Papers by Keyword: Solid Oxide Fuel Cell (SOFC)

Abstract: In comparison to other Periodic Table elements, rare earth elements demonstrate long-term stability and strong conductivity. Ceria nanomaterial has found many applications in numerous technologies. Doped ceria was prepared by many wet chemical methods. In this paper, we examine the electrical properties of the ceria after adding three dopants, two of which are rare earth elements (Gd and Nd) and one metal (Ca). The compositions, Ce_0.75Gd_0.05Nd_0.2O₂ and Ce_0.75Gd_0.05Nd_0.14Ca_0.06O₂, were formed using the WOWS (without water and surfactant) Sol-Gel method. The X-ray diffraction (XRD) technique was used to investigate the crystallinity of nanostructures. The structure of both samples was cubic. For the electrical measurements, the Precision Analyzer was used for doped Ceria as a function of temperature. With the variation in composition, the electrical properties changes.

Abstract: This paper presents the results of performance evaluation of anode-supported solid oxide fuel cells (SOFC) with magnetron sputtered YSZ/CGO bilayer electrolyte, and composite LSCF-CGO cathode. Deposition of the YSZ/CGO electrolyte with the thickness of up to 14 microns was performed on the commercial anode substrates with dimensions of 5×5 cm². The LSCF-CGO cathode of the fuel cells was formed by the screen-printing method. The microstructure of the YSZ/CGO bilayer electrolyte and LSCF-CGO cathode was studied by scanning electron microscopy. Comparison of the fuel cells performance with different thicknesses of the YSZ and CGO layers was carried out by measuring current-voltage and power characteristics, and also by testing the long-term stability of cell power at the temperature of 750 °C and voltage of 0.7 V.

Abstract: A thin ScSZ electrolyte with a large area was synthesized using the tape-casting method. The conductivity of 0.095 S cm^-1 at 800°C was achieved. The maximum power density of a single cell reached 368 mW cm^-1 at 800°C. To make a large electrolyte battery more suitable, our study improves the casting method of preparing a dense, porous electrolyte substrate that promotes surface roughness of the electrolyte. However, it is difficult to control the thickness of the substrate, meaning that further improvements are needed.

Abstract: Fabrication of Solid Oxide Fuel Cells (SOFCs) electrolytes by Electrophoretic Deposition (EPD) was the target of our study. For such purpose, thin layers of Yttria Stabilized Zirconia (YSZ) were electrophoritically deposited on pre-sintered NiO-YSZ pellets. A thin graphite film on each pellet was painted to make it conductive and can act as a working electrode for EPD. In this research acetylacetone-ethanol mixture (1:1 by vol.) was selected as the solvent and by applying different electrical fields (25, 50, 75, 100V/cm) in different deposition times (6, 3, 2, 1.5 min respectively), the obtained layers were examined. It was revealed that although electrical field multiplied deposition time remained constant in our experiments, the thicknesses of the deposited films were increased with increasing the applied electrical field which could not be explained easily by the Hamaker equation. For the next step, sintering of the deposited layers which prepared by applying 75 V/cm electrical field during 2 minutes was investigated. It was found that although the sintering processes were activated at 1250oC, 2 hours soaking time was not enough to produce a non-permeable layer. On the contrary, the layer which sintered at 1400oC for 2 hours was dense and crack-free. The thickness of the obtained layer was about 7μm and this layer seemed to be suitable for electrolyte of SOFCs.

Abstract: Degradation of cathode induced by sodium chloride in air has been investigated for (La_0.8Sr_0.2)_0.98MnO₃ (LSM). Cell performance was measured by volatilizing NaCl into the air supplied to the cathode at a constant current density of 200 mA cm^-2 up to 100 h. At 800 °C, an exposure to 30 ppm NaCl caused negligible degradation of LSM cathode at least for 100 h, yet degradation became obvious with increasing NaCl concentration. Slight change in the composition of the cathode materials was observed which may lead to the gradual degradation of cell performance. In addition, cell performance degradation was compared between 700 °C to 900 °C, being poisoned by 30 ppm NaCl. Degradation was negligible for the LSM cathode, while it showed slightly poor tolerance at 700 °C due to the decomposition of the cathode material. Further study should be done to clarify the long-term influence of NaCl on cathode performance.

