Enhanced Performance of La2NiO4+δ Oxygen-Transporting Membranes Using Crystal Facet Engineering via Microemulsion-Based Synthesis

La2NiO4+δ nanorods, synthesized via reverse microemulsiona crystal facet engineering methodserved as building blocks for developing oxygen transport membranes. Comparisons were drawn with ceramic membranes derived from commercial La2NiO4+δ nanoparticles. The membrane manufacturing process involved either conventional sintering or the field-assisted sintering technique/spark plasma sintering. The microstructure analysis of the initial powders and the resulting ceramics was thoroughly assessed by X-ray diffraction, scanning and transmission electron microscopy as well as energy-dispersive X-ray spectroscopy. As a consequence of the reaction conditions, the nanorods possess an orthorhombic crystal structure, with LaOBr present as a minor phase. Furthermore, the surface structure of the La2NiO4+δ nanorods was discerned via selected area electron diffraction, revealing a composition of (001)o-type and (1 1̅ 0)o-type facets on the sides and (110)o-type facets at the end, with additional facets observed between these surfaces. Among the sintering techniques, spark plasma sintering demonstrated superior performance, when applied to La2NiO4+δ nanorods, as it effectively preserved their rod-like nanostructure during the sintering process. The resulting nanorod-derived La2NiO4+δ ceramics exhibited excellent oxygen permeation, largely due to the large proportion of orthorhombic (1 1̅ 0)o-type surfaces in the rod-shaped grains, which correspond to tetragonal (010)t and (0 1̅ 0)t surfaces. The (1 1̅ 0)o-type facets facilitated the oxygen surface exchange, leading to improved oxygen permeation fluxes between 1023 and 1123 K compared to membranes derived from nanoparticles.