Composite Transition Of Metal Oxide CeO₂ Electrolyte Preparation And Performance Study

In the present work, the composite electrolytes materials Ce0.8Gd0.2O1.9-x mol% Co₃O₄?x=0, 0.5,1,2,3? and Ce0.8Gd0.2O1.9-x mol% TiO₂?x=0, 0.5, 1, 2, 3? were synthesized by means of co-precipitation method. Co₃O₄ and TiO₂ are added into the electrolyte ceramic, Ce0.8Gd0.2O1.9?GDC?, during powder preparation to investigate the effects of the presence of Co₃O₄ and TiO₂ on the densification, microstructure and electrical properties of GDC electrolyte. Electrolyte-supported solid oxide fuel cells?SOFC? fabricated with Ce0.8Gd0.2O1.9-x mol% Co₃O₄?x=0, 0.5, 1, 2, 3? and Ce0.8Gd0.2O1.9-x mol% TiO₂?x=0, 0.5, 1, 2, 3?electrolytes were studied and compared with the fuel cell with GDC as electrolyte.For the Ce0.8Gd0.2O1.9-x mol% Co₃O₄?x=0, 0.5, 1, 2, 3? mixtures, the XRD analysis indicates that there were no byproducts; All the electrolytes are found to be ceria-based solid solutions of fluorite type structure. The grain size is increased by a small addition of Co₃O₄ when the sintering temperature is 1400°C. Co3+ has a tendency to enhance grain boundary mobility, probably due to the large distortion of the lattice at the grain boundary that promotes the mass diffusivity and consequently the sinterability, and then increase the grain size. The grain boundary conductivity of GDC-Co₃O₄ composites decrease with increasing Co₃O₄ content. Segregation occurs over a small grain-boundary area as the grain size increases, the Co3 O 4 and impurities can form a continuous and uniform glassy phase layer along the grain boundary. Therefore, the transports of oxygen ions are prevented. The V-I characteristics of single cell show that the maximum output power density was 22mW/cm2 at 800 oC for the cell with GDC-3mol% Co₃O₄ as electrolyte.For the Ce0.8Gd0.2O1.9-x mol TiO₂?x=0, 0.5, 1, 2, 3? mixtures, the XRD analysis of the samples reveals in the interval from 0 up to 1 the existence of a cubic fluorite phase like that of pure CeO₂. Above x=2 a second phase identified by a small XRD peak as Gd2Ti2O7. The grain growth is promoted by adding a small amount of TiO₂. Precipitates inhibit the grain growth and lead to the decreases in grain size with the TiO₂ addition over 2 mol%, due to the pinning effect. This modification in chemical composition also results in a decrease in activation energy and thus a tendency to markedly enhance grain boundary mobility. The maximum power density?MPD? of the composite electrolyte single cell at 800°C, 90 mW/cm2, is higher than that of a GDC single cell at 800°C.