Nickel precursor-free synthesis of nickel cobalt-based ternary metal oxides for asymmetric supercapacitors

Abstract

Ternary metal oxides based on nickel and cobalt are synthesized on Ni foam as the energy storage electrode using a nickel precursor-free hydrothermal reaction with incorporation of Mo, Fe, Cu, Zn, and Al, aiming to enhance the electrical conductivity and generate more Faradaic reactions via multiple transition states of metals. Ni foam is acted as the current collector and the Ni ion source to reduce precursor cost and enhance contact between electrocapacitive material and substrate. Benefit from the large surface area and vertically growing direction, the nickel cobalt copper oxide electrode shows the highest areal capacitance of 2.28 F cm-2 at 5 mA cm−2 among ternary metal oxide electrodes. An asymmetric supercapacitor based on the nickel cobalt copper oxide positive electrode and an activated carbon negative electrode also shows an areal capacitance of 917 mF cm-2 at 5 mA cm−2, a potential window of 1.5 V, and an areal capacitance retention of 83.2% after 10,000 cycles charge/discharge process. Using the low-cost and effective nickel precursor-free synthesizing method to fabricate novel ternary metal oxides for asymmetric supercapacitors is successfully realized in this work. Further improvements based on this concept is worthy to investigate for achieving more efficient asymmetric supercapacitors for efficient energy storage.