Effect of doping, microstructure, and CO2 on La2NiO4+δ-based oxygen-transporting materials

Abstract Alkaline earth-free La 2 NiO 4+ δ based materials were synthesized by a sol–gel method and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques as well as oxygen permeation experiments. Effects of doping the nickel position with a variety of cations (Al, Co, Cu, Fe, Mg, Ta, and Zr) were investigated with regards to oxygen flux and microstructure. Doping was always found to diminish the oxygen flux as compared to the reference composition. However, larger grains, which were achieved by longer annealing times at 1723 K have a minor negative impact on oxygen permeation flux in case of La 2 NiO 4+ δ and La 2 Ni 0.9 Fe 0.1 O 4+ δ system. Mossbauer spectroscopy shows that the iron-doped system exhibits a secondary phase, which was identified by high-resolution transmission electron microscopy (HRTEM) as a higher Ruddlesden-Popper phase. In-situ XRD in an atmosphere containing 50 vol% CO 2 and long-term oxygen permeation experiments using pure CO 2 as the sweep gas revealed a high tolerance of the materials towards CO 2 .