Derivation Of ZIF-67 And Application In Supercapacitors

Currently,the increasing demand on clean and renewable energy advances the development of energy storage systems.Supercapacitor,integrating advantages of traditional capacitor and rechargeable battery,is a type of novel energy storage device with merits such as high energy density,fast charge-discharge rate,and environmental benign.Electrode is one of the most significant factors affecting the performance of supercapacitors.Metal organic framework?MOF?,consisting of metal ions/clusters and organic linkers via coordination bond,is a prominent type of electrode materials owing to its high specific area,tunable composition and structure.Via various derivation approaches,MOF can be converted into diverse functional materials,whose applications have extended into energy storage devices.Among thousands of MOFs,cobalt zeolitic imidazole framework?ZIF-67?is one of the most important presentations owing to its ease synthesis,unique structure and reactive properties.Considering above context,here three types of derivatives were gained via ion exchange technique using ZIF-67 as precursor.The electrochemical performance of these derivatives as supercapacitor electrodes were also investigated.1 Hollow Co₃S₄ derived from ZIF-67 and its electrochemical propertiesUsing Co?NO₃?₂·6H₂O as metal source,2-methylimidazole as organic linker,ZIF-67 with uniform dodecahedron in morphology was firstly synthesized under mild condition.Then,under the hydrothermal conditions,a series of hollow Co₃S₄ was prepared by adjusting the ratio of ZIF-67 and thioacetamide?TAA?,which followed by heat treatment in nitrogen.Subsequently,the effect of this treatment on the structure and performance of Co3S4 was discussed in details.Furthermore,the electrochemical performances of the as-prepared hollow Co₃S₄ were evaluated as electrode of supercapacitor.The results found that the sample gained at 100 mg of TAA dosage?Co₃S₄-100?were superior performance than others.The specific capacitance of Co₃S₄-100 was 668 F/g at 1 A/g.The specific capacitance value retained 86.4 of its initial value after5000 cycles even at 4 A/g.The asymmetric supercapacitor device assembled by Co₃S₄-100 and activated carbon delivers a high energy density of 20.7 Wh/kg at the power density of 716 W/kg.Additionally,the capacity retained 81.4%of the initial value after 2000 cycles.2 Co doped hollow NiO?Co@NiO?derived from ZIF-67 and its electrochemical performanceUsing ion exchange approach,ZIF-67 was directly converted into NiCo layered double hydroxide?LDH?by reacting with Ni?NO₃?₂·6H₂O.After calcine in air atmosphere,NiCo-LDH can further be converted into Co-doped NiO?Co@NiO?hollow dodecahedron.Electrochemical test results showed that the specific capacitance of Co@NiO at 1A/g was as high as 520 F/g.Even if the current density increased by 10 times,the specific capacitance remained at 374 F/g,and the the capacitance decayed to the initial 97.4%after 5000 cycles at 8 A/g.When assembled into an asymmetric capacitor device with activated carbon,the energy density at 749 W/kg was36.2 Wh/kg.After 5000 cycles at 8A/g,the capacitance increased to 105%.3 CoMo-LDH and Mo doped Co_xO_y derived from ZIF-67 for supercapacitor electrodeA series of CoMo-LDH hollow structures were prepared via reacting between ZIF-67 and?NH₄?₆Mo₇O₄ by adjusting the mass ratio of ZIF-67 to?NH₄?₆Mo₇O₄.The time-dependent experiment of CoMo-LDH was carried out to discover the formation mechanism of CoMo-LDH hollow structures.Subsequently,CoMo-LDH hollow structures can be conveniently converted into Mo doped Co_xO_y by calcine treatment in N₂ atmosphere.In addition,the effect of temperature on products structure and performance was discussed in details.Electrochemical measurements revealed that both Mo doped Co_xO_y and CoMo-LDH were suitable for supercapacitor electrodes.Comparatively,electrochemical performance of CoMo-LDH-0.1 is superior in view of specific capacitance?514 F/g at 1A/g?,rate capability?300F/g at 10A/g?,and cycling stability?only lose 16.6%of initial capacitance after 5000 cycles at 4 A/g?.Meanwhile,the assembled CoMo-LDH//AC asymmetric supercapcitor device presented a high energy density of 14 Wh/kg at the power density of 752 Wh/kg and a long cycle stability?76.3%capacitance retention after 2000 cycles?.