Theory and examples for the application of electron blocking microelectrodes to the study of ion transport and electrode processes in mixed electronic and ionic conductors were given for a couple of mixed conducting oxide perovskites. Emphasis was laid on the analysis of steady state current–voltage and cyclic voltammetric curves. Yttria-stabilized zirconia was used as the O ion conducting micro-contact material. The measurements were performed between 500 and 750C both on encapsulated and non-encapsulated oxide surfaces in order to detect the relative importance of surface O exchange as compared to bulk O ion transport and changes of stoichiometry. Gd0.8Sr0.2CoO3-δ and La0.8Sr0.2FeO3-δ proved to be typical mixed conductors with medium O ion conductivities. Both showed increasing ion conductivities for decreasing O activities indicating a typical vacancy transport mechanism of O ions. At 700C in air, a value of 2 x 10-4S/cm was obtained for the O ion conductivity of Gd0.8Sr0.2CoO3-δ; with a very weak dependence upon the O partial pressure. A value of 1.2 x 10-5S/cm was found for La0.8Sr0.2FeO3-δ. The O-ion conductivity of La0.8Sr0.2FeO3-δ was proportional to pO2-0.22 within the investigated range of temperatures and O partial pressures between 10 and 10-4bar. In addition to that, a series of manganites was investigated with the composition A0.7E0.3MnO3 (A = Gd, Y, Pr and E = Ca, Sr). The presence of slow diffusion coupled redox processes could be detected in all manganites at low and high O activities versus air. The O-ion conductivity was considerably lower than 10-5S/cm in all investigated manganites. Nevertheless, the comparison of results for glass encapsulated and non-encapsulated micro-contacts showed that Pr0.7Ca0.3MnO3 and in particular Pr0.7Sr0.3MnO3 were quite active catalysts for the O electrode reaction at the three-phase boundary air/zirconia/manganite, whereas Y0.7Sr0.3MnO3 does not catalyze the O electrode reaction significantly at the surface.

Studies of Ionic Transport and Oxygen Exchange on Oxide Materials for Electrochemical Gas Sensors. H.D.Wiemhöfer, H.G.Bremes, U.Nigge, W.Zipprich: Solid State Ionics, 2002, 150[1-2], 63-77