| As an advanced energy storage device,supercapacitors play an important role in the development and utilization of clean energy.In order to meet the requirements of practical applications,the electrochemical properties of supercapacitors should be further improved.The performance of electrode materials can be optimized in terms of composition and structure.As for composition,transition metal oxides and sulfides have been commonly used as electrode materials,but single-component materials still have problems such as low specific capacitance and poor cycling stability.Therefore,preparing composite materials is an important strategy to improve the performance of electrode materials.Based on this,how to design the structure of composite material so that different components can give full play to their respective advantages and make up for defects,so as to maximize the synergistic effect,and obtain a composite electrode material with better performance has become an urgent problem.In this paper,by elaborate design of the composition and structure,we prepared composite electrode material with transition metal oxide and sulfide through simple synthesis method,which exhibited excellent electrochemical properties.The main contents are as follows:(1)Using Co(NO3)2·6H2O,Fe(NO3)3·9H2O,urea and NH4F as raw materials,CoFe2O4/CoFe2S4 composite nanosheets were grown on a nickel foam substrate by simple hydrothermal synthesis and sulfurization method.Experimental results proved that when the degree of S2-was 10 mM,the CoFe2O4/CoFe2S4 composite material showed the best electrochemical performance,and the specific capacitance was 4.6 F/cm2.In addition,using CoFe2O4/CoFe2S4 material and activated carbon as the positive and negative electrodes,respectively,the asymmetric supercapacitor was assembled and achieved the maximum energy density of 19.8 Wh/kg and power density of 1250 W/kg,as well as excellent cycling stability.The outstanding electrochemical performance can be attributed to the synergistic effect of the CoFe2O4 and CoFe2S4 components,as well as large specific surface area and smooth ion diffusion pathway of the nanosheet structure.(2)The core-shell NiMoO4 nanorod@NiMoS4 nanosheet composite material was controllably prepared by hydrothermal synthesis and in-situ sulfidation method.When the concentration of S2-was 10 mM during sulfidation process,the size of the prepared NiMoO4@NiMoS4 nanorod was about 100 nm and the length was about 1 ?m,with the NiMoS4 nanosheets uniformly distributed on the outer layer of the NiMoO4 nanorods.The specific capacitance of the composite material was 832.3 F/g,and the asymmetric supercapacitor assembled using the material as positive electrode and reduced graphene oxide as negative electrode exhibited the maximum energy density of 22.84 Wh/kg and power density of 3750 W/kg as well as excellent cycling stability.This result shows that the electrochemical performance improvement of the material is due to well-designed composition and structure:First,sulfides improve the electron conductivity.Second,the core-shell nanosheet-coated-nanorod structure increases the specific surface area and builds smooth electron transportation pathway.(3)Cu2-xS@CoS2 core-shell nanowire arrays were successfully grown on the surface of copper foam by anode oxidation,chemical bath growth,and hydrothermal sulfidation method.The Cu2-xS@CoS2 core-shell nanowires have a conical porous structure with size between 100-300 ?m.Electrochemical tests showed that the highest specific capacitance can reach up to 1007 F/g,and the capacity after 5000 charge-discharge cycles can still retain 113.6%of the initial capacity.Besides,the assembled asymmetric supercapacitor using the material and reduced graphene oxide as electrodes also exhibits high energy density(E=35.4 Wh/kg)and power density(P=8250 W/kg)as well as excellent cycling stability(capacity remains 104.7%after 8000 cycles).The result indicates that the composite is a very promising electrode material for supercapacitor. |
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