A template-free route to a Fe3O4-Co3O4 yolk-shell nanostructure as a noble-metal free electrocatalyst for ORR in alkaline media

This paper reported a facile template-free route to prepare hierarchical Fe3O4-Co3O4 yolk-shell nanostructures. These highly porous architectures, with a diameter of about 2 mm, were assembled from Co3O4 flower-like shells and Fe3O4 sphere core. A series of experiments with different conditions were carried out to determine the key factors in this typical solvothermal synthesis that led to the formation of the obtained yolk-shell nanostructures, and a possible growth mechanism was proposed. Sequentially, some other similar metal oxide nanostructures were also obtained in this way. Importantly, the obtained Fe3O4-Co3O4 yolk-shell nanostructures exhibit excellent electrocatalytic ORR performance. The half-wave potential of the yolk-shell nanostructures is about 5 and 80 mV positive-shifted compared to that of the independent Co3O4 and Fe3O4 nanoparticles. The current density of O-2 reduction for the Fe3O4-Co3O4 yolk-shell nanostructures is also much higher than that of Co3O4 and Fe3O4 nanoparticles. The enhanced electrocatalytic performance for Fe3O4-Co3O4 yolk-shell nanostructures may make them available to be an efficient and cheap noble-metal free cathodic catalyst for PEMFCs.