Evaluation of BaY1−Pr Mn2O5+δ oxides for oxygen storage technology

Abstract

Crystal structure and oxygen storage properties of A-site ordered BaY1 − xPrxMn2O5 + δ (x = 0, 0.25, 0.5, 0.75 and 1) perovskite-type oxides are reported, showing almost complete and reversible change (Δδ > 0.94 mol mol− 1) occurring between fully reduced BaY1 − xPrxMn2O5 and oxidized BaY1 − xPrxMn2O6 during reduction in 5 vol.% H2 in Ar atmosphere and oxidation in air at 500 °C. All reduced compounds, as well as oxidized ones for x ≥ 0.5 possess tetragonal structure with P4/nmm (or P4/mmm for BaPrMn2O6) symmetry at room temperature. In the case of BaY0.75Pr0.25Mn2O6 and BaYMn2O6, good Rietveld refinements of XRD data were obtained assuming either monoclinic P121 or triclinic P-1 symmetry. The oxidation process causes a significant decrease of unit cell volume, which is additionally linearly dependent on average ionic radius of Y1 − xPrx. Due to a higher molar mass, an increasing Pr content causes a decrease of reversible oxygen storage capacity; nevertheless, Pr-containing materials show improved reduction rate and oxidize at lower temperatures. The optimized BaY0.75Pr0.25Mn2O5-BaY0.75Pr0.25Mn2O6 system showed very stable performance for 50 cycles. The obtained results indicate that by an appropriate chemical modification, it is possible to enhance oxygen storage-related properties of BaY1 − xLnxMn2O5 + δ (Ln — lanthanides) oxides, and such materials are promising for oxygen storage technology application.