In-situ construction of metal organic frameworks derived Co/Zn–S sandwiched graphene film as free-standing electrodes for ultra-high energy density supercapacitors

Abstract

Metal organic frameworks (MOFs) with in situ porous nanostructures and high specific surface area have been widely used in supercapacitors, and the reduced graphene oxide (rGO) nanosheets is an excellent electronic conductor and support in loading other materials. Herein, for the first time, we report the unique Co/Zn-MOF derived Co/Zn–S polyhedron homogeneously embedded between the rGO sheets film as a binder-free electrode for high performance hybrid supercapacitor. Using a mild in situ synthesis method and vulcanization process, a 3D nano-electrode material Co/Zn–S@rGO is prepared by combining Zn0.76Co0.24S nanoparticles with rGO film. Among them, Co/Zn–S@rGO-7 samples with optimizing ratio deliver a high capacitance of 1640 F g−1 at the current density of 1 A g−1 in 6 M KOH alkaline aqueous electrolyte. The asymmetric supercapacitor (Co/Zn–S@rGO-7//AC) using Co/Zn–S@rGO as the positive electrode and activated carbon as the negative electrode shows an ultra-high energy density of 91.8 W h kg−1, when the power density is 800 W kg−1. Moreover, the device also shows a high cycle stability under high current density (90.3% capacity retention after 8000 cycles). It shows that the electrode materials prepared by this method has a good application prospect in electrochemical energy storage.