On the link between bulk structure and surface activity of double perovskite based SOFC cathodes

The surface oxygen exchange rates for NdBaCo2O5 + d (NBCO), PrBaCo2O5 + d (PBCO), and GdBaCo2O5 + d (GBCO) were measured between 573 K and 973 K using an isotopic pulse exchange technique. Impedance spectroscopy was utilized to compare these surface rates with electrode performance. Both experiments showed NBCO to be the most active material, with both PBCO and GBCO approximately equal but with lower surface exchange rates and higher electrode area specific resistance. A discontinuity in both data sets was linked to a crystal phase transition in GBCO. It is proposed that the electrode performance is limited by the oxygen exchange rate.