Preparation And Electrochemical Properties Of Copper Zinc Compound/Carbon Composite Materials

The demand for efficient energy conversion equipment is growing dramatically since the development of the 21st century.Electrochemical energy conversion devices such as supercapacitors,batteries and electrolytic cells can effectively use and convert the clean energy.Therefore,the research and development of high-performance electrochemical energy conversion device has a significant impact on social development.Electrode material,as an important component,largely determines the application performances of the electrochemical energy conversion devices.How to improve the electrochemical activity of the electrode material becomes the key to preparing high performance electrochemical energy conversion equipment.In general,double-layer supercapacitors mainly based on carbon materials have a good power-density,while redox reaction-based supercapacitors mainly based on transition metal compound（TMC）have a high-energy density.The research on the composite electrode materials based on redox electrode materials and double-layer capacitive electrode materials is of great significance for preparing supercapacitors with both high-power density and energy density.The development of water splitting technology can facilitate the replacement of fossil energy by new energy sources in the future.At present,the noble metal-based electrodes have shown excellent catalytic efficiency,however,the high cost and resource scarcity limit their development prospects.It is of great practical significance to find a cost-controlled catalytic electrode for large-scale commercial application of the water splitting technology.On the other hand,lithium-sulfur battery as a member of battery family has not been applied for mass production because of the poor conductivity of sulfur positive electrode,low utilization rate of active materials and the shuttle effect of lithium polysulfide.Designing sulfur-based host materials with excellent electrical conductivity and enhanced sulfur redox kinetics is an effective way to overcome the problems of low specific capacity and poor chemical stability of lithium-sulfur batteries.Based on the above problems and analysis,this work prepared the flexible electrode of carbonized cotton fabric（Cc）with the abundant natural cotton textile as the precursor material.The self-supporting Cc has the characteristics of light weight,flexibility and the advantages of low cost and easy mass production.Cc was activated by KOH and dyeing technology in order to improve the electrochemical performances.Besides,metal compound heterostructure composite is used to solve the problems of low energy density and slow electrocatalytic kinetics of single carbon material.After confirming the excellent electrochemical performance of the above carbon-based metal compound composite structure,porous activated carbon with high specific surface area was designed based on biomass pine as the host material for lithium sulfur battery（Li-S）sulfur（S₈）cathode.To solve the problem of"shuttle effect"in the process of battery charging and discharging,a multi-metal compound composite system was constructed with the porous activated carbon as the substrate material to improve the conversion efficiency of lithium polysulfide to Li₂S.The metal compound active material cannot only effectively improve the oxidation-reduction ability of the composite electrode but also expose more electrochemical active sites with the help of three-dimensional porous carbon substrate.The specific capacity of the composite electrode has been greatly improved.The main research work of this work is as follows:（1）The carbonized cotton fabric（Cc）was prepared by high-temperature carbonization under the protection of nitrogen using cotton as the precursor.The polysaccharide-structural cellulose composed of glucose monomer transformed into carbon material with electrical conductivity successfully after carbonization.The carbonization temperature has an obvious effect on the molecular structure of Cc.Raman results show that the disorder degree of the carbon atom increases with the carbonization temperature increasing below 800℃,while the degree of disorder was less affected when the carbonization temperature exceeds 800°C.The three-dimensional space structure of the cotton fabric had not collapsed and destroyed after carbonization,but the fiber diameter reduced because of the thermal cracking of the cellulose macromolecule.Cc with the 800℃carbonization temperature as the self-supported electrode showed a capacitance of 97.3 m F cm^-2 at the current density of 2 m A cm^-2.As an OER catalyst,the overpotential of Cc at 10 m A cm^-2 was581 m V.Activated Cc was prepared through KOH and dyeing method to improve the electrochemical performances of the original Cc（p Cc-K and p Cc-D）.The larger specific surface area improves the charge transfer efficiency of the sample in the electrode reaction.The specific capacitance of p Cc-K and p Cc-D reached to 475.3 and 371.8 m F cm^-2 at the current density of 2m A cm^-2;As an OER catalyst,the overpotential of p Cc-K and p Cc-D was 499 and 528 m V at 10m A cm^-2.