Fabrication of a MnCo2O4/gadolinia-doped Ceria (GDC) Dual-phase Composite Membrane for Oxygen Separation

A dual-phase ceramic membrane consisting of gadolinium-doped ceria (GDC) as an oxygen ion conducting phase and MnCo₂O₄ as an electron conducting phase was fabricated by sintering a GDC and MnCo₂O₄ powder mixture. The MnCo₂O₄ was found to maintain its spinel structure at temperatures lower than 1200℃. (Mn,Co)(Mn,Co)O4 spinel, manganese and cobalt oxides formed in the sample sintered at 1300℃ in an air atmosphere. XRD analysis revealed that no reaction phases occurred between GDC and MnCo₂O₄ at 1200℃. The electrical conductivity did not exhibit a linear relationship with the MnCo₂O₄ content in the composite membranes, in accordance with percolation theory. It increased when more than 15 vol% of MnCo₂O₄ was added. The oxygen permeation fluxes of the composite membranes increased with increasing MnCo₂O₄ content and this can be explained by the increase in electrical conductivity. However, the oxygen permeation flux of the composite membranes appeared to be governed not only by electrical conductivity, but also by the microstructure, such as the grain size of the GDC matrix.