Phase decomposition of La2NiO4+δ under Cr- and Si-poisoning conditions

The influence of simultaneous Cr- and Si-poisoning on the oxygen exchange kinetics of La2NiO4+δ was studied at 800 °C in dry and humid O2/Ar atmospheres over a period of 4000 h by means of dc-conductivity relaxation measurements. Chemical and morphological changes of the La2NiO4+δ surface exposed to increasingly harsh ambient conditions were investigated using X-ray photoelectron spectroscopy (XPS) depth profiling, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDXS) and high-resolution scanning transmission electron microscopy with energy dispersive X-ray and electron energy loss spectroscopy (HR-STEM EDXS/EELS). In the presence of Cr/Si-sources and under dry conditions, La2NiO4+δ shows good stability for more than 1000 h. However, as soon as humidity is introduced into the system a strong decline of the oxygen exchange activity is observed. Post-test analyses reveal newly formed partially blocking Cr- and Si-rich secondary phases on the surface of La2NiO4+δ which impede the surface exchange of oxygen.