One-step synthesis and characterization of La₂NiO _4+δ mixed-conductive oxide for oxygen permeation

A one-step process for the synthesis of La₂NiO _4+δ (LNO) mixed-conductive oxide was reported. During the process, LNO powders were synthesized via the combustion of mixtures with the desired metal ions as cation precursors and glycine as fuel. X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometry, and specific surface area analysis were used to characterize the crystal structures, morphologies, sintering behavior, and surface area of the LNO powders. The effect of the fuel ratio (φ) on the crystal structures of LNO oxide was studied to reveal the optimal synthesis conditions. It was determined that almost-pure LNO oxide with a K2NiF4-type phase could be achieved when $ = 1.2 without calcination steps. The synthesized LNO powders had good sintering properties, and the membranes derived from the powders could become dense after sintering in air at 1423 K for 5 h. The LNO powders possessed more interstitial oxygen ions in the rock-salt layers of LNO lattice than those derived from the traditional solid-state reaction (SSR) method. The oxygen permeability of the LNO membrane was examined by a high-temperature oxygen permeation measurement. The oxygen permeation flux (at 1173 K and the oxygen partial pressure gradient is 0.21 × 10⁵/1 × 10² Pa) of the LNO membrane originated from combustion process was 1.5 × 10^-7 mol cm ^-2 s^_1, which was 1.5 times greater than that of the SSR-derived membrane.