Development of mixed-conducting oxides for gas separation

Abstract Mixed-conducting oxides have been used in many applications, including fuel cells, gas-separation membranes, sensors, and electrocatalysis. We are developing a mixed-conducting, dense ceramic membrane for selectively transporting oxygen and hydrogen. Ceramic membranes made of Sr-Fe-Co oxide, which has high combined electronic and oxygen ionic conductions, can be used to selectively transport oxygen during the partial oxidation of methane to synthesis gas (syngas, CO+H 2 ). We have measured the steady-state oxygen permeability of SrFeCo 0.5 O x as a function of oxygen partial-pressure gradient and temperature. At 900°C, oxygen permeability was ≈2.5 scc·cm −2 ·min −1 for a 2.9 mm thick membrane and this value increases as membrane thickness decreases. We have fabricated tubular SrFeCo 0.5 O x membranes and operated them at 900°C for >1000 h during conversion of methane into syngas. The hydrogen ion (proton) transport properties of Ba(Ce,Y)O 3− δ were investigated by impedance spectroscopy and open-cell voltage measurements. High proton conductivity and a high protonic transference number make Ba(Ce,Y)O 3− δ a potential membrane for hydrogen separation.