A hybrid supercapacitor containing NiO microflowers as cathode material with enhanced energy storage performance

The NiO microflowers electrode material was synthesized through a simple and low-cost hydrothermal method using hexamethylenetetramine (HMTA) to provide hydroxide ions for the formation of corresponding precursors. On this basis, the effect of HMTA dosage on the morphology and electrochemical performance of nickel oxide was investigated. Two kinds of NiO powdered materials with distinct morphologies were successfully prepared. The NiO microflowers demonstrated a larger specific surface area (SSA, 142.43 m² g^-1) and a higher specific capacity (C_s) of 661.4 C g^-1. While the NiO microspheres possessed smaller SSA of 104.3 m² g^-1 and inferior C_s of 594.6 C g^-1. The NiO materials were employed as the cathode and activated carbon (AC) as the anode to assemble hybrid supercapacitor (HSC), which was expressed as NiO microflowers//AC and NiO microspheres//AC, respectively. Compared with the 53.5 W h kg^-1 energy density (ED) of NiO microspheres//AC, the NiO microflowers//AC achieved a higher ED of 55.4 W h kg^-1. Both HSCs showed over 90 % capacity retention after 4000 cycles at 10 A g^-1, indicating that the two HSCs exhibited excellent cyclic lifespan. It suggests that the NiO electrode materials in this study show promising potential for electrochemical energy storage application. The current synthesis approach demonstrates notable advantages including simplicity, time and energy saving, and may be straightforwardly employed to prepared other electrode materials with controlled morphologies and superior electrochemical performance.