Synthesis and evaluation of nano-size lanthanum strontium manganite–yttria-stablized zirconia composite powders as cathodes for solid oxide fuel cells

Nano-sized (50 nm) lanthanum strontium manganite (La0.8Sr0.2MnO3, LSM) particles are deposited on yttria-stablized zirconia (8YSZ) by synthesizing LSM particles in situ in an YSZ-dispersed solution. As the LSM content is decreased from 80 to 25 wt.%, 50 wt.% powder shows the best microstructure and phase connectivity. This composite, when used as a cathode in a button cell, also has the highest power density of 791 mW cm−2 at 800 °C and the lowest values of the cathode polarization resistance and high-frequency arc (0.315 and 0.120 Ω cm2, respectively). Initially, the low-frequency arc shows a rapid decrease as the LSM content is reduced from 80 to 60 wt.%. After this, an abrupt drop at 50 wt.% LSM content is followed by a slow decrease in the low-frequency arc with further decrease in the LSM content. The results suggest that the high-frequency arc is related to charge transfer and the low-frequency arc to the site density of the triple-phase boundary (TPB). A new parameter, the charge-transfer efficiency of the TPB site, is defined and used to explain further the observed effect of LSM content on YSZ.