Electrical conductivity and oxygen transfer in gadolinia-doped ceria (CGO)–Co3O4−δ composites

Dense, mixed-conducting ceramic membranes can be used for separation of oxygen from air. Dual-phase composites are an interesting way to obtain mixed conductivity because it is easy to tailor the electrical and transport properties by varying the fractions of the ionic and electronic components. In this study, mixed-conducting Ce0.8Gd0.2O2−δ (CGO)–Co3O4−δ composites were fabricated with density about 95% theoretical values. The solubility of Co3O4−δ in CGO was found to be lower than 1 mol% (or 1.6 vol.%). The total conductivity of the CGO–Co3O4−δ composites increased with increasing Co3O4−δ content. A microstructure with two interconnected phases was obtained for a Co3O4−δ content above 10 mol% (or 15 vol.%). Isotopic exchange depth profiling (IEPD)/secondary ion mass spectrometry (SIMS) method was used to investigate the oxygen diffusion and surface exchange reaction in the composites. The diffusivities of the composites were almost constant within the experimental error with significantly enhanced surface exchange kinetics by adding Co3O4−δ to CGO.