Preparation And Electrochemical Properties Of Cobalt Based Metal Compounds And Their Complexes Derived From ZIF-67

With the rapid development of economy and industry,the traditional fossil energy can no longer meet the energy demand of people.Supercapacitor with its high power density and excellent cycle life has been widely concerned.However,the energy density of supercapacitors is low.In order to prepare supercapacitors with excellent performance,metal organic framework（MOF）ZIF-67 was used as the precursor to prepare Co₃O₄/N-doped carbon composites（Co₃O₄/NC）,CoS/N-doped carbon composites（CoS/NC）and NiCo₂S₄,which were used as the cathode materials of supercapacitors and assembled asymmetrically with activated carbon.The electrochemical performance of supercapacitor was tested.ZIF-67 precursor was prepared by stirring at room temperature method,and Co₃O₄/NC composites with hollow polyhedron structure were successfully prepared by two-step calcination method.The specific capacitance of Co₃O₄/NC composite at 1 Ag^-1 current density is 1144.0 Fg^-1(much higher than 215.0 Fg^-1 of pure Co₃O₄),and the specific capacitance retention rate of Co₃O₄/NC composite is 45.4%at 20 Ag^-1.When the power density of Co₃O₄/NC//AC capacitor is 1037.0 W·kg^-1,the highest energy density is 40.0 Wh kg^-1,and the capacity retention rate is 87.6%after 10000 charge discharge cycles at 5 Ag^-1.Using ZIF-67 as precursor,CoS/NC composites were successfully prepared by one-step chemical vapor deposition（CVD）at three curing temperatures.The results show that the optimal curing temperature is 700℃,and CoS/NC-700 is a hollow polyhedron structure formed by the combination of CoS nanosheets and nitrogen doped carbon skeleton.The specific capacitance is 789.0 Fg^-1 at 1 Ag^-1 current density and 80.2%at 20 Ag^-1 current density.The CoS/NC-700//AC capacitor has the highest energy density of 32.8 Wh kg^-1 when the power density is 620.0 W kg^-1.The capacity retention rate of CoS/NC-700//AC capacitor is 89.2%after 10000 charge discharge cycles at 5 Ag^-1.With ZIF-67 as precursor,NiCo-LDH,NiCo₂S₄ and CoS₂ materials were successfully prepared by introducing nickel source（or without nickel source）into ZIF-67.The results show that NiCo-LDH and NiCo₂S₄ are flower like structures,and CoS₂ is a cage like structure.The specific capacitance of NiCo₂S₄ electrode is 2934.0 Fg^-1 at 1 Ag^-1 current density and 51.1%at 20 Ag^-1 current density.NiCo₂S₄//AC capacitor has the highest energy density of 38.8 Wh kg^-1 when the power density is 993.0 W kg^-1,and the capacity retention rate is 81.2%after10000 charge discharge cycles at 5 Ag^-1.It has excellent cycle performance.