Conductivity and oxygen permeability of a novel oxide Pr2Ni0.8 − x Cu0.2FexO4 and its application to partial oxidation of CH4

Iron-doped Pr2Ni0.8Cu0.2O4 was studied as a new mixed electronic and oxide-ionic conductor for use as an oxygen-permeating membrane. An X-ray diffraction analysis suggested that a single phase K2NiF4-type structure was obtained in the composition range from x = 0 to 0.05 in Pr2Ni0.8 − xCu0.2FexO4. It is considered that the doped Fe is partially substituted at the Ni position in Pr2NiO4. The prepared Pr2NiO4-based oxide exhibited a dominant hole conduction in the PO2 range from 1 to 10− 21 atm. The electrical conductivity of Pr2Ni0.8−xCu0.2FexO4 is as high as 102 S cm− 1 in the temperature range of 873–1223 K and it gradually decreased with the increasing amount of Fe substituted for Ni. The oxygen permeation rate was significantly enhanced by the Fe doping and it was found that the highest oxygen permeation rate (60 μmol min− 1 cm− 2) from air to He was achieved for x = 0.05 in Pr2Ni0.8 − xCu0.2FexO4. Since the chemical stability of the Pr2NiO4-based oxide is high, Pr2Ni0.75Cu0.2Fe0.05O4 can be used as the oxygen-separating membrane for the partial oxidation of CH4. It was observed that the oxygen permeation rate was significantly improved by changing from He to CH4 and the observed permeation rate reached a value of 225 μmol min− 1 cm− 2 at 1273 K for the CH4 partial oxidation.