A high-performance asymmetric supercapacitor electrode based on a three-dimensional ZnMoO₄/CoO nanohybrid on nickel...

A two-step hydrothermal route was employed to fabricate a ZnMoO₄/CoO nanohybrid supported on Ni foam. The ZnMoO₄/CoO nanohybrid shows a three-dimensional criss-crossed structure. The specific surface area is enhanced from 45 m² g^-1 of ZnMoO₄ to 67 m² g^-1 of the ZnMoO₄/CoO nanohybrid. Furthermore, the existence of electroactive CoO is in favor of reducing the charge transport resistance. The ZnMoO₄/CoO nanohybrid electrode possesses a high capacitance of 4.47 F cm^-2 at 2 mA cm^-2, which is much higher than those of ZnMoO₄ (1.07 F cm^-2) and CoO (2.47 F cm^-2). The ZnMoO₄/CoO nanohybrid electrode also exhibits an ultrahigh cycling stability with 100.5% capacitance retention after 5000 cycles at 20 mA cm^-2. In addition, an asymmetric all-solid-state supercapacitor was assembled using the ZnMoO₄/CoO nanohybrid as the positive electrode and exfoliated graphite carbon paper as the negative electrode. The asymmetric supercapacitor exhibits a superior energy density of 58.6 W h kg^-1 at a power density of 800 W kg^-1 and a considerable cycling stability with 81.8% capacitance retention after 5000 cycles at 5 A g^-1. The ZnMoO₄/CoO nanohybrid demonstrates its tremendous advantages and possibilities as a positive electrode material in energy storage applications. Moreover, for a better understanding of the electrochemical behavior, a combined study of experimental measurements and density functional theory calculations is also applied to illustrate the high-performance of the ZnMoO₄/CoO nanohybrid.