Preparation And Capacitive Performance Of Layered Double Hydroxide Composites Deriving From ZIF-67

As we all know,layered double hydroxide?LDH?is a concerned supercapacitor electrode material by virtue of the special two-dimensional layered structure,high specific capacitance and other characteristics.However,the instability of the structure and the poor conductivity limits its application in high rate and long cycle.In this paper,Zeolitic metal organic framework ZIF-67 with high specific surface area is selected to prepare cobalt-nickel layered double hydroxide?Co-Ni LDH?and its composite materials for improving the performance.The dodecahedral ZIF-67 can be translated into cobalt-nickel layered double hydroxide nanocage using acid etching and Kirkhidar effect,combining with the hydrolysis of metal ions.Solvothermal method,reflux method,mechanical stirring method were used to prepare Co-Ni LDH HNCs with hollow nanocage structure.The Co-Ni LDH HNCs prepared by solvothermal method exhibited good capacitance performance.At the current density of 1 A/g,the specific capacity was as high as 1560 F/g and the capacity retention rate was 80% after 5000 cycles at the current density of 8 A/g.In order to improve the dispersion of the electrode materials and increase the actual contact area between electrode materials and electrolyte,CNT@Co-Ni LDH with chain structure and GO@Co-Ni LDH with sandwich structure were prepared by solvothermal method.Compared with original Co-Ni LDH HNCs,the above two electrode materials exhibited better rate capability and cycling stability.At the current density of 10 A/g,the capacity retention rate of GO@Co-Ni LDH and CNT@Co-Ni LDH were 81.1% and 86.1% after 5000 cycle.And at the current density ranging from 2 A/g to 10 A/g,the capacity retention rate of GO@Co-Ni LDH was 80%.Besides,a strategy for constructing rigid chain hierarchical layered double hydroxides deriving from ZIF-67 was designed and proposed.The composite materials of MnO₂@Co-Ni LDH HNCs were prepared using the overlong MnO₂ nanowires at 100 microns as the axis by solvothermal method.The composites exhibited excellent rate capability and cycling stability.At the current density of 1 A/g,the specific capacity was as high as 1436 F/g.And at the current density of 20 A/g,the capacity retention rate was 75.2%.Moreover,the capacity retention rate was 91.1% after 10000 cycles at 10 A/g.It is found that layered double hydroxides deriving from ZIF–67 gives full play to the structural advantage of dodecahedral ZIF-67 and exhibits better performance.Rigid chain hierarchical MnO2@Co-Ni LDH HNCs has a great application potential for supercapacitor materials.