NiCo2O4@rGO hybrid nanostructures on Ni foam as high-performance supercapacitor electrodes
Pseudocapacitors store energy on/near the surface of electrode materials through redox reactions, whose capacitive activity thus depends on the electronic states of the surface and interface, and electronic conductivity of the electrode materials. Here, we report a simple strategy to prepare the hybrid nanostructure of NiCo2O4@rGO with the controllable composition by depositing graphene oxide (GO) on the NiCo2O4 scaffold combined with chemical reduction. By combining NiCo2O4 mesoporous nanosheets with reduced graphene oxide (rGO), the hybrid electrode shows significant improvement in electrical conductivity, as well as more electrochemically active sites and short transport path lengths for both electrons and ions. Moreover, resulting from the Schottky electric field at the interface of NiCo2O4 and rGO, NiCo2O4 exhibits superior electron collection efficiency, thus contributing to the redox reactions on/near the surface of NiCo2O4. Benefiting from the rational structural features and excellent electrical conductivity, the designed NiCo2O4@rGO hybrid electrode demonstrates high specific capacitance (3.6 F cm−2 at a current density of 5 mA cm−2), good rate capability and superior cycling stability (90% of the initial capacitance can be retained after 2000 charge/discharge cycles). This work provides a new strategy for high-performance supercapacitor electrodes by combining capacitive (especially carbons) and faradaic (redox electroactive) materials.