Encapsulation of Co O Nanocone Arrays via Ultrathin NiO for Superior Performance Asymmetric Supercapacitors.

Designing of multicomponent transition metal oxide system through the employment of advanced atomic layer deposition (ALD) technique over nanostructures obtained from wet chemical process is a novel approach to construct rational supercapacitor electrodes. Following the strategy, core-shell type NiO/Co O nanocone array structures are architectured over Ni-foam (NF) substrate. The high-aspect-ratio Co O nanocones are hydrothermally grown over NF following the precision controlled deposition of shell NiO considering Co O nanocone as host. NiO thickness of 5 nm exhibits the highest specific capacity of 1242 C g (2760 F g ) at current density 2 A g , which is greater than pristine Co O @NF (1045.8 C g or 2324 F g ). The rate capability with 5 nm NiO/Co O @NF nanocone structures is about 77% whereas Co O @NF retains 46 % of capability at 10 A g . The ultrathin ALD 5 nm NiO accelerates both rate capability and 95.5% cyclic stability after 12 000 charge-discharge cycles. An asymmetric device fabricated between 5 nm NiO/Co O @NF (positive) || activated carbon (negative) achieves an energy density of 81.45 Wh kg (4268 W kg ) with good cycling device stability. Additionally, LEDs can be energized by two ASC device in series. This work opens the path in both advanced electrode material and surface modification of earth-abundant systems for efficient and real-time supercapacitor applications.