CoMoO\(_4\)-coated Co\(_3\)O\(_4\) hierarchical composite structures grown on nickel foam as ultra-high performance binder-free electrodes

In the realm of supercapacitor energy storage, multi-element transition metal-oxides with high theoretical specific-capacitance values have been extensively explored. However, their poor electrical conductivity and cycling stability limit their applications. In this study, Co-MoO4@Co3O4/NF was formed by loading Co3O4 on the nickel foam (NF) surface as a substrate by solvent co-precipitation method and annealing treatment first, and then growing CoMoO4 on the surface of Co3O4 by hydrothermal reaction and calcination. Co3O4 nanosheets, which are derived from ZIF-67, offer more active sites and simpler ion/electron transport paths. The electrochemical characteristics of the composite electrode can be substantially boosted by the synergistic effect between Co3O4 as the inner layer and CoMoO4 as the outer layer in the CoMoO4@Co3O4/nickel foam hierarchical composite structural materials. When combined with activated carbon (AC) to form an asymmetric supercapacitor, it exhibits a capacitance normalized to unit area of 0.669 F cm2 at 1 mA cm2. Furthermore, the assembled asymmetric supercapacitor demonstrates an energy per unit volume of 209.29 mWh cm−2 at the current flux of 0.75 mW cm−2, and upholds 89% of its Initial surface capacitance after 6000 cycles.