Oxygen storage capacity and thermal stability of brownmillerite-type Ca2(Al1-xGax)MnO5+δ oxides

Abstract

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(Al1-xGax)MnO5+δ (0 ≤ x ≤ 1) with a brownmillerite-type structure were investigated. Ca2AlMnO5+δ can reversibly store/release a large amount of excess oxygen (~3.0 wt%) at low temperature (between 300 and 600 o C) under oxidative atmospheres. With the increasing Ga doping amount in Ca2(Al1-xGax)MnO5+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(Al1-xGax)MnO5+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(Al1-xGax)MnO5+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.

Tunable Oxygen Intake/Release Characteristics of Brownmillerite-Type Ca2AlMnO5+δ Involving Atomic Defect Formations

“…24−28 However, chemical substitutions often make negative impacts on the oxygen intake/ release kinetics due to weakened affinity to oxygen. 27,28 Therefore, it is desirable to tune the oxygen storage characteristics without chemical substitutions. Our preliminary experiments revealed that the properties of CAMO strongly depend on the synthesis condition.…”

“…Such a high operating temperature is an obstacle for practical uses because high-temperature processes would hinder the usage of metallic materials in the PSA apparatus. To lower the phase transformation temperature of CAMO, Sr-for-Ca and Ga-for-Al substitutions were previously attempted and found to work effectively. − However, chemical substitutions often make negative impacts on the oxygen intake/release kinetics due to weakened affinity to oxygen. , Therefore, it is desirable to tune the oxygen storage characteristics without chemical substitutions. Our preliminary experiments revealed that the properties of CAMO strongly depend on the synthesis condition.…”

Improvement of the Oxygen Storage/Release Speed of YBaCo4O7+δ Synthesized by a Glycine-Complex Decomposition Method

“…Therefore, it is necessary to investigate inexpensive, high efficiency, and excellent oxygen storage properties for these applications. Recently, a large number of OSMs have been actively investigated. − …”

Sr-Doped Ca2AlMnO5 + δ for Energy-Saving Oxygen Separation Process

“…Perovskites (ABO 3 ) and perovskite-like oxides have been studied as OSMs because of their stability as well as high oxygen deficiency or oxygen excess. In particular, perovskites, whose B sites are occupied by elements with easily changed valence, such as Mn, − Fe, − and Co ,, have been studied widely. OSMs used for oxygen separation by the PSA process need to be able to release stored oxygen in the presence of ambient oxygen rather than in a reducing atmosphere, in addition to having large oxygen storage capacity.…”