Cermet membrane reactors for oxygen separation with low silver content

In this contribution we first present our results for oxygen separation/membrane reactors with silver and doped ceria and our approach to manufacturing cermets with low metal content (silver < 10 vol%) and then we concentrate on our more recent results on the Sc-stabilized zirconia and silver. Dense composites of silver and Sc-stabilized ZrO2 (Ag-ScSZ) are manufactured from ScSZ sub-micrometric particles coated with Ag via Tollens’ reaction. There is a significant reduction in level of silver, (11.9 vol %), required for percolation. This ensures a metallic conductivity of 186 S cm-1 and an oxygen flux of 0.014 umol cm-2 s-1 at 600°C for a 1-mm thick membrane when used as a pressure-driven separation membrane between air and argon. We measure and model the impedance of a non-percolating sample to show that oxygen transport in the silver droplets inside the composite is dominated by diffusion of neutral species and not by the charge transfer reaction at the interface between ScSZ and silver. The model establishes that oxygen transport takes place in both silver and ScSZ but it is still dominated by transport in the ionic conductor and that the surface of a separation membranes does not require further activation as the silver can reduce oxygen readily.