Growth of cobalt–nickel layered double hydroxide on nitrogen-doped graphene by simple co-precipitation method for supercapacitor electrodes

Nitrogen-doped graphene/Co–Ni layered double hydroxide (RGN/Co–Ni LDH) is synthesized by a facile co-precipitation method. Transmission electron microscopy images indicated that the formation of Co–Ni(OH)₂ nanoflakes with the good dispersion anchored on the surfaces of the nitrogen-doped graphene sheets. The nitrogen-doped graphene composites delivered the enhanced electrochemical performances compared to the pure Co–Ni LDH due to the improved electronic conductivity and its hierarchical layer structures. The high specific capacitance of 2092 F g⁻¹ at current density of 5 mA cm⁻² and the rate retention of 86.5% at current density of 5–50 mA cm⁻² are achieved by RGN/Co–Ni LDH, higher than that of pure Co–Ni LDH (1479 F g⁻¹ and 76.5%). Moreover, the two-electrode asymmetric supercapacitor, with the RGN/Co–Ni LDH composites as the positive electrode and active carbon as the negative electrode material, exhibits energy density of 49.4 Wh kg⁻¹ and power density of 101.97 W kg⁻¹ at the current density of 5 mA cm⁻², indicating the composite has better capacitive behavior.