Flower-like NiO with a Hierarchical and Mesoporous Structure for Supercapacitors

Hierarchical porous nickel oxide (NiO) has been synthesized through an ethanol-based hydrothermal method followed by a sintering process. The effects of hydrothermal duration on morphology, crystalline structure, and electrochemical performance are studied. With the prolongation of hydrothermal duration, the as-prepared NiOs appear in the form of scattered nanoflakes, then flower-like porous balls, and then solid microballs. In this period, poly-crystallization and re-crystallization are observed successively. It seems 120 minutes is suitable to form hierarchical NiO, 2m mesoporous balls composed of nanoflakes in all directions. The duration shows significant influence on charge-storage characteristics including reversibility, capacitance, and cyclic stability. The sample exhibits 678.4F/g at 1A/g discharge current density and maintains 94.8% retention after 5000 cycles, suggesting a great prospect of the hierarchical NiO to be used as an electrode material for supercapacitors.