Atomistic Insight into the Redox Reactions in Fe/Oxide Core–Shell Nanoparticles

Modern technological pressure for property-directing structural design of Fe/oxide core–shell nanoparticles (NPs) requires the basic understanding of the formation mechanisms and the ability to effectively tune the structures. In this work, in-depth transmission electron microscopy characterization reveals the formation of an Fe/Fe3O4 core–shell structure when iron NPs were oxidized at room temperature. More importantly, we present the first atomically resolved dynamical images showing the redox reactions in Fe/oxide NPs at high temperature (400–600 °C). The real-time videos show the unambiguous evidence of the reduction and incorporation of oxygen species along the specific interfaces, leading to the reduction of Fe3O4 to FeO and oxidation of Fe to Fe3O4, which are further investigated based on the theoretical calculations. Meanwhile, it is found that the passive Fe3O4 shell may provide the oxygen ions for the further oxidation of the Fe core at high temperature. These findings contribute to a comprehensive scenario for the structural evolution in metal/oxide nanostructures for improved device design and modeling.