Controllable synthesis of nickel doped hierarchical zinc MOF with tunable morphologies for enhanced supercapability

Metal-organic frameworks (MOFs) are attracting tremendous research interest because of their rich redox sites and high specific area which are beneficial for the energy storage applications. Nevertheless, the poor conductivity, low mechanical strength and unsatisfactory capacity severely hinder their wide application. Hence, it is of practical significance to design highly efficient and facile strategy to solve these issues. Herein, vertically oriented ZnO nanorod arrays are applied as precursor to synthesize laminated scale-like and highly-oriented Ni/Zn-MOF/ZnO nanocomposite. Owing to the desirable conductivity resulting from the doping nickel ions and the interaction between ZnO and its relative MOF, the fabricated 0.3Ni/Zn-MOF/ZnO@CC electrode exhibits an electrochemical capacitance of 1693 mF cm^-2 at 1 mA cm^-2. Moreover, the electrochemical capacitance retention of 80.7 % after 2500 cycling numbers is obtained under the constant current density of 10 mA cm^-2 and the low internal resistance R_s of 0.89 Ω is observed. For practical application, the as-synthesized laminated scale-like Ni/Zn-MOF/ZnO@CC nanocomposite is served as positive electrode to fabricate solid-state asymmetric supercapacitor device. Moreover, a 2.5 V indicator could be powered for 8 min when the prepared supercapacitor units are connected. This work demonstrates the promising potential of the synthesized scale-like Ni/Zn-MOF composites for electrochemical energy storage applications.