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

La<inf>2</inf>NiO<inf>4+δ</inf> 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 La<inf>2</inf>NiO<inf>4+δ</inf> 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 La<inf>2</inf>NiO<inf>4+δ</inf> nanorods was discerned via selected area electron diffraction, revealing a composition of (001)<inf>o</inf>-type and (1Formula Presented0)<inf>o</inf>-type facets on the sides and (110)<inf>o</inf>-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 La<inf>2</inf>NiO<inf>4+δ</inf> nanorods, as it effectively preserved their rod-like nanostructure during the sintering process. The resulting nanorod-derived La<inf>2</inf>NiO<inf>4+δ</inf> ceramics exhibited excellent oxygen permeation, largely due to the large proportion of orthorhombic (1Formula Presented0)<inf>o</inf>-type surfaces in the rod-shaped grains, which correspond to tetragonal (010)<inf>t</inf> and (0Formula Presented0)<inf>t</inf> surfaces. The (1Formula Presented0)<inf>o</inf>-type facets facilitated the oxygen surface exchange, leading to improved oxygen permeation fluxes between 1023 and 1123 K compared to membranes derived from nanoparticles.