Integrated Fabrication Processes for Solid-Oxide Fuel Cells Using Thermal Plasma Spray Technology
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imposing a dc jet on the rf plasma, the particle velocity can be significantly increased—up to 60 m/s at atmospheric pressure. Using this technology, dense YSZ films with a gas permeability lower than 5.7 107 cm4 g1 s1 have been produced.1 A study of the hybrid plasma deposition of the anode, using NiO as a source material, reveals that the Ni particles in the sprayed samples are not as spherical as in sintered samples and have a larger specific surface area. Consequently, the Ni grains are in better direct contact to each other. The lamellar structure of the sprayed film allows a significant reduction in the nickel content in the anode without compromising its electrical properties. This is desirable because the high thermalexpansion coefficient of Ni compared with that of YSZ can lead to the generation of important internal stresses in the final cell. In an earlier study using a standard Ar-O2 plasma-induction system, electrolytes were produced at 48 kW rf input
François Gitzhofer, Maher Boulos, Joachim Heberlein, Rudolf Henne, Takamasa Ishigaki, and Toyonobu Yoshida Introduction In the manufacture of solid-oxide fuel cells (SOFCs), thermal-plasma technology, especially plasma spraying, offers several advantages, the most important of which is the ability to achieve considerably higher deposition rates than those that can be obtained with such approaches as physical or chemical vapor deposition (PVD or CVD). This article describes an international collaborative research project partially funded by NEDO (New Energy and Industrial Technology Development Organization, Japan) and carried out at five research laboratories around the world: at the University of Tokyo and National Institute for Research in Inorganic Materials (NIRIM) in Japan, the University of Minnesota in the United States, the University of Sherbrooke in Canada, and DLR—Stuttgart in Germany. The objective of the project was to conduct a comparative study on the possible use of four thermal-plasma spraying techniques for the integrated fabrication of SOFCs. Presently, the production of SOFC components and cells is mainly carried out by a series of sintering processes that are timeconsuming and costly, requiring several heating and cool-down phases. Plasma spraying based on dc- or rf-induction plasma technologies has great potential
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for bringing down production costs. These technologies also allow for the modification of the SOFC design to considerably reduce the thickness of the electrolyte oxygen-ion conducting layer, which in turn reduces the internal electrical resistance of the cell. The techniques considered in the present study were dc/rf-hybrid plasma spraying (HYPS); rf-induction plasma spraying (IPS), with and without a supersonic nozzle; triple-torch plasma spraying (TTPS); and high-velocity, low-pressure, dc plasma spraying (HVLPPS). Each of these techniques was used to prepare the required high-density, gas-tight, solid-electrolyte yttria-stabilized zirconia (YSZ) layer; the porosity-controlled Ni/YSZ cermet thick layer (as the
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