Application of Nickel-Titania Cermets to Zirconia Solid Oxide Fuel Cells

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In the first place, preparation technology for nickel/titania cermets suitable for anode in solid oxide fuel cells (SOFC), especially porosity control, has been established, and thermal expansivity, mechanical strength, electrical conductivity and gas permeability has been measured. Cermets were obtained by the displacement reaction between NiO and Ti powders, 2NiO + Ti = 2Ni + TiO_2. Microstructure of the cermets became finer with decreasing the annealing temperature. Porosity decreased with increasing the applied pressure in dieforming and the annealing temperature. Mechanical strength was related only to porosity. The strength became higher with increasing the porosity and was 100 MPa at 30 %. The electrical conductivity at a porosity of 36.8 % was 1000 Scm^<-1>. The gas permeability was sufficiently high for SOFC and was in the range 10^<-2> to 10^<-3> cm^4g^<-1>s^<-1> at a porosity of 30 to 40 %.Electrode performance of cermets obtained by the established method has been tested using the samples on which films of ZrO_2 - 8 mol % Y_2O_3 (YSZ) were plasma-sprayd. Electrode conductivity increased with increasing the temperature and the PH_2O/PH_2 ratio, and reached 150 Scm^<-2> at 1000ﾟC in a H_2 - H_2O (30ﾟC) mixture. Cermets did not react with YSZ films at 1000ﾟC.Therefore, this cermet was applicable to SOFC.