Nickel cobaltite nanosheets strongly anchored on boron and nitrogen co-doped graphene for high-performance asymmetric supercapacitors.

Strongly coupled boron and nitrogen co-doped graphene (BN-G) hybrids with nickel cobaltite (NiCo2 O4 ) nanosheets (NCO/BN-G) were fabricated by a facile soft-chemical method for asymmetric supercapacitors with high-performance. The strong interaction between BN-G and NiCo2 O4 nanosheets are explored by various techniques. The effect of heteroatom doping on electrochemical properties of the hybrids is systematically investigated. The strong synergistic effect between NiCo2 O4 and BN-G leads to a specific capacitance of 106.5 mA h g-1 at the current density of 0.5 A g-1 and capacitance retention of 96.8% after 10 000 cycles at 5 A g-1 , much better than those of the pure NiCo2 O4 and its hybrid with N-doped graphene. Moreover, an asymmetric supercapacitor device, assembled with NCO/BN-G and activated carbon (NCO/BN-G//AC), exhibits a maximum energy density of 45.6 Wh kg-1 and an excellent cycling stability. The improved electrochemical performance of the NCO/BN-G hybrid is attributed to the good conductivity of BN-G and the synergistic effect between NiCo2 O4 nanosheets and BN-G combined together through a plane-to-plane contact mode.