A determination of the oxygen non-stoichiometry of the oxygen storage material YBaMn2O5+

Abstract

Keywords:Oxygen storage material Double perovskite oxide Yttrium barium manganese oxide Oxygen non-stoichiometry a b s t r a c tThe A-site ordered double-perovskite oxide, YBaMn 2 O 5 þ δ , has been of recent interest for possible application as an oxygen storage material. In the present study, the oxygen non-stoichiometry of YBaMn 2 O 5 þ δ has been determined as a function of pO 2 at 650, 700 and 750°C by Coulometric titration at near-equilibrium conditions. The results confirm that this perovskite oxide has three distinct phases on oxidation/reduction with δE0, 0.5 and 1. The stabilities of the YBaMn 2 O 5 þ δ phases span a wide range of oxygen partial pressures (∼10 À 20 rpO 2 (atm) r ∼1 ) depending on temperature. The phases interconvert at higher pO 2 values at higher temperatures. The partial molar free energies (Δμ O ) corresponding to the oxidation of YBaMn 2 O 5 to YBaMn 2 O 5.5 and of YBaMn 2 O 5.5 to YBaMn 2 O ∼6 were determined. The value of Δμ O in both oxidation steps becomes less negative with increasing temperature. At some T and pO 2 conditions, YBaMn 2 O 5 þ δ is unstable with respect to decomposition to BaMnO 3 À δ and YMnO 3 . This instability is anticipated from the previous studies of the synthesis of YBaMn 2 O 5 þ δ but is more apparent in the present experiments which are necessarily slow in order to achieve equilibrium with respect to the oxygen content.

Oxygen storage properties and catalytic activity of layer-ordered perovskites BaY1−Gd Mn2O5+

“…However, for assumed larger weight changes, the E a values are similar. The results support known fact that the mechanism of the oxygen release changes on reduction, and is essentially of a two-phase type with a strong tendency of formation of the oxygen vacancy-ordered BaLnMn 2 O 5.5 phase [27]. Log(T/t) vs. 1/T coordinates were chosen instead of the standard Arrhenius ones, as they are representative for systems with ionic conduction, in which mobility of the charge carriers μ depends on their charge q, diffusion coefficient D and temperature: μ = qD/k b T (k b -Boltzmann constant).…”

Oxygen separation from air by the combined temperature swing and pressure swing processes using oxygen storage materials Y1−x(Tb/Ce)xMnO3+δ

“…Because the released oxygen recombines with hydrogen to form water, these OSMs are not applicable for the oxygen production. While the usage of inert gas for reduction is possible in many cases, the slow kinetics of the process limits the practical application [22].…”

Rare earth barium cobaltites: potential candidates for low-temperature oxygen separation

“…These preferential vacancy channels give an enhanced oxide ion transport in these materials making them applicable in solid oxide fuel cells [2] and oxygen transport membranes [25]. As mentioned earlier, manganese based rare earth barium oxides have been studied extensively in the literature for oxygen storage applications [17,19,20]. Only limited studies on cobalt based rare earth barium oxides are available in the literature, which are inclined towards high temperature (> 973 K) membrane separation [25,26] or cathodes for solid oxide fuel cells [2].…”

“…A number of new oxygen storage materials have been discovered in recent years [6,[9][10][11][12][13][14][15][16][17][18][19][20]. The oxygen intake/ release in these non-stoichiometric oxygen storage oxides takes place through the following steps [21], (1) oxygen molecules are diffused to the surface, (2) dissociative adsorption through electron transfer, (3) diffusion of the oxide ions from surface to the lattice through an activated hopping mechanism.…”

“…Among the different perovskite and double perovskite oxides studied, A-site ordered double perovskites [ (RE)BaB 2 O 6−x ] have been shown to have low oxidation temperatures, 373-573 K [16,17,20]. Of the B-site cations Mn, Co or Fe, the manganese based ones being the most studied system because of the widest variation in oxygen content [16,17,19,20]. The range of non-stoichiometry in these materials varies between 0 < x < 1, depending upon the rare earth cation [2] and synthesis conditions [23,24].…”