Preparation And Electrochemical Properties Of Carbon-based Composites Loaded With Manganese Ferrite Quantum Dots

Supercapacitors are new environment-friendly energy storage devices between traditional capacitors and batteries.They take the advantages of high power density,fast charge/discharge,long cycle life and good safety.However,due to the limitation of energy storage mechanism,they have low energy density.According to E=1/2CV²,optimizing the structural design of electrode materials and improving the specific capacity C are effective ways to build supercapacitors with high energy density.Therefore,reducing the size of electrode materials to the quantum level and combining carbon materials with transition metal compounds or conductive polymer are effective methods to improve the performance of supercapacitors.Carbon materials with large specific can be used as conductive carbon substrate to support the metallic compounds.Besides,MnFe₂O₄ has high specific capacity and the quantum-sized MnFe₂O₄ has more rich active sites,which can improve the reaction rate and electron transfer kinetics.This paper mainly focuses on the preparation and electrochemical properties.of carbon substrate supported MnFe₂O₄NDs composite electrode materials The results in this paper are as follows:（1）First of all,we used natural flake graphite as the raw material to prepare the graphite oxide（GO）as conductive carbon substrate,and then prepared MnFe₂O₄NDs@GO composites with Fe（CO）₅ and Mn₂（CO）₁₀ as precursors by one-step solvothermal method.The composites show excellent electrochemical properties in KOH electrolyte.Among them,when the voltage window is-1.0-0.2 V,the MnFe₂O₄NDs@GO-400 composite delivers a high specific capacity of 303 F/g.When the voltage window is widened into-1.1-0.3 V,the specific capacity can reach439 F/g.The capacity retention rate of the supercapacitor constructed by the composites is 20.4%after 10000 cycles at the current density of 1 A/g.（2）Furthermore,we coated MnFe₂O₄NDs with carbon by secondary solvothermal method.Carbon coating MnFe₂O₄NDs@C/GO-400 delivers a high specific capacity of 302 F/g at 1 A/g.When the voltage window is widened into-1.1-0.3 V,the specific capacity can reach 339 F/g in aqueous electrolyte.Besides,the constructed supercapacitor also shows excellent capacity retention（about 75.3%）after 10000 cycles at the current density of 1 A/g.（3）Addtionally,we prepared 3DFC with the sodium citrate as raw material and then prepared MnFe₂O₄NDs@3DFC composites with Fe（CO）₅ and Mn₂（CO）₁₀ as precursors by one-step solvothermal method.In 2 M KOH electrolyte,the specific capacity of MnFe₂O₄NDs@3DFC can reach 58 F/g at the current density of 1 A/g,which is nearly 71%higher than that of 3DFC.At the same time,the capacity retention rate of MnFe₂O₄NDs@3DFC composites is 53.9%after 10000 cycles at the current density of 1 A/g.In addition,the specific capacity of 3DFAC-700,which is the best activation product of 3DFC,can reach 165 F/g in KOH electrolyte.Besides,the specific capacity of MnFe₂O₄NDs@3DFAC composites can reach 408 F/g.In addition,due to the high viscosity of EMIMBF₄ ionic liquid,the ionic conductivity is lower than that of the aqueous electrolyte.Besides,the energy storage mechanisms of two kinds of electrolytes are different.Therefore,at the same current density,the above composites show lower specific capacity in EMIMBF₄ ionic liquid.