Ni0.75Co0.25/(Gd2O3-CeO2) Anodes for Solid Oxide Fuel Cells

Electrochemical performance of solid oxide fuel cells based on Ni0.75Co0.25-GDC (Gd0.1Ce0.9O1.95) and Ni-GDC anodes were investigated and compared in order to understand the effects of (i) alloying Ni with Co and (ii) anode microstructure on the cell performance under hydrogen fuel. At the sintering temperature of 1300 degrees C for 5 h, the Ni0.75Co0.25-GDC anode showed a superior distribution and connection of grains to the Ni-GDC anode which had grain clustering structure in general. Grain growth and connection were found in both anodes when the sintering temperature was increased to 1350 degrees C for 3 h. This resulted in significant improvement of the anodic polarization resistance for the Ni-GDC anode but only minor change for the Ni0.75Co0.25-GDC anode. This research, however, showed that the Ni-GDC anode had higher anodic polarization resistance than the Ni0.75Co0.25-GDC anode, resulting in the better cell power density at all sintering conditions. The maximum power density obtained at 800 degrees C for the cell with the Ni0.75Co0.25-GDC anode was 118 mW.cm(-2). Impedance spectroscopy analysis showed that the total cell resistance of both cell types became progressively larger when the operation time was prolonged to 10 h at 800 degrees C, while the microstructure change was not observable by the SEM. The reason for the fast degradation will thus require further investigation.