Stabilized bismuth oxide–noble metal mixed conducting composites as high temperature oxygen separation membranes

Oxygen concentration cells, with dense dual phase composite membranes made from erbia-stabilized bismuth oxide and a noble metal (Au, Ag), were investigated in the temperature range 650–850°C under controlled oxygen partial pressure gradients. An electrochemical treatment was applied to interpretation of the oxygen permeation data. It is found that the composite membranes exhibit high oxygen permeability relative to the single phase bismuth oxide, since oxygen ions and electrons are allowed to transport through the oxide and metal phase, respectively. The oxygen permeability of the silver-containing composite is at least one order higher than that of the gold-containing one, which can be explained by the fact that silver has a higher catalytic activity than gold for the surface oxygen exchange reaction and thus less limitations are exerted on the overall oxygen transport.