NiCo2O4 particles with diamond-shaped hexahedron structure for high-performance supercapacitors.

Nickel cobalt oxide (NiCo 2 O 4 ) particles with a diamond-shaped hexahedral porous sheet structure are successfully synthesized by a facile hydrothermal method, followed by calcination in one step. NiCo 2 O 4 -I and NiCo 2 O 4 -II particles are prepared using the same method with different contents of urea (CO(NH 2 ) 2 ) and ammonium fluoride (NH 4 F). The different morphologies of the NiCo 2 O 4 -I and NiCo 2 O 4 -II particles illustrate that CO(NH 2 ) 2 and NH 4 F play an important role in crystal growth. To verify the influence of NH 4 F and CO(NH 2 ) 2 on the morphology of the NiCo 2 O 4 particles, the theory of crystal growth morphology is analyzed. The electrochemical measurements show that NiCo 2 O 4 particles exhibit a high specific capacitance. At a current density of 1.0 mA cm −2 , the mass specific capacitances of the NiCo 2 O 4 -I and NiCo 2 O 4 -II electrodes are 690.75 and 1710.9 F g −1 , respectively, in a 6 M KOH aqueous electrolyte. The specific capacitances of the NiCo 2 O 4 -I and NiCo 2 O 4 -II electrodes remain ∼95.95% and ∼70.58% of the initial capacitance values after 5000 cycles, respectively. According to the two-electrode test, the NiCo 2 O 4 -II//AC asymmetric electrodes exhibited an ultrahigh energy density of 64.67 Wh kg −1 at the power density of 12 kW kg -1 , demonstrating its excellent application potential as an electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]