Stability and oxygen-storage characteristics of Al-substituted YBaCo4O7+δ

A series of Al-substituted YBa(Co1−xAlx)4O7+δ samples was synthesized and characterized with respect to the capability to store large amounts of oxygen at low temperatures (at 200–400 °C) and the phase decomposition upon heating under oxidizing conditions at higher temperatures (above 550 °C). It was revealed that increasing the Al-substitution level up to x≈0.10 boosts up the phase-decomposition temperature from ∼550 to ∼700 °C, while the unique oxygen absorption/desorption characteristics remain nearly the same as those of the pristine YBaCo4O7+δ phase. The maximum amount of excess oxygen absorbed by the Al-substituted YBa(Co1−xAlx)4O7+δ samples was determined to be as large as δ≈1.45 for x=0.10 (in 100 atm O2 at 320 °C). Isothermal annealing experiments carried out for the same x=0.10 phase at 300 °C revealed that it could be reversibly charged and discharged with 1.2 oxygen atoms per formula unit by switching the gas flow from N2 to O2 and vice versa.

Graphical abstractA small amount of aluminum replacing cobalt in YBaCo4O7+δ works efficiently for boosting up the phase-decomposition temperature (TD), but yet retains the unique low-temperature oxygen-storage characteristics of the phase.Figure optionsDownload full-size imageDownload as PowerPoint slide