Development of mixed-conducting oxides for gas separation

Mixed-conducting oxides have been used in many applications, including fuel cells, gas separation membranes, sensors, and electrocatalysis. The authors 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{sub 2}). The authors have measured the steady-state oxygen permeability of SrFeCo{sub 0.5}O{sub x} as a function of oxygen-partial-pressure gradient and temperature. At 900{degrees}C, oxygen permeability was {approx}2.5 scc{center_dot}cm{sup {minus}2}{center_dot}min{sup {minus}1} for a 2.9-mm-thick membrane and this value increases as membrane thickness decreases. The authors have fabricated tubular SrFeCo{sub 0.5}O{sub x} membranes and operated them at 900{degrees}C for >1000 h during conversion of methane into syngas. The hydrogen ion (proton) transport properties of yttria-doped BaCeO{sub 3} were investigated by impedance spectroscopy and open-cell voltage measurements. High proton conductivity and a high protonic transference number make yttria-doped BaCeO{sub 3} a potential membrane for hydrogen separation