Preparation and the superior oxygen permeability of a new CO2-resistant Ruddlesden–Popper composite oxide Pr2Ni0.9Mo0.1O4+δ

Abstract

Dense Pr2NiO4+δ (PNO) and Pr2Ni0.9Mo0.1O4+δ (PNM) hollow fiber membranes were prepared by phase inversion/sintering method. Results of XRD analysis suggest that both PNO and PNM materials possess orthorhombic Ruddlesden-Popper phase, furthermore, PNM also contains two impurity phases, i.e. higher order Ruddlesden-Popper phase Pr4Ni3O10-δ′ and fluorite phase PrO2-δ″. Thermal expansion coefficients of PNO and PNM materials are very close to those of the solid electrolytes GDC and SDC. Oxygen permeation fluxes of both membranes increase with rising temperature and flow rate of helium gas. Oxygen permeability of the PNM membrane is better than that of undoped PNO material, which is confirmed by apparent activation energies calculated from Arrhenius plots with two line segments of both membranes, 38.67 kJ mol−1 (high temperature segment) and 97.83 kJ mol−1 (low temperature segment) for PNM vs. 57.95 kJ mol−1 and 115.81 kJ mol−1 for PNO. First-principles method were adopted to calculate the formation energies of four kinds of oxygen defects in PNO, which demonstrate that the formation of interstitial oxygen defects is much more favorable than two kinds of oxygen vacancy defects, implying that the oxygen transfer in PNO takes interstitial oxygen mediated transport mechanism instead of oxygen vacancy mechanism. In addition, the test results of permeation stability indicate that the PNM composite is a promising CO2-tolerant material as oxygen separation membrane, SOFC cathode, etc.