IN PRESENTLY USED MCFC LITHIATED MIO CATHODE ARE DISSOLVED BY THE MOLTEN CARBONATE ELECTROLYTE AND DEPOSITED IN THE ELECTROLYTE CAUSING A SHORT CIRCUIT. IN ORDER TO AVOID THIS CORROSION PROBLEM THE PROPOSED PROJECT AIMS AT REPLACING H2O BY OTHER MATERIALS (E.G. DOPED LIFEO2). KEY ISSUES ARE GOOD ELECTRICAL CONDUCTIVITY COMPATIBILITY WITH THE ELECTROLYTE, GOOD MORPHOLOGICAL CHARACTERISTICS SUITABLE FOR MASS PRODUCTION.
Several techniques for characterising ceramic oxide MCFC cathode materials have been investigated and developed. It became clear that the cyclic voltammetry method cannot be applied at the present time as a standard technique for determining the dissolution of materials into the carbonate melt. Simple pot tests turned out to be satisfactory for measuring the short term stability of compounds.
Extensive investigations were carried out on lithium ferrite. A good understanding of the influence of cation stoichiometry and doping with M2+ elements on the electrical conductivity was obtained and of the influence of gas atmospheres during calcining, sintering and operation. The specific electrical conductivity of this material can be increased to the required level by doping. The dissolution and precipitation behaviour of the dopants turned out to be the crucial factors in using lithium ferrite and require further study.
THE PROGRAMME FOCUSSES IN FIRST INSTANCE ON DOPED LI-FEO2, A CHEAP MATERIAL WHICH PROVED TO HAVE MODERATE SOLUBILITY IN PRELIMINARY CORROSION TESTS UNDER SIMULATED CATHODE CONDITIONS. THE RESISTIVITY OF THE OXIDE WILL BE REDUCED BY THE INCORPORATION OF SUITABLE METAL DOPANTS IN THE PRISTINE MATERIAL. THE TARGET VALUE SET FOR RESISTIVITY IS < 10 OHM.CM AT 650 CELSIUS DEGREES FOR A 50 % POROUS BODY.
AS THE FINAL PROPERTIES OF THE DOPED OXIDE ARE CLOSELY RELATED TO THE SYNTHESIS PROCEDURE, THE DOPING STUDIES WILL BE CARRIED OUT IN PARALLEL WITH THE DEVELOPMENT OF AN ADVANCED POWDER PREPARATION TECHNIQUE, BASED ON THE SO-CALLED SOL-GEL PROCESS.
THE RESERACH PROJECT WILL BE CARRIED OUT IN TWO DIFFERENT STAGES, IE (1) DEVELOPMENT OF SYNTHESIS TECHNIQUES AND (2) MATERIALS DEVELOPMENT.
1) DEVELOPMENT OF SYNTHESIS TECHNIQUES:
ADAPTATION AND OPTIMIZATION OF THE SOL-GEL TECHNIQUE FOR THE SPECIFIC REQUIREMENTS OF THE MATERIAL UNDER INVESTIGATION FOR THE PRODUCTION OF ISODISPERSE SPHERICAL LIFEO2 PARTICLES.
THE PARTICLE SIZE (WHICH SHOULD BE IN THE RANGE BETWEEN 1 AND 10 MICRONS) CAN BE ADJUSTED BY CHOOSING THE RIGHT SURFACTANTS.
IN THE NEXT STAGE OF THE PROCESS, THE EMULSION DROPLETS ARE CONVERTED INTO SOLID GELS AFTER REMOVAL, THE SOLIDIFIED PARTICLES ARE DRIED, CONVERTED INTO OXIDES AND DENSIFIED AT ELEVATED TEMPERATURES.