Oxygen transport and chemical compatibility with electrode materials in scheelite-type LaWxNb1-xO4+x/2 ceramic electrolyte

LaWxNb1-xO4+x/2 ceramics (x = 0.16) were prepared via a solid state route and studied with respect to phase stability and mixed ionic and electronic conductivity under conditions of technological relevance for fuel cell applications. The chemical compatibility against standard cathode materials revealed that Sr-doped LaMnO3 could be used without detectable chemical interaction up to at least 1000 °C. Impedance spectroscopy measurements performed in the range 400-850 °C, using different atmospheres (air and N2+H2, both dry and water vapour saturated), suggest oxygen transport numbers equal to 1 under oxidizing conditions, and decreasing when exposed to extreme reducing conditions. The total conductivity at 800 °C increases from 1.4·10-3 S cm-1 in air to 2.5·10-3 S cm-1 in wet hydrogen and 6.1·10-3 S cm-1 in dry hydrogen, but the observed onset of n-type conductivity has little practical impact under typical fuel cell operating conditions.