO and 1 mol% CeO (10Sc1CeSZ). All experiments were conducted isothermally at 1050 °C for 2-5 min with the application of a 100-150 V cm AC electric field at 1 kHz with 1-4 A limiting current in green compacts and in samples pre-sintered at different temperatures. Shrinkage level, structural phases and grain morphology data were collected by dilatometry, X-ray diffraction and scanning electron microscopy analyses, respectively. The results showed that for the same delivered electric power, the final shrinkage was higher for higher temperature applications of the electric field and for higher electric current pulses. Moreover, the higher the porosity, the higher the final densification of the flash-sintered 10Sc1CeSZ samples, showing that pores play a role as a preferential path in the flash sintering mechanism. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cell electrolytes are currently manufactured from zirconia. This is due to its high ionic conductivity and mechanical strength. However, a disadvantage of zirconia is the high temperatures required for efficient operation, greater than 900°C for cells not utilising thin supported electrolytes. A study to characterise the properties of an alternative composite solid electrolyte, based on a gadolinia doped ceria matrix surrounding yttria stabilised tetragonal zirconia particles is presented. Composite samples produced using 1, 2, 5, 10 and 20 wt% zirconia particles were characterised using a range of different experimental techniques including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, mechanical testing and impedance spectroscopy. Results showed a lowering in flexure strength of the experimental composite samples with the addition of particles. It is considered that the particles acted as regions where cracks could initiate. [ABSTRACT FROM AUTHOR]

The strength of symmetric anode/electrolyte/anode and cathode/electrolyte/cathode planar multiple electrode assemblies (MEAs), fabricated by screen printing electrodes onto pre-fired tape-cast electrolyte plates was measured in biaxial flexure. The electrolyte was Zr0.84Y0.16O1.92 (YSZ), the anode NiO/YSZ and the cathode La0.75Sr0.2MnO3−δ. The residual stress in the electrodes was estimated by curvature measurement after removal of one electrode. The residual stress in the anodes was very low (11 MPa) due to stress relief by extensive channel cracking. The residual stress in the cathodes was much higher (39 MPa) and was in reasonable agreement with the expected thermoelastic stress. The applied load at failure, and the stress in the electrolyte at failure (343 MPa), for anode MEAs were almost equal to those of electrolyte plates (374 MPa). This is consistent with the low residual stress and observed crack deflection by delamination at the anode/electrolyte interface. The applied load at failure, and the stress in the electrolyte at failure (182 MPa), for cathode MEAs were much lower. This is partially explained by the residual stress in the cathode acting to increase the applied stress intensity at defects in the electrolyte, but this effect is not large enough to explain fully the reduced strength. [ABSTRACT FROM AUTHOR]