Assembling Single Cells to Create a Stack: The Case of a 100 W Microtubular Anode-Supported Solid Oxide Fuel Cell Stack

Abstract

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).