Study On The Synthesis And Supercapacitive Performance Of ZIFs-derived Nanocomposites

Supercapacitors are believed as the promising energy storage device owing to their high power density and long cyclic life.And the electrode material is the critical factor that determines the electrochemical performance of supercapacitors.Zeolitic imidazolate frameworks(ZIFs)are a novel kind of three-dimensional porous materials and owing to their characteristics of high porosity and stability,they can be employed as the template and precursor,especially for the preparation of electrode materials in the energy storage device such as supercapacitors.In this paper,ZIFs-derived carbon materials were prepared and then were employed as the substrate to improve the supercapacitive performance of the electrode material by synthesizing nanocomposites through structural design.The research contents are as follows:(1)Study on the synthesis and supercapacitive performance of ZIFs-derived porous carbon materials:First,Dodecahedral ZIF-67,dodecahedral and hexahedral ZIF-8 were synthesized.Then these ZIFs were heat-treated.N-doped porous carbon with Co particles on its surface was obtained after pyrolyzating dodecahedral ZIF-67.Dodecahedral carbon and hexahedral porous carbon were prepared by pyrolyzing dodecahedral and hexahedral ZIF-8 and they both maintained the structure of precursor.The specific surface area of the hexahedral porous carbon reaches 1142m²/g,and it exhibits the better supercapacitive performance that the specific capacitance is up to 161 F/g at 1 A/g.(2)Study on the synthesis and supercapacitive performance of 3D core-shell MnO₂@C materials:The low-temperature water-bath method was employed.The acicular MnO₂was uniformly anchored on the dodecahedral carbon substrate and then3D core-shell MnO₂@C materials with hollow structure were synthesized.When the water bath time is 6 h,the dispersion of MnO₂on the MnO₂@C composite surface is the best and the core-shell structure is formed.The specific capacitance is 255.5 F/g and capacitance retention can reach 95%after 5000 GCD cycles.Besides,the MnO₂@C//DC asymmetric supercapacitor consisting of MnO₂@C and dodecahedral carbon(DC)electrode materials possesses the energy density of 10.5 Wh/kg at 375W/kg.(3)Study on the synthesis and supercapacitive performance of CoS₂/NC N-doped composites:A two-step heat-treatment method was adopted.Firstly,N-doped porous carbon was obtained by pyrolyzing dodecahedral ZIF-67 under low-temperature.Then Co atoms attached to the surface of N-doped porous carbon were transformed into CoS₂nanoparticles by secondary heat-treatment with sublimated sulfur,hence the CoS₂/NC N-doped composites were synthesized.When the sulfuration time reaches 2h,the specific capacitance of CoS₂/NC-2 composite could reach 1120 F/g,and the rate performance is 78.2%when the current density ranges from 1 to 10 A/g.Besides,capacitance retention reaches 85.2%after 5000 GCD cycles.(4)Study on the synthesis and supercapacitive performance of interconnected sheet-like NiS@C composites:The interconnected sheet-like NiS@C composites were synthesized through the low-temperature water-bath method.The hexahedral porous carbon material plays a supporting role as substrate and NiS nanosheets grow on the hexahedral porous carbon and they interconnect with each other,forming the interconnected nanostructure.When employed as electrode materials,the interconnected sheet-like NiS@C composites present remarkable supercapacitive performance owing to the complex effect that is the combined advantages of double-layer capacitor-type hexahedral porous carbon and pseudocapacitor-type NiS nanosheets.The NiS@C nanocomposites exhibit a high specific capacitance of 1827F/g at 1 A/g and show capacitance retention of 72%at 20 A/g after 5000 GCD cycles.Moreover,the fabricated hybrid supercapacitor NiS@C//HC consisting of NiS@C and hexahedral porous carbon electrode materials has excellent electrochemical performance.It delivers a high energy density of 21.6 Wh/kg at 400 W/kg,and when the power density increases to 8000 W/kg,the energy density could reach 10.8 Wh/kg,along with capacitance retention of 84%after 5000 GCD cycles.This paper contains 46 figures,3 tables,and 118 references.