Structural and chemical characterization and 3D modelling of metal oxide core-shell nanoparticles with complex morphology

Abstract

A wide variety of metal oxide manganite and ferrite core-shell nanoparticles (NPs) with adjustable composition were characterized by means of Transmission Electron Microscopy related tools in order to precisely understand their composition, the arrangement of the different chemical species and cation valence state variation along the nanoparticles. The nanoparticles were produced at low temperature and ambient atmosphere using a one-pot two-step synthesis protocol involving the cation exchange of Mn or Fe by Co or Ni in preformed Mn3O4 or Fe3O4 NPs, allowing the formation of a core shell structure. These nanoparticle systems present a complex 3D structure, which has been modelled with Rhodius software and simulated with the STEM-CELL packages, giving rise to a fine determination of the studied systems. Special attention has been paid on manganite – cobalt systems. By selecting the proper cobalt precursor, CoO crystallites could be simultaneously nucleated on the NP surface to form Mn3O4@CoMn2O4–CoO (Figure 1). In this latest case, heterostructured NPs exhibited improved performance and durability as bifunctional catalysts for the oxygen reduction and evolution reactions (ORR, OER) over commercial Pt and IrO2-based catalysts and over previously reported spinel electrocatalysts in alkaline solution.