REACTION-KINETICS AND MICROSTRUCTURE OF THE SOLID OXIDE FUEL-CELLS AIR ELECTRODE LA0.6CA0.4MNO3/YSZ

In order to make clear the relationship between the microstructure of the porous oxide layer and electrochemical properties of air electrodes of solid oxide fuel cells, air/porous oxide/yttria stabilized zirconia, complex-impedance and cathodic polarization were measured on the air/La0.6Ca0.4MnO3/YSZ electrodes at 900-1000-degrees-C with the porous La0.6Ca0.4MnO3 layers of different morphology prepared by different method and different firing temperatures. From the SEM images of the cross section of the interface, the length of the air/La0.6Ca0.4MnO3/YSZ triple-phase boundary and the area of the closely contacted La0.6Ca0.4MnO3-particles/YSZ interface were estimated. It was shown that the reaction rate was essentially proportional to the length of the triple-phase boundary, while the electrode capacitance was largely proportional to the closely contacted area. Although the reaction rate depended on the electrode morphology, the kinetics of the rate-determining reaction for small overpotential was found to be essentially the same irrespective of the different morphology of the oxide layer. The electrode interface conductivity at 1000-degrees-C for a unit length of the triple-phase boundary was calculated to be (3.4 +/- 0.8) x 10(-4) S cm-1, and the electrode capacitance for a closely contacted area of the oxide/YSZ interface was about 5000-mu-F cm-2.