Morphology variation for the nickel cobalt molybdenum copper oxide with different metal ratios and their application on energy storage

Abstract

Nickel cobalt oxide is widely applied to energy storage devices owing to the high electrical conductivity and abundent redox states. To gain more redox reactions for storaging charges, more metals are incorporated in nickel cobalt oxide to synthesize the multiple metallic oxides. The effects of the synthesizing parameters such as temperature, reaction time, and precursor concentration on the morphology and the electrochemical performance for nickel cobalt based multiple metallic oxides have been intensively discussed in the previous reports. However, the ratio of the metals in the nickel cobalt based multiple metallic oxides is rarely investigated. To more understand the growth and the energy storage ability of the efficient nickel cobalt based multiple metallic oxides, the nickel cobalt molybdenum copper oxide is synthesized on the nickel foam using a facile one-step hydrothermal synthesis in this study for the application on the battery-type electrode for the battery supercapacitor hybrid device. The ratios of the four metals in nickel cobalt molybdenum copper oxide are varied to examine the effect of the metal ratio on the morphology, electrical conductivity, charge transfer resistance and the specific capacitance of the electrodes. The optimized nickel cobalt molybdenum copper oxide electrode shows an areal capacitance of 3.54 F/cm2 corresponding to the capacity of 1.67 mAh/cm2 at 5 mA/cm2, due to the preferable wire-in-sheets morphology and the high electrical conductivity. The battery supercapacitor hybrid device with the optimized nickel cobalt molybdenum copper oxide positive electrode and an activated carbon negative electrode shows an areal capacitance of 0.93 F/cm2 corresponding to the capacity of 0.41 mA h/cm2 at 10 mA/cm2 and a maximum energy density of 13.99 Wh/kg at the power density of 340.42 W/kg. The excellent cycling stability with the areal capacitance retention of 61% after 3600 times repeated charge/discharge process and the Coulombic efficiency of higher than 90% for the entire measurement is also achieved for the battery supercapacitor hybrid device. This study provides careful discussion on the morphology and the electrochemical property relating to the metal ratio for preparing the nickel cobalt molybdenum copper oxide electrode.