PrBaCo2O6−δ-Ce0.8Sm0.2O1.9 Composite Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells: Stability and Cation Interdiffusion

The single-phase oxide PrBaCo2O6−δ and composites (100 − y)PrBaCo2O6−δ-yCe0.8Sm0.2O1.9 (y = 10–30 wt.%) were investigated as cathode materials for intermediate-temperature solid oxide fuel cells. The chemical compatibility, cation interdiffusion, thermal expansion and dc conductivity were studied. As a result, strong interdiffusion of Pr and Sm was found between PrBaCo2O6−δ and Ce0.8Sm0.2O1.9. This leads to only insignificantly decreasing thermal expansion coefficient of composite with increasing fraction of Ce0.8Sm0.2O1.9 and, thus, mixing PrBaCo2O6−δ with Ce0.8Sm0.2O1.9 does not improve thermal expansion behavior of the cathode material. Moreover, formation of poorly-conducting BaCeO3, caused by chemical interaction between the double perovskite and doped ceria, was shown to lead to pronounced drop in the electrical conductivity of the composite cathode material with increasing Ce0.8Sm0.2O1.9 content.

Interdiffusion in Ionic Compounds

In this chapter, we review the Nernst-Planck equation describing the cation interdiffusion coefficient, the two tracer cation diffusion coefficients and the thermodynamic factor in ionic compounds and how it is related to the analogous Darken-Manning relationship in binary alloy systems. We make use of the Onsager flux equations of non-equilibrium thermodynamics to rigorously address the problem. The recently found correction factor to the Nernst-Planck equation is analyzed visually by means of computer simulation