Dual-metal ions adjustable nickel and cobalt oxide nanosheets for asymmetric supercapacitors

A series of nickel and cobalt oxide (NCO) nanosheets were synthesized through a two-step hydrothermal-calcined method. Transition metal ions in NCO nanosheets were adjusted by changing the molar ratios of nickel and cobalt ions in precursor solutions. The crystalline phases, morphologies, and structures of the NCO nanosheets were characterized using X-ray diffraction, scanning electron microscope, and X-ray photoelectron spectroscopy. Furthermore, the electrochemical performances of the NCO nanosheets electrodes were tested. The result indicated that the NCO-2 (Ni1.95Co1Ox) nanosheets exhibited high specific capacitance of 1 096.88 F center dot g(-1) under 0.5 A center dot g(-1), which concurrently possessed a cycling ability of 78.26% after 5 000 cycles. Importantly, the asymmetric supercapacitor, which was constructed from the NCO-2 positive electrode and active carbon negative electrode, presented an energy density of 57.70 Wh center dot kg(-1) at a power density of 576 W center dot kg(-1).