Yanhai Du

Extruded Tubular Strontium- and Magnesium-Doped Lanthanum Gallate, Gadolinium-Doped Ceria, and Yttria-Stabilized Zirconia Electrolytes Mechanical and Thermal Properties

Thermal properties and mechanical strength of ceramic fuel-cell components are critical in allowing for rapid start-up and operational stability at high temperatures of solid oxide fuel cell (SOFC) systems. Tubular SOFC electrolytes were prepared using a plastic extrusion technique from a dough containing the electrolyte powders and additives. Strontium- and magnesium-doped lanthanum gallate (LSGM), gadolinium-doped ceria (CGO), and 8 mol % yttria-stabilized zirconia (YSZ) were studied. Burst failure strength, thermal expansion coefficient, and thermal shock resistance of the extruded tubular LSGM, CGO, and YSZ electrolytes were investigated and compared. Three-point bending strength of these three extruded electrolyte materials were tested at room temperature, 600, 800, and 1000°C in air, and the results are discussed.

Optimisation parameters for the extrusion of thin YSZ tubes for SOFC electrolytes

Abstract Thin wall thickness (0.25–0.35 mm) tubes, as tubular electrolytes of solid oxide fuel cells, were successfully fabricated from yttria stabilised zirconia (YSZ) by way of extrusion. Water-based additives and organic additives were studied. An economic and practical process was developed to achieve smooth, linear, and dense ceramic tubes with 2.7–2.8 mm diameter. The microstructures of the selected tubes were examined. This paper describes the fabrication procedure, formulations and optimisation parameters for successfully extruding thin YSZ tubes.

Thermal Stability of Portable Microtubular SOFCs and Stacks

Rapid start-up times are a big challenge for high-temperature fuel cells such as solid oxide fuel cells (SOFCs), especially large-sized stacks with high power outputs. This paper presents the development of tubular and microtubular anode-supported SOFCs and the design and testing of the thermal stability of such single cells and stacks. It was demonstrated that single cells with various sizes have very good thermal shock resistance. Preliminary results also showed that stacks can be started up within minutes and withstand more than 50 thermal cycles and that single cells can withstand temperature changes of 550 °C/min. Several factors that affect the thermal stability are discussed.

Intermediate-Temperature SOFC Electrolytes

The electrolyte for solid oxide fuel cells (SOFC’s) must be stable in both reducing and oxidizing environments and have sufficient ionic, as well as low electronic, conductivity at the operation temperature. Present SOFC’s have extensively used stabilized zirconia, especially yttria stabilized zirconia, as the electrolyte. However, oxide ion conductors, such as doped ceria and perovskite-type oxides, have also been proposed as the electrolyte materials for SOFC’s, especially for reduced-temperature of operation (600°C to 800°C), now known as intermediate-temperature solid oxide fuel cells (IT-SOFC).

A Review of the Implications of Silica in Solid Oxide Fuel Cells

Silica is a well-known impurity in solid oxide fuel cell raw materials, namely NiO and yttria-stabilized zirconia (YSZ). At elevated temperatures silica will migrate to the grain boundaries, form insulating siliceous phases, and lead to a decrease in the ionic conductivity of the electrolyte. Furthermore, silica impurities have been shown to damage the anode/electrolyte interface, such that an overall decrease in cell performance and long-term stability is observed. Despite the fact that silica is ubiquitous in commercial-grade raw materials and can be incorporated from several extrinsic sources, it has negative effects on the solid oxide fuel cell, such that any further contamination should be avoided to prevent performance degradation and eventual cell failure. This paper reviews and outlines the sources and effects of silica on the solid oxide fuel cell, and attempts to determine a guideline for acceptable levels of silica contamination.

