Preparation And Supercapacitive Performance Of Co-based Nanocomposites

As is known to all,the problem of energy and environment become increasingly serious.Therefore,it becomes more and more imminent to develop new energy sources and new types of energy storage devices.Supercapacitor is proven to be the current research hotspot and receive more and more attention from the academic community in the energy field because of its ultra-high power density and energy density.It requires that supercapacitors should have high specific capacitance,high energy density,high power density,and excellent cycle performance,which calls out a big challenge on the selection and preparation of electrode materials.In recent years,transition metal oxides such as cobalt-based oxides(CoO,ZnCo2O4,etc.)which are low-cost,synthesized facilely,and have ultra-high theoretical specific capacities have been much favored.However,the low conductivity,small specific surface area of CoO and the mechanical shedding of ZnCo2O4 materials during chemical reaction limit their application in the field of supercapacitors.In this paper,it is CoO and ZnCo2O4 that we use as the research object.And a Co/CoO core-shell three-dimensional nanoparticle interconnected membrane and a ZnCo2O4/C composite nanowire array material are designed and synthesized via the strategy of compounding metal oxide nanomaterials with conductive materials.Composite nanowire array structure improves the conductivity and specific surface area of the oxide material and obtains a cathode material of a supercapacitor with excellent electrochemical performance.The main research contents and results are as follows:(1)Co/CoO core-shell three-dimensional nanoparticle interconnected membrane are designed and synthesized on a nickel foam current collector.And the effect of CoO shell thickness on the electrochemical performance of Co/CoO core-shell nanomaterials are studied.The Co/CoO core-shell nanomaterials are successfully synthesized via simple process of hydrothermal method,hydrogen annealing and air passivation.The thickness of the CoO shell was adjusted by the means of controlling temperature during air passivation process.XRD,SEM,TEM,and XPS demonstrated the successful synthesis of Co/CoO core-shell nanomaterials.The size of core-shell nanoparticles was not significantly different,whose diameter ranged from 50 to 150 nm.And with increasing the temperature of air passivation(from 50? to 200?),we find that the thickness of the CoO shell increases(from 2.5 nm to 16 nm).Electrochemical performance tests show that the electrochemical performance of the Co/CoO electrode passivated at 150?(Co/CoO-150)is optimal,whose specific capacitance can reach up to 6.08 F/cm2,and the rate performance is favorable.Asymmetric supercapacitors are assembled using Co/CoO-150 as the positive electrode material and activated carbon as the negative electrode.This device had an energy density of 0.51 mWh/cm2 at a power density of 2.03 mW/cm2.Moreover,the device has a very good cycle life.After 10,000 constant current charge and discharge cycles(GCD),the capacitance value remains 85%.(2)ZnCo2O4/C composite nanowire arrays are successfully designed and synthesized on nickel foam.The effects of carbon deposition on sample performance were studied.ZnCo2O4/C composite nanowire arrays are obtained via a simple hydrothermal method combined with low temperature chemical vapor deposition.The structure,morphology and composition of the material were characterized by XRD,Raman,XPS,SEM,and TEM.And the CV,GCD,EIS,and cycle performance of the sample were measured by the electrochemical workstation.The research shows that the deposition of carbon on amorphous ZnCo2O4 nanowire arrays is successfully achieved at lower temperature,which improvs the conductivity of the ZnCo2O4 nanowire arrays.Electrochemical measurements of the electrodes of the two materials show that the electrochemical performance of the ZnCo2O4/C composite nanostructures is better than the pure ZnCo2O4 nanowire array.The specific capacitance of ZnCo2O4/C can reach up to 7.02 F/crm2(2340 F/g)at the current density of 1 mA/cm2,which is almost twice as specific capacitance as pure ZnCo2O4 nanowire array(1190 F/g).Furthermore,ZnCo2O4/C still has good cycle performance at high currents.After 10,000 GCD cycles,its specific capacity retains 92.6%of the initial value.Using ZnCO2O4/C as the positive electrode of the capacitor,activated carbon as the negative electrode,6 M KOH as the electrolyte,and cellulose paper as the separator,the asymmetric supercapacitor device(ZnCo2O4/C//AC)is assembled,when the device is at the power density of 73.17 W/kg,The energy density is 35.75 Wh/kg,In addition,the device was subjected to 10,000 cycles of charge and discharge tests,and it is found that the performance retained about 73.3%after the cycle.In addition,the asymmetrical capacitor ZnCo2O4/C//AC successfully lit the LED bulb,indicating that the ZnCo2O4/C composite nanowire array is a very promising tantalum capacitor material.