Vertically/parallelly orientated growth of NiCo₂O₄ nanosheet onto surface of hierarchically N-doped porous carbon for improved supercapacitor

Here, hierarchically N-doped porous carbon (HPNC) with very high surface area was prepared by a facile one-pot pyrolysis of ethylenediaminetetraacetic acid tripotassium salt dihydrate used as the carbon/nitrogen source and pore activating agent. The NiCo₂O₄ nanosheets were vertically grown onto the surface of HPNC (V-NiCo₂O₄/HPNC) via a urea homogeneous precipitation method by a microwave heating. Whereas the parallelly orientated NiCo₂O₄/HPNC (P-NiCo₂O₄/HPNC) was fabricated by a usual water-bath heating. The loading content of V-NiCo₂O₄/HPNC was higher than that of the P-NiCo₂O₄/HPNC, thus resulting in the larger specific capacitance. V-NiCo₂O₄/HPNC exhibited the high specific capacity (434.8 F g^-1 at 1.0 A g^-1), good rate performance, cycle stability (capacitance retention of 103% at 5 A g^-1 after 1000 cycles) and lower resistance, owing to the synergistic advantages of HPNC and vertically orientated NiCo₂O₄ nanosheets, which provided high electrical conductivity, and effective electrolyte ions and electrons transport path.