The in situ generated emerging phase inside dual phase oxygen transport membranes

The in situ generated emerging phase inside the dual-phase oxygen transport membranes (DP-OTMs) plays a crucial role in boosting the overall performance of DP-OTMs. However, its detailed structure and properties are still not fully understood. Utilizing advanced transmission electron microscopy (TEM) techniques, the emerging phase Gd_xCe_1-xFe_yCo_1-yO_3-δ (GCFCO) inside the Ce_xGd_1-xO_2-δ-FeCo₂O₄ (CGO-FC2O) OTMs was successfully characterized at the atomic scale. The newly formed GCFCO is primarily surrounded by the CGO, and contributes to a significant reduction of non-solute segregation at the CGO grain boundaries. Electronic characteristics of the GCFCO shows a sensitive dependence on its chemical composition, including the valence state of Ce and Fe as well as the oxygen vacancies. Additional CGO-GCFCO interfaces were introduced, where almost intact crystal structures were observed with slight Gd and Co segregation ∼1 nm at the edges. Approaching the interface, on the CGO side, only a minimum drop of the Ce valence was determined. On the GCFCO side, mixed Ce³⁺ and Ce⁴⁺ are partially occupying the Gd sites, while Fe and Co valence stay constant until the edge. Our study provides novel insight into the phase information within CGO-FC2O composites, which paves the path towards superior performance of various DP-OTMs.