High performance energy storage electrodes based on 3D Z-CoO/RGO nanostructures for supercapacitor applications

Highlights: • The Z-CoO/RGO has been firstly fabricated through a in situ hydrothermal method. • The Z-CoO/RGO obtained outstanding mass specific capacity and high conductivity. • The device with Z-CoO/RGO shows ultra-low resistance and stable storage performance. In this paper, by precisely tuning the structure of composite, a 3D silkworm cocoon-like composite material based on reduced graphene oxide (RGO) and Z-CoO (with a ZIF-67 as precursor) are prepared through a in situ hydrothermal method. This Z-CoO/RGO nanocomposite exhibits a highly opened nanostructure and high conductive capability. The electrochemical performance reveals that an outstanding mass specific capacity (275 F g⁻¹ at current density of 1 A g⁻¹), which is much higher than the pure ZIF-67 with 2.7 F g⁻¹, and excellent resistance characteristic are obtained due to the excellent synergistic effect between the MOFs and RGO. Moreover, a hybridized asymmetric supercapacitor with Z-CoO/RGO as anode and active carbon as cathode is constructed. The device shows ultra-low resistance (the equivalent-series resistance and the charge-transfer resistance are 1.13 Ω and 0.43 Ω, respectively) and stable cycle life about 1000 times is observed. This Z-CoO/RGO electrode also presents high current loading performance for possible high-power density type devices. Our work reveals that the straightforward hydrothermal treatment is a promising method for the preparation of dedicated MOFs complex nanostructure for high performance supercapacitor electrode applications.