Evolution of Exsolved Nanoparticles on a Perovskite Oxide Surface during a Redox Process

To evaluate the self-regeneration feasibility of exsolved Co–Fe nanoparticles on the La_0.3Sr_0.7Cr_0.3Fe_0.6Co_0.1O_3−δ perovskite at intermediate operation temperature (700 °C), the evolution of surface morphology and particle phases during a redox process has been determined by scanning and transmission electron microscopy. Unlike the complete reincorporation of the exsolved metals back to the perovskite lattice at 800 °C during the reoxidation process, the transition-metal oxide remains on the surface as an intermediate phase because of a sluggish reincorporation rate at 700 °C. Although the transition-metal oxide particles grow and coarsen quickly in an oxidizing atmosphere, the nanoparticles could still be formed by a disintegration of the reduced spinel oxide in a reducing atmosphere. The hemispherical-like shape of the nanoparticles can be achieved by minimizing metallic surface energy and maintaining the strong metal–oxide interaction. The redispersion of Co–Fe nanoparticles completes the self-regeneration process at 700 °C. The exsolved nanoparticle size distribution is strongly affected by temperature but not by a redox process, which improves performance stability and reactivation at the relatively lower temperature during long-term operation