Construction of NiCo ₂ O ₄ nanosheet-decorated leaf-like Co ₃ O ₄ nanoarrays from metal–organic framework for high-performance hybrid supercapacitors

A rational design of heterostructures for electrode materials is highly desired for boosting the electrochemical performance, but it is still challenging, especially through a cost-effective method. Herein, novel NiCo2O4 nanosheet-decorated leaf-like Co3O4 nanoarrays have been constructed on a Ni foam using a leaf-like Co-based metal-organic framework (Co-MOF-L) template, which can be simply prepared in an aqueous solution at room temperature. Combining the merits of MOF derivatives and the free-standing core-shell heterostructure, the leaf-like Co3O4@NiCo2O4 nanoarray electrode displayed a high specific capacity of 544.2 C g-1 at 1 A g-1, which is almost 9.3 times that of Co3O4 (58.3 C g-1) and 6 times that of NiCo2O4 (92.1 C g-1). It also displayed a good rate capacity (65.5% at 10 A g-1) and superior long-term stability (93.0% capacity retention over 5000 cycles at 10 A g-1). Moreover, a hybrid supercapacitor (HSC) assembled from the battery-type Co3O4@NiCo2O4 electrode and a capacitive activated carbon (AC) electrode delivered a high energy density of 36 W h kg-1 at a high power density of 852 W kg-1 with good cycling stability, demonstrating a capacity retention of 89.5% after 10 000 cycles at 10 A g-1. Furthermore, two connected HSCs could light up a red light-emitting diode (LED). Therefore, the as-fabricated leaf-like Co3O4@NiCo2O4 nanoarrays hold great promise as binder-free electrodes in electrochemical energy storage devices.