Nanostructured carbons containing FeNi/NiFe₂O₄ supported over N-doped carbon nanofibers for oxygen reduction and evolution reactions

Non-precious metal-based electrocatalysts on carbon materials with high durability and low cost have been developed to ameliorate the oxygen-reduction reaction (ORR) and oxygen-evolution reaction (OER) for electrochemical energy applications such as in fuel cells and water electrolysis. Herein, two different morphologies of FeNi/NiFe₂O₄ supported over hierarchical N-doped carbons were achieved via carbonization of the polymer nanofibers by controlling the ratio of metal salts to melamine: a mixture of carbon nanotubes (CNTs) and graphene nanotubes (GNTs) supported over carbon nanofibers (CNFs) with spherical FeNi encapsulated at the tips (G/CNT@NCNF, 1 : 3), and graphene sheets wrapped CNFs with embedded needle-like FeNi (GS@NCNF, 2 : 3). G/CNT@NCNF shows excellent ORR activity (on-set potential: 0.948 V vs. RHE) and methanol tolerance, whilst GS@NCNF exhibited significantly lower over-potential of only 230 mV at 10 mA cm^-2 for OER. Such high activities are due to the synergistic effects of bimetallic NPs encapsulated at CNT tips and N-doped carbons with unique hierarchical structures and the desired defects.