Hydrothermal Synthesis of NiCo2O4 @NiCo2O4 Core-Shell Nanostructures Anchored on Ni Foam for Efficient Oxygen Evolution Reactions Catalysts

NiCo2O4@NiCo2O4 core-shell nanostructures anchored on Ni foam (NF) are synthesized by the hydrothermal and subsequent calcination process. In these structures, NiCo2O4 nanosheets are coated on NiCo2O4 nanocones, which are decorated on the surface of conductive NF. As an oxygen evolution reaction catalyst, the NiCo2O4@NiCo2O4 exhibits low overpotential of 440 mV at the current density of 100 mA cm−2. Furthermore, the composite shows outstanding long-term stability during 12 h continuous operation. Electrochemical impedance spectroscopy (EIS) reveals that the charge transfer resistance of NiCo2O4@NiCo2O4 is much smaller than other composites. The results reveal that the composite exhibits superior activity for OER in contrast to individual NiCo2O4 nanosheets or NiCo2O4 nanocones, which are attributed to the NiCo2O4@NiCo2O4 composite and integrate multiple advantages of nanostructures, abundant catalytic sites and outstanding stability.