Advanced binder-free electrodes based on CoMn₂O₄@Co₃O₄ core/shell nanostructures for high-performance supercapacitors

Three-dimensional (3D) hierarchical CoMn₂O₄@Co₃O₄ core/shell nanoneedle/nanosheet arrays for high-performance supercapacitors were designed and synthesized on Ni foam by a two-step hydrothermal route. The hybrid nanostructure exhibits much more excellent capacitive behavior compared with either the pristine CoMn₂O₄ nanoneedle arrays alone or Co₃O₄ nanosheets alone. The formation of an interconnected pore hybrid system is quite beneficial for the facile electrolyte penetration and fast electron transport. The CoMn₂O₄@Co₃O₄ electrode can achieve a high specific capacitance of 1627 F g^-1 at 1 A g^-1 and 1376 F g^-1 at 10 A g^-1. In addition, an asymmetric supercapacitor (ASC) was assembled by using the CoMn₂O₄@Co₃O₄ core/shell hybrid nanostructure arrays on Ni foam as a positive electrode and activated carbon as a negative electrode in an aqueous 3 M KOH electrolyte. A specific capacitance of 125.8 F g^-1 at 1 A g^-1 (89.2% retention after 5000 charge/discharge cycles at a current density of 2 A g^-1) and a high energy density of 44.8 W h kg^-1 was obtained. The results indicate that the obtained unique integrated CoMn₂O₄@Co₃O₄ nanoarchitecture may show great promise as ASC electrodes for potential applications in energy storage.