Tunable Oxygen Intake/Release Characteristics of Brownmillerite-Type Ca₂AlMnO_5+δ Involving Atomic Defect Formations

Abstract

The oxygen intake/release characteristics were systematically studied for Ca2AlMnO5+δ samples synthesized under precisely controlled oxygen pressures. Both the oxygen storage capacity (OSC) and operating temperature were systematically lowered as the oxygen pressure in the firing atmosphere increased. Notably, the sample fired under a 1% O2 atmosphere exhibited sufficiently large OSC and superior oxygen intake/release kinetics to the pristine sample synthesized in an anaerobic condition. The high-angle annular dark-field scanning TEM observation revealed that the samples contain defects in their atomic arrangement when fired in oxygen-rich atmospheres. This result indicates that the oxygen intake/release characteristics of Ca2AlMnO5+δ are sensitive to the synthesis condition and widely tunable even without chemical substitutions.

New Triclinic Perovskite-Type Oxide Ba5CaFe4O12 for Low-Temperature Operated Chemical Looping Air Separation

“…From the isothermal TG data, theoretical values of the daily O 2 -gas productivity were estimated for Ba 4 CaFe 3 O 9.5 and Ba 5 CaFe 4 O 12 , together with some representative OSMs reported in the literature (see Figure and Table S5). The values were calculated based on the amount of oxygen reversibly stored and released during the isothermal TG run, with the reaction time required for a single TG cycle . The Ba 4 CaFe 3 O 9.5 and Ba 5 CaFe 4 O 12 materials in the present study mark record-high values of the O 2 -gas production rate of >2.4 m O2 3 kg OSM –1 day –1 .…”

“…The Ba 4 CaFe 3 O 9.5 and Ba 5 CaFe 4 O 12 materials in the present study mark record-high values of the O 2 -gas production rate of >2.4 m O2 3 kg OSM –1 day –1 . These values are indeed much higher than 0.81 m O2 3 kg OSM –1 day –1 for Sr 0.76 Ca 0.24 FeO 3−δ operating at 550 °C and 0.99 m O2 3 kg OSM –1 day –1 for the “modified” Ca 2 AlMnO 5+δ operating at 472 °C . It is worth pointing out that the Ba–Ca–Fe oxides can work at temperatures below 400 °C, much lower than those for the reference OSMs.…”

“…The values were calculated based on the amount of oxygen reversibly stored and released during the isothermal TG run, with the reaction time required for a single TG cycle. 25 The Ba 4 CaFe 3 O 9.…”

“…Such oxygen/vacancy-disordered oxides do not change their average crystal structure through oxygen content variations. In contrast, other types of OSMs, which undergo structural phase transformation induced by oxygen intake/release, have been developed, including YBaCo 4 O 7+δ , − Ca 2 AlMnO 5+δ , − and YMnO 3+δ . − These OSMs crystallize in intrinsically oxygen-deficient structures containing ordered 4- or 5-coordinated TM sites. Excess oxygen atoms are incorporated into positions adjacent to such “coordinatively unsaturated” sites, accompanied by an increase in the oxidation number of TMs.…”

Oxygen Separation Performance of Ca₂AlMnO_5+<i>δ</i> as an Oxygen Storage Material for High-Temperature Pressure Swing Adsorption

“…Ca 2 AlMnO 5 + δ (CAMO) is one of the prominent OSM candidates other than Fe-based perovskites. CAMO is capable of storing and releasing up to 3.3 wt% of oxygen (Δδ = 0.5) according to the following oxygen storage/ release reaction: 14,15) Ca AlMnO + 2 O Ca AlMnO Although various studies on CAMO as the OSM have been reported so far, 14,[16][17][18][19][20][21][22] the HT-PSA test results of CAMO have not been reported. The HT-PSA test can reveal issues that do not manifest in individual characteristic studies, such as the oxygen storage and release reaction rates, which are not taken into account in equilibrium composition measurements, and the temperature change of the OSM owing to reaction heat, which is controlled during thermogravimetric measurements.…”