Carry out basic research on materials for components of solid oxide fuel cells (cathode, anode, electrolyte), in order to improve electrical conductivity and reduce the electrode polarization.
For electrolytes, the Bi2O3-MoO3 system was investigated. The elaboration procedure was optimized and very interesting results were obtained in terms of conductivity at relatively low temperature (650-800 C). However, the stability of these materials under very reducing conditions is still questionable.
The mechanical properties of yttria stabilized zirconia have been enhanced with additions of alumina. These additions were only slightly detrimental in terms of electrical conductivity and the use of Al2O3-doped YSZ is strongly recommended. Furthermore, other dopants (Mg and Ca) were studied with interesting results. Partially stabilized zirconias and tetragonal zirconias were also studied and the results give a wide choice for the electrolyte.
Hydrogen oxidation has been studied in details on nickel anodes and on various cermets. It has been shown that a passivation of nickel could occur at high fuel consumption. In the case of YSZ-Ni cermets, it has been demonstrated that ceria doping of YSZ could reduce the risk of Ni passivation. The study of cermet deposition procedures showed that starting with Ni powders is better than with NiO powders. The effects of titania and ceria additions to YSZ on the electrical properties of YSZ in reducing atmosphere has been studied and showed that an important electronic conductivity can be induced with titania additions.
The reduction of oxygen on various manganites and cobaltites prepared by different ways has been studied. The detrimental effect of the reaction products wit YSZ has been clearly put in evidence and explained by a study of La2Zr2O7 and SrZrO3. La2Zr2O7 has a more detrimental effect and this could be avoided either by using high Sr contents or lanthanum deficient manganites. Electrochemical studies showed that at low overpotential manganites behave as metallic electrodes, while the electrochemical properties are enhanced at higher overvoltages. Very low firing temperatures (and thus small amount of reaction products) were achieved when composite cathodes YSZ-lanthanum deficient maganites were prepared by screen printing.
SOFC have the promise to produce electricity from coal or methane with 50-60% efficiency and a 10-100 times lower pollution as compared to conventional electricity generating systems. It is believed that with the present state of the art of ceramics technology, SOFC can be produced cost effectively. (Projects JOUE-CT90-0048 and JOUE-CT90-0027 actually develop 1 kW units with existing ceramic materials). New materials however with better ion (electrolyte) or electronic conductivities (electrodes) and lower polarization, may, in the long term, lead to SOFC with a still better performance and lower cost. In this project (JOUE-CT90-0044) basic R&D is therefore carried out on the following topics.
For cathodes, the La1-xSrxMnO3 system (LSM) is investigated, extending studies to large x values (x o 0.5). On the other hand, the influence of a partial substitution of La by smaller rare earth cations are determined, mainly for electrical conductivity at cathode polarization (INPG and University of Aveiro).
For anodes, cermets including Ni and titania or ceria doped zirconia or titania based oxides are tested (INPG and University of Aveiro).
Material research for electrolytes is focused on Bi2O3 and CeO2 based materials. The improvement of the mechanical and electrical properties of presently used ZrO2-8%Y2O3(YSZ) by proper dopant and/or the introduction of second dispersed phase (Al2O3) is tested (University of Pavia, CNR Messina, ICV).
Finally, different electrode/electrolyte interfaces with large area and defined morphology (porosity, grain size, thickness) are investigated with regard to stability and compatibility (INPG).
In the extension the above activities will be continued and intensified.
Funding SchemeCSC - Cost-sharing contracts