Encapsulation of Ni/Fe3O4 heterostructures inside onion-like N-doped carbon nanorods enables synergistic electrocatalysis for water oxidation.

The rational modulation of composition and structure is critical for the development of robust and efficient oxygen evolution reaction (OER) catalysts for water splitting. In this study, an onion-like N-doped carbon nanorods hybrid (denoted as ONC) with encapsulated Ni/Fe3O4 heterostructures has been fabricated by the pyrolysis of an NiFe-based coordination polymer under a N2 atmosphere. The nanorod-like morphology is transferred from the polymer to the hybrids and generates ONC nanolayers encapsulated with core-shell Ni/Fe3O4 nanostructures. The synergistic effects between the ONC layers and the encapsulated Ni/Fe3O4 heterostructures result in high electronic conductivity due to the nitrogen-doped carbon with an appropriate level of defects and enlarged electrochemical surface area due to the well-defined mesoporous morphology. Compared with Ni@ONC, Fe3O4@ONC, NiFe2O4 and commercial RuO2 electrocatalysts, the as-prepared Ni/Fe3O4@ONC exhibits extraordinary electrocatalytic activity for water oxidation with an overpotential of merely 296 mV at 10 mA cm-2 and a small Tafel slope of 61 mV dec-1. This Ni/Fe3O4@ONC OER catalyst highlights the great potential of integrating hetero-composite nanocatalysts with hetero-atom doped nanocarbon supports for the development of high-performance electrocatalysts for renewable energy applications.