Carbon dots decorated zinc cobaltite nanowires-assembled hierarchical arrays supported on nickel foam as binder-free electrodes for high performance supercapacitors

Abstract

Hierarchical and binder-free electrode materials with large electroactive sites and low contact resistance are benefit for electrochemical capacitors. Herein, this paper reports the binder-free and hierarchical ZnCo 2 O 4 arrays decorated with carbon dots (CDs/ZnCo 2 O 4 ) on nickel foam by hydrothermal route. The CDs/ZnCo 2 O 4 arrays exhibit the nanowires-assembled hierarchical grass-like structure. The outward directed nanowires yield high surface-to-volume ratio. The nanowires exhibit the average length of 1 μm and diameter of 50 nm. The specific capacitance of the CDs/ZnCo 2 O 4 can reach 1937 F/g higher than the 1192 F/g of bare ZnCo 2 O 4 at 1 A/g. And 78.5% capacitance retention rate is achieved while the current density increases from 0.5 to 8 A/g. 90% of the capacitance retention over 5000 charge-discharge cycles at 15 A/g indicates high cycling stability. These boosted electrochemical performances are attributed to the structural feature with exposed electroactive sites, high electrical conductivity assisted by CDs, and opened interspaces for electrolyte ion diffusion. Asymmetric two-electrode system assembled with CDs/ZnCo 2 O 4 and activated carbon delivers a high-energy density of 54.94 W h/kg at 425.3 W/kg and retains an energy density of 13.23 W h/kg at 6804 W/kg. This study provides a new approach to design high-performance electrode materials for supercapacitors. • Hierarchical ZnCo 2 O 4 arrays were decorated with carbon dots (CDs). • CDs/ZnCo 2 O 4 electrode exhibited 1937 F/g at 1 A/g higher than bare ZnCo 2 O 4 . • Assembled two-electrode system delivered 54.94 W h/kg at 425.3 W/kg.