Ultrathin Porous NiO Nanoflake Arrays on Nickel Foam as Binder-free Electrodes for Supercapacitors

Abstract

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 3 µm), which are composed of porous nanoflakes. NiO/NF hybrid shows a porous nanoflakes array structure, the thickness of nanoflakes is 10 nm. 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 R_s and R_ct values of NiO/NF hybrid (1.9 Ω and 0.25 Ω) are smaller than that of the NiO nanopowders which are coated on nickel foam (3.6 Ω and 0.3 Ω). 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.