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

Abstract

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.