Ultrathin porous NiO nanoflake arrays on nickel foam as binder-free electrodes for supercapacitors

NiO nanopowders and NiO/nickel foam (NF) hybrid were synthesized by microwave hydrothermal method and the following heating process. NiO nanopowders show the morphology of microspheres (diameter is about 3μm), which are composed of porous nanoflakes. NiO/NF hybrid shows a porous nanoflakes array structure, the thickness of nanoflakes is 10nm. Electrochemical measurements indicate that the maximum specific capacitance of NiO nanopowders is about 85.4 F/g at a scan rate of 5 mV/s, while this value is up to 234.8 F/g for NiO/NF hybrid. Electrochemical impedance spectrum (EIS) data show that the Rs and Rct values of NiO/NF hybrid (1.9Ù and 0.25Ù) are smaller than that of the NiO nanopowders which are coated on nickel foam (3.6Ù and 0.3Ù). In conclusion, the ultrathin porous NiO/NF is directly used as a binderfree supercapacitor electrode, which exhibited significantly improved supercapacitor performance compared to NiO nanopowders.