On the link between bulk and surface properties of mixed ion electron conducting materials Ln0.5Sr0.5Co0.8Fe0.2O3−δ (Ln = La, Pr, Nd)

Abstract

This work tests the hypothesis that the surface oxygen exchange rate and bulk oxygen anion diffusivity are intrinsically linked in mixed ion-electron conducting oxides. In contrast to other studies that measure these parameters in a linked experiment, this study combines data from in situ neutron powder diffraction (NPD), synchrotron X-ray diffraction (XRD), pulse isotopic oxygen exchange, X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) studies of Ln_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (Ln = La, Pr, Nd) solid oxide fuel cell (SOFC) cathode materials. The Pr and Nd containing materials were found to exhibit higher oxygen exchange rates and decreased electrode impedance when compared to the La-based material. It is proposed that the observed increase in performance is directly linked to high oxygen mobility in the Pr and Nd containing materials. The oxygen mobility is characterized in terms of the oxygen vacancy concentration and oxygen atomic displacement derived from the NPD data.