Portable Propane Micro-Tubular SOFC System Development

NanoDynamics Energy Inc. is developing a family of compact, integrated micro-tubular SOFC systems with high volumetric power density and multiple fuel options including methane, propane, diesel and JP8. The development program aims to bring to the market highly efficient, clean, and cost competitive fuel cell systems with outputs above 50We for portable power generation applications. Balance-of-plant (BoP), electronic controls, and power management systems have been identified and integrated with a partial oxidation reformer and SOFC stack. A system test for the integrated process chain was performed with our proprietary cell and system technologies. The performance of a system developed using a micro-tubular SOFC stack is evaluated for different operating conditions. Results from these studies will be presented. System design, integration, and control methodologies are also discussed. Introduction The increase in demand for energy and concern for environmental impacts has created an increase in demand for low-emission energy sources. Fuel cell systems can provide clean energy and with higher efficiency than typical generators (1). To meet increasing power and longevity demands of remote applications, lightweight, man portable fuel cell systems are under development. Balance of Plant (BoP), electronic controls, and power management sub-systems have been designed and tested for use with a micro-tubular solid oxide fuel cell (SOFC) stack and integrated partial oxidation (POX) reformer. This process addressed stack and reformer requirements as well as system level requirements for run-time, fuel type, and typical output loads. Each sub-system was tested under actual conditions to prove functionality, and lastly integrated with the POX reformer and SOFC stack for final evaluation. Proprietary technology allows for subsystem designs that are modular and scalable to meet larger portable power requirements. Sub-System Development Partial Oxidation (POX) Reformer Experiments were conducted to identify and optimize the operating conditions for hydrogen generation via POX reforming of propane fuel using a 2-stage reforming process carried out on proprietary catalyst formulations. ECS Transactions, 7 (1) 483-492 (2007) 10.1149/1.2729127,

Geometric Effects on Tubular Solid Oxide Fuel Cells

Micro-tubular solid oxide fuel cell systems have many desirable characteristics compared with their planar counterparts; however, there are many obstacles and difficulties that must be met to achieve a successful and economically viable manufacturing process and stack design. One of the most important parameters is the cell size and geometries. Anode-supported tubes provide an excellent platform for individual cells. A thin electrolyte layer applied to the outside of the tube helps to minimize polarization losses thus avoiding the difficulty of coating the inside of electrolyte or cathode-supported tubes. The stack design with anode supported tubes also avoids using a fuel chamber on the outside of the tube. Various geometries of the cell support, in terms of diameter, length, cross-section shape and arrangement were investigated. Results of geometric effects on micro-tubular SOFCs will be discussed and presented in this paper.

Thermal Stability of Portable Micro-Tubular Solid Oxide Fuel Cell and Stack

Rapid start-up times are a big challenge for high temperature fuel cells such as solid oxide fuel cells (SOFCs), especially large-sized stacks with high power outputs. This paper presents the development of tubular and micro-tubular anode-supported SOFCs and the design and testing of the thermal stability of such single cells and stacks. It was demonstrated that single cells with various sizes have very good thermal shock resistance. Preliminary results also showed that stacks can be started up within minutes and withstand more than 50 thermal cycles and temperature changes of 550C/min. Several factors that affect the thermal stability are discussed.

Assembling single cells to create a stack: The case of a 100 W microtubular anode-supported solid oxide fuel cell stack

Microtubular solid oxide fuel cell systems have many desirable characteristics compared with their planar counterparts; however, there are many obstacles and difficulties that must be met to achieve a successful and economically viable manufacturing process and stack design. Anode-supported tubes provide an excellent platform for individual cells. They allow for a thin electrolyte layer, which helps to minimize polarization losses, to be applied to the outside of the tube, thus avoiding the difficulty of coating the inside of an electrolyte or cathode-supported tubes, or the stack design problem of having a fuel chamber if the anode is on the outside of the tube. This article describes the fabrication of a traditional (Ni-YSZ) anode tube via extrusion of a plastic mass through a die of the required dimensions. The anode tubes were dried before firing, and tests were performed on the tubes to determine the effects of prefiring temperature on porosity. The porous tubes had a vacuum applied to the inside while being submerged in aqueous electrolyte slurry. Various parameters were examined, including vacuum pressure, submergence time, and drying conditions, and were studied using microscopy. Cathode coatings (based on both doped lanthanum manganite and doped lanthanum cobaltite) were applied using a brush-painting technique, and were optimized as a function of paint consistency, drying conditions, and firing temperatures. The finished tubes were then stacked in an array to provide the specific current/voltage requirements, using a brazing technique. This article will describe the output characteristics of a single cell and a small stack (of 100 W designed power output).

Using Flixweed Seed as a Pore-former to Prepare Porous Ceramics

Flixweed (Descurainia Sophia L.) seeds, known as an herbal medicine, for the first time are used as a promising pore-forming agent (pore-former) in ceramic technology. Flixweed seeds were selected because of their unique constant shape (oblong, 1.2 mm long with the aspect ratio of about 2) and narrow size distribution as well as their low-cost. Porous zirconia ceramics have been fabricated using flixweed seeds by tape casting technique. The dried tape-cast cut into disk-shaped pieces and were fired at 1400°C for 2h, resulting in porous zirconia disks with a bulk density of 3.96 g/cm3, total porosity of 34.6 ± 0.9% (open porosity 25.5 ± 0.7%, closed porosity 9.1 ± 0.3%) and a linear shrinkage of 21.5 ± 0.3%. The pore shape and size were similar in shape and size to the original pore-former.