ELECTRODE PROPERTIES OF SR-DOPED LAMNO3 ON YTTRIA-STABILIZED ZIRCONIA.1. 3-PHASE BOUNDARY AREA

The interface microstructure of the state-of-the-art cathode material for solid oxide fuel cells, SrxLa1-xMnO3 (SLM), was investigated with respect to its electrochemical performance. The interface microstructu re was characterized by grain size and coverage of SLM on the electrol yte surface. Variation of the grain size was obtained by using three d ifferent sintering temperatures, whereas variation of the coverage was obtained by using two powders with a different morphology. This resul ted in a set of six cathode/electrolyte samples with different combina tions of grain size and SLM coverage at the interface. The cathode ove rpotential, as a measure for the electrochemical performance, could no t be related to the length of the three-phase boundary. Based on the c onstriction resistance occurring in the electrolyte a model was develo ped which provides an estimate for the width of the active three-phase boundary zone. This zone is most likely to extend outside the cathode particle across the zirconia surface. The width calculated in this wa y was found to vary in the range of 0.03 to 0.07 mu m for the differen t electrode microstructures. It is argued that the actual values may b e smaller by one or two orders of magnitude.