▎ 摘　　要

NiCo2O4 nanospheres supported on nitrogen-doped graphene (NiCo2O4/NG) composite materials have been successfully synthesized via two-step hydrothermal routes followed subsequently thermal annealing process. The introduction of NiCo2O4 is ascribed to their higher conductivity comparing with single-metal oxides (Co3O4 and NiO). The nitrogen-doped graphene is chosen as the support material to load the metal oxides because of its large theoretical specific surface area and excellent conductivity. Especially, the pyrrolic nitrogen atoms could endow excellent electronic properties to graphene. The morphological characterizations reveal that NiCo2O4/NG nanospheres with the average size about 300 nm are uniformly located on the surface of nitrogen-doped graphene. The electrochemical measurements indicate that as-fabricated NiCo2O4/NG composites deliver a remarkable electrochemical property comparing with NiCo2O4 or NiCo2O4/graphene. The NiCo2O4/NG presents a high specific capacitance of 563.0 F g(-1) at 1 A g(-1), and over 90.5% of original capacitance is maintained after 5000 cycles, which reveal superior electrochemical performance and excellent cycle stability of NiCo2O4/NG composite electrode materials. Such results provide a promising strategy to design and fabricate innovative composite electrode materials for diverse energy storage devices. (C) 2019 Elsevier B.V. All rights reserved.