Enhanced oxygen reduction of multi-Fe3O4@carbon core-shell electrocatalysts through a nanoparticle/polymer co-assembly strategy.

This paper reports a facile synthesis of multi-Fe3O4@carbon (mFe3O4@C) core-shell nanoparticles (NPs) using co-assembly of Fe3O4 NPs and polystyrene-b-poly(ethylene oxide) (PS-b-PEO) as a template. Slow solvent exchange leads to multiple tiny hydrophobic Fe3O4 NPs entrapped within PS-b-PEO micelles. After polydopamine coating and subsequent carbonization, a carbon shell encapsulating multiple Fe3O4 cores is obtained. The significant features of mFe3O4@C lie in the more active Fe3O4 sites and available free space within the carbon shell. As a result, the oxygen reduction performance of the resultant mFe3O4@C shows a higher onset potential than that of single Fe3O4@C. Meanwhile, mFe3O4@C exhibits a larger limiting current density (5.2 mA cm-2 at 1.0 V), long-time stability, and methanol tolerance compared to commercial Pt/C. The generality of the micellar immobilized NPs as a template is expected to boost the fabrication of various core-shell NPs for practical applications.