Tuning the ceria interfaces inside the dual phase oxygen transport membranes

Dual-phase oxygen transport membranes (DP-OTMs) offer a good alternative for the separation of oxygen from gas mixtures. As a promising candidate, the overall performance of the fluorite-spinel composite Ce_xGd_1-xO_2-δ-Fe_yCo_3-yO₄ (CGO-FCO) is often dominated by the behavior of the CGO-CGO grain boundaries (GBs), such as solute and non-solute segregations and structural disorders within the boundary. Due to the largely unknown atomistic GB environment, any attempt to control the GBs for an optimized membrane performance is still severely limited. In order to bridge this essential gap, utilizing advanced transmission electron microscopy (TEM) techniques, we quantified both atomistic and chemical structures at the CGO GBs inside the CGO-FCO DP-OTMs down to sub-nm scale. The atomic-site specific lattice distortions, elemental distributions, and valence state variations were found to be well confined within ∼2 nm around the GB, where a clear dependence on the structural coherence of individual GBs can be established. Our results further unraveled the complicated CGO GB environment inside real DP-OTMs, and paved the path towards optimized processing of various types of functional membranes.