Oxygen storage capacity and thermal stability of brownmillerite-type Ca₂(Al_1-xGa_x)MnO_5+δ oxides

Understanding the oxygen uptake/release mechanism in oxygen storage materials is of great importance in the design of energy-related materials and their corresponding applications. In this work, the effects of Ga doping amount on the oxygen storage capacity and thermal stability of Ca₂(Al_1-xGa_x)MnO_5+δ (0 ≤ x ≤ 1) with a brownmillerite-type structure were investigated. Ca₂AlMnO_5+δ can reversibly store/release a large amount of excess oxygen (∼3.0 wt%) at low temperature (between 300 and 600 °C) under oxidative atmospheres. With the increasing Ga doping amount in Ca₂(Al_1-xGa_x)MnO_5+δ, these materials uptake less oxygen at higher temperature which can be attributed to the difficulty in the oxidation of tetrahedral GaO₄ blocks into octahedral GaO₆ blocks under 1 atm O₂. However, with the increasing of Ga-substitution amount, these Ca₂(Al_1-xGa_x)MnO_5+δ (0 ≤ x < 1) can start to uptake oxygen at lower temperatures during the cooling process under flowing O₂ due to the distorted structure. The results demonstrated that Ca₂(Al_1-xGa_x)MnO_5+δ (0 ≤ x < 1) can reversibly store/release large amounts of oxygen via just controlling the surrounding temperature and/or oxygen partial pressure but without using reductive gases, which would enable them great potentials in many applications.