Core-shell nanowires of NiCo2O4@α-Co(OH)2 on Ni foam with enhanced performances for supercapacitors.

The composites of NiCo2O4 with unique structures are extensively explored as promising electrodes. In this work, core-shell structured nanowires anchored on nickel foam are synthesized by the hydrothermal synthesis of NiCo2O4 as core and subsequent electrodeposition of α-Co(OH)2 as shell. The core-shell composites exhibit enhanced electrochemical performances ascribing to the synergistic reactions from both materials, showing higher specific capacitance than any single component. By changing the deposition time, the mass loading of α-Co(OH)2 can be easily controlled. The electrochemical performances of the hybrid electrodes are diverse with the mass loading of Co(OH)2. The optimized hybrid electrode with 3 mins electrodeposition exhibits the highest specific capacitance (1298 F g-1 at 1 A g-1) among all electrodes. The redox reaction is a main contributor to the total specific capacitance through electrochemical kinetics analysis. An asymmetric supercapacitor assembled by the optimized material as positive electrode and activated carbon as negative electrode can achieve a relatively high energy density of 39.7 Wh kg-1 at a power density of 387.5 W kg-1 (at 0.5 A g-1) in a voltage of 1.55 V.