Rapid oxygen storage and release with Brownmillerite-structured Ca2AlMnO5

Abstract Brownmillerite-structured Ca2AlMnO5 is inexpensive and capable of rapid oxygen storage and release. This study focused on improving the oxygen storage/release rate of Ca2AlMnO5, which is essential for its application in practical oxygen production systems. Two approaches were investigated for improving the oxygen-trapping ability of Ca2AlMnO5: heat treatment for 2 h and 24 h after solution combustion synthesis (SCS) and the addition of Pt nanoparticles as a catalyst. Noticeably, crystalline Ca2AlMnO5 was formed after heat treatment at 1250 °C for at least 2 h. For the 2-h heat treatment, the average particle size of Ca2AlMnO5 was 11.4 μm, while that for the 24-h treatment was 18.9 μm. This reduction in the particle size increases the oxygen storage/release rate because of the relatively short diffusion distance within the particles. The oxygen storage rate increased with the addition of Pt nanoparticles because the nanoparticles were distributed across the surface and acted as catalyst. This catalyst accelerated the oxygen-evolution reaction by activating the surface reactions between oxygen ions and the Ca2AlMnO5 particles. The short 2-h heat treatment prevented the Pt nanoparticles from aggregating. When the Pt nanoparticle addition was implemented in combination with the 2-h heat treatment, the storage and release rates were drastically improved, i.e., by 2.5 and 6.1 times, respectively, compared with the sample after 24-h heat treatment without Pt nanoparticles. The oxygen storage/release rate remained constant even after repeated use at 550 °C, for over 25 cycles. Furthermore, Ca2AlMnO5 suffered no surface damage, and none of the Pt nanoparticles re-agglomerated after this test, further indicating the durability of the treated material.