Abstract: The objective of this work was to investigate high temperature oxidation behavior of AISI 430 stainless steel, which was proposed to use as interconnector in the planar solid oxide fuel cells (SOFCs). The oxidation of the alloy has been conducted at 700°C, 800°C and 900°C for 12h-96h by thermal gravimetric analysis (TGA) system. The oxide surface morphology, cross-section microstructure and the chemical composition of the oxide scales were performed by FEG-SEM and EDX. The X-ray diffraction (XRD) was used to identify the oxide phases formed on the alloy and to determine the residual stress in the scale. It has been found that the oxide scale composed of a inner Cr₂O₃ layer and an outer Mn_1.5Cr_1.5O₄ layer. The residual stresses in both oxide layers are compressive and the residual stress evolutions in the two layers are different according the oxidation temperature.

Abstract: Several methods for processing tubular anodes for solid oxide fuel cells have been developed, but many of them are expensive and sophisticated, therefore, there is a great interest in researching the use of a simple process to produce them. In this paper, the results of using slip casting for processing minitubes of NiO-8YSZ with the dimensions of 100x5x1 mm are presented. This is a versatile method for obtaining complex geometries with a suitable surface finish and dimensional precision at low cost compared with ceramic processing which uses high energy consumption and/or has high startup costs. In order to carry out this study, an aqueous slurry of an oxide mixture of NiO-8YSZ with poly-etilenglycol as a dispersant agent was used. The modification of the ratio of water:ceramic powders, the composition NiO:x8YSZ (30, 50 and 70 in wt.) and the casting time (3 to 30 min) were also applied. The minitubes obtained were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopy of dispersive energy (EDS). The results show that slip casting is an appropriate method to obtain NiO-8YSZ minitubes. Minitubes of varying composition (30, 50 and 70% in wt. of NiO) with dimensions of 100x5x1 mm were obtained showing an excellent porosity (higher than 96% in v/v) and a homogeneous distribution of NiO and 8YSZ particles. XRD analysis confirms the presence of starting oxides before and after the casting process.

Abstract: Solid electrolytes based on stabilized zirconia have been studied a long time ago in its cubic phase because of its electrical properties, which make them excellent candidates to be used in applications such as oxygen sensors and solid oxide fuel cells [1], [2]. Lambda sensor or oxygen sensor, as it is also known, is a device that measures the oxygen concentration of the gases that flow through the exhaust pipe. Physically, the lambda sensor has two electrodes. The outer which is exposed to the exhaust gases and the inner to the air (reference) [3]; these electrodes are made, generally, of porous platinum. The ceramic material, i.e., zirconium oxide, is placed in between the electrodes, so the oxygen ions can move from one electrode to another. As one of the electrodes is exposed to the reference gas, the voltage generated is a measure of the concentration of oxygen in the exhaust gases [4].

Abstract: This paper presents a control strategy of solid oxide fuel cell (SOFC) generation system integrated into microgrid. To enhance the dynamic response of SOFC, storage battery is paralleled via a DC bus, and the hysteretic control of bi-directional DC-DC converter is adopted. The common DC-AC inverter adopts an improved droop control. The active synchronization control is applied to ensure the smooth mode transition of microgrid. The simulation results show the dynamic performance of SOFC generation system in different operation modes.

Abstract: Through computer aided design, manufacturing and evaluation, various ceramics dendrites with spatially ordered micro cavities were successfully fabricated by utilizing stereolithography. Micrometer order ceramic lattices were propagated spatially in computer graphic space. Ceramics nanoparticles were dispersed in to photo sensitive liquid resins to obtain thixotropic slurries. The paste material was spread on a grass substrate by using a mechanical knife edge, and an ultra violet micro pattern was exposed to create cross sectional solid layer. After the layer stacking process, the obtained composite precursor was dewaxed and sintered in an air atmosphere. By the micro patterning stereolithography, solid electrolyte dendrites of yttria stabilized zirconia with spatially ordered porous structures were fabricated for fuel cell miniaturizations. Gaseous fluid profiles and pressure distributions in the formed ceramic lattices with various porosity percent were visualized and analyzed by a finite element method. Subsequently, alumina micro photonic crystals with a diamond lattice structure were fabricated. Electromagnetic wave properties were measured by using a terahertz time domain spectroscopy. A complete photonic band gap was exhibited, and a localized mode to select the wavelength was obtained by introducing a defect cavity.