（2）To solve the problem of the low energy density of single carbon-based materials,a composite electrode composed of porous carbonized cotton,Zn O nanoparticles and Cu S microspheres was prepared by vacuum evaporation technology and solvothermal method.The XRD and Raman results showed that the molecular structure of the Zn O nanoparticles not obviously changed after solvothermal reaction.Zn O nanoparticles accelerate the transfer of charges and ions during the electrode reaction of p Cc-Z（PCc/Zn O composite electrode）.p Cc-Z reached an area specific capacitance/capacity of 518.3/0.14 m F cm^-2/m Ah cm^-2 at the current density of 2 m A cm^-2.The Cu S microsphere introduced by solvothermal method improved the redox property of the composite electrode greatly and further increased the quantity of the transferred charges during the charge-discharge process.p Cc-CZ achieved a high specific capacitance/capacity of 1489.1/0.41 m F cm^-2/m Ah cm^-2.All-solid-state supercapacitor（p Cc ZC-SC）based on p Cc-ZC self-supported electrode and PVA-KOH gel electrolyte achieved a specific capacity of 57.5μAh cm^-2 at the current density of 2 m A cm^-2.The energy density of p Cc ZC-SC was 34.5μwh cm^-2 at the power density of 0.5 m W cm^-2 and maintained 72.4%after 2000 cycles.In addition,p Cc ZC-SC has the characteristics of flexible and lightweight,which shows the excellent application prospects in the field of the functional energy storage.As the catalytic electrode,the rich porous structure of p Cc in p Cc-ZC provides a large electron transfer surface,and the Cu S/Zn O heterostructure improves the ability of the electrode to convert intermediate products during the OER reaction.The overpotential of the p Cc-ZC at 10 m A cm^-2 was 391 m V,and the Tafel slop was 93.2 m V dec^-1.The development of multi-function electrodes not only broadens the application scenario of the products,but also adapt to industrial production.（3）To further optimize the structure of the electrode active materials,p Cc/Cu S/Zn O nanocomposite was prepared by successive ion layer deposition and vacuum evaporation（p Cc-CZ）.The more dispersed Cu S enhanced the utilization of the active sites.The anchoring of Zn O nanoparticles on the p Cc/Cu S surface improved the charge transfer efficiency and the structural stability of the composite system.p Cc substrate could not improve the charge transfer ability of the composite electrode but provide large numbers of reactive sites.Thanks to the synergistic effect of p Cc,Cu S/Zn O particles ternary composites,p Cc-CZ exhibited excellent electrochemical properties.As the supercapacitor electrode,p Cc-CZ has an area specific capacitance/capacity of 2043.1/0.57m F cm^-2/m Ah cm^-2 at the current density of 2 m A cm^-2.The specific capacitance retention of p Cc-CZ after 5000 cycles was 86.3%.The specific capacity and energy density of p Cc CZ-SC reached to 91.4μAh cm^-2 and 54.8μwh cm^-2(0.7 m W cm^-2)at the current density of 2 m A cm^-2,which is better than other supercapacitor devices reported recently.The overpotential of p Cc-CZ at 10 m A cm^-2 was 337 m V,which is comparable to the reported OER performance of the noble metal-based electrocatalysts.（4）Based on the three parts above,biomass-derived pine had been converted into porous carbonized pine（p-Cp）with high specific surface area and charge transfer efficiency by carbonization and KOH activation.Compared with the untreated carbonized pine,p-Cp provided more pore volume to regulate the volume change of S₈ in the redox and increased the reactive sites of the electrode,which effectively improves the utilization of the S₈ active material.The specific discharge capacity of p-Cp at 0.1 C reached to 985.5 m Ah g^-1.The high-value utilization of renewable biomass resources is beneficial to reduce the dependence of battery industry on mineral resources.The shuttle effect of lithium polysulfide during charge-discharge further inhibited by depositing Zn S and Cu S redox medium（p-Cp ZCS）on the surface of p-Cp.The first discharge capacity of lithium-sulfur battery with p-Cp ZCS/S as cathode material reached to 1457.8 m Ah g^-1at 0.1 C,and it remains 885.1 m Ah g^-1 after 50 cycles.Li₂S₆ solution was prepared to test the adsorption performance of the samples.The results show that the adsorption performance for lithium polysulfide of the composite electrode had been obviously improved by the introduction of bimetallic sulfides.Ex-situ XRD was applied to investigate the phase conversion of the battery during the charge-discharge process.The redox activity of the electrode was further enhanced by Cu S.Besides,the in-situ formation of Cu on the electrode surface improved the conductivity of the electrode,which improves the transport efficiency of charge carriers at the electrode-electrolyte interface.