A Facile approach to NiCoO2 intimately standing on nitrogen doped graphene sheets by one-step hydrothermal synthesis for supercapacitors

Novel composites based on cubic binary nickel cobaltite oxide intimately standing on nitrogen doped reduced graphene sheets (NRGO-NiCoO2) were prepared by a simple one step hydrothermal synthesis. The results showed that the highly crystalline NiCoO2 nanoparticles with a uniform size were homogeneously distributed on nitrogen-doped reduced graphene sheets (NRGO). The homogeneous composites combined NiCoO2, which has high specific capacitance, and NRGO, which has efficient electronic conductivity, to consequently yield low resistance conduction between metal oxides and graphene due to a barrier-free contact. The synergistic effect of NRGO substrates and NiCoO2 nanoparticles promoted the electrochemical performance of the composites. The electrochemical properties of NRGO-NiCoO2 can be easily tuned by altering the amount of nitrogen-composed reducer. The NRGO-NiCoO2 composites exhibited a remarkable specific capacitance of 508 F g(-1) at 0.5 A g(-1), an excellent rate performance in cyclic voltammetry test (from 5 to 90 mV s(-1)) and good galvanostatic charge-discharge measurements (from 0.5 to 20 A g(-1)). The capacitance was maintained at 93% of the original value even after 2000 cycles. The flexible devices were assembled, which possessed a specific capacitance of 58 F g(-1) at 0.5 A g(-1). This facile one-step strategy is an effective method for developing excellent supercapacitor electrodes.