Asymmetric supercapacitors based on nano-architectured nickel oxide/graphene foam and hierarchical porous nitrogen-doped carbon nanotubes with ultrahigh-rate performance

A pulsed laser deposition process using ozone as an oxidant is developed to grow NiO nanoparticles on highly conductive three-dimensional (3D) graphene foam (GF). The excellent electrical conductivity and interconnected pore structure of the hybrid NiO/GF electrode facilitate fast electron and ion transportation. The NiO/GF electrode displays a high specific capacitance (1225 F g(-1) at 2 A g(-1)) and a superb rate capability (68% capacity retention at 100 A g(-1)). A novel asymmetric supercapacitor with high power and energy densities is successfully fabricated using NiO/GF as the positive electrode and hierarchical porous nitrogen-doped carbon nanotubes (HPNCNTs) as the negative electrode in aqueous KOH solution. Because of the high individual capacitive performance of NiO/GF and HPNCNTs, as well as the synergistic effect between the two electrodes, the asymmetric capacitor exhibits an excellent energy storage performance. At a voltage range from 0.0 to 1.4 V, an energy density of 32 W h kg(-1) is achieved at a power density of 700 W kg(-1). Even at a 2.8 s charge-discharge rate (42 kW kg(-1)), an energy density as high as 17 W h kg(-1) is retained. Additionally, the NiO/GF//HPNCNT asymmetric supercapacitor exhibits excellent cycling durability, with 94% specific capacitance retained after 2000 cycles.