Conformally deposited NiO on a hierarchical carbon support for high-power and durable asymmetric supercapacitors

Metal oxide based supercapacitors can provide much higher energy densities as compared with carbon-based ones. However, metal oxides usually suffer from low power densities together with poor cycle life, which is a big barrier for their practical applications. In this work, purposely confined NiO nanoparticles have been deposited uniformly on a three-dimensional graphite foam-carbon nanotube forest substrate, giving rise to a well-integrated free-standing electrode (GF-CNT[at]NiO) with strong synergetic effects generated from nickel oxide and the carbon support. The electrode with 57.6% mass content of NiO delivers a high specific capacity of 196.5 mA h g-1 and excellent cycling stability for 30 000 cycles. By coupling with a graphene-CNT paper anode, an asymmetric supercapacitor (GF-CNT[at]NiO//G-CNT) is assembled, which demonstrates excellent cycling ability (only 18.3% of capacitance drop after 30 000 cycles) and high power density (1.06-7.14 kW kg-1), suggesting its great promise for advanced supercapacitors.