Fabrication And Electrochemical Performance Of WO₃ Supercapacitor Electrode Materials

As an energy storage device,supercapacitors have the advantages of high power density,long cycle life,wide operating temperature limit and being friendly to the environment,therefore,it is widely used in new energy transmission,electric vehicles,electric power transportation,aerospace science and technology,communications,consumer electronics and other fields.The electrode material is an important part of supercapacitor,which plays a decisive role in the performance of supercapacitor.There are three types of electrode materials for supercapacitors:Carbon,Conductive polymer and hydroxide.Tungsten trioxide,a Transition metal oxides material,could be used as an electrode for a pseudo capacitor.WO₃ materials have complex and changeable micro-morphology,can fully contact with electrolyte,provide more active sites and larger specific surface area for charging and discharging process,and have various crystal structures,the invention provides convenience for the ions in the electrolyte to enter and exit the crystal Lattice,and is beneficial to the promotion of the specific capacitance of the super capacitor.Because of the change of valence state of Tungsten Element,there will be oxygen vacancy in WO₃ material.The appearance of oxygen vacancy is beneficial to the charge movement,improves the electrical conductivity of material,and can effectively reduce the internal resistance of material.In this paper,WO₃ materials with different morphologies were prepared by hydrothermal method and electrochemical deposition method,in order to obtain materials with high specific capacitance,high cycle stability,high rate performance and low Equivalent series resistance,the reaction conditions were optimized and the electrochemical properties of WO₃ electrode materials were studied.The specific work of this paper is as follows:（1）WO₃ nanospheres with sea urchin-like three-dimensional structure were prepared by hydrothermal method,and the electrode materials for supercapacitor cathode were prepared by pressing the plates on Stainless Steel Mesh.It is found that the urchin-like WO₃ nanospheres are composed of two-dimensional WO₃ nanorods,which are loosely stacked and linked,and the three-dimensional structure of WO₃nanorods has large specific surface area,the contact area between the material and the electrolyte is increased,the distance of the ion transfer path is reduced,and the reaction site is provided for the redox in the process of pseudo-capacitance energy storage,thus the goal of specific capacitance is achieved.When the current density is0.5 A g^-1,the sample has a high specific capacitance of 488.78 F g^-1.When the current density is increased by 20 times,the ratio of capacitance is 39.1%,and the equivalent series resistance of the sample is 0.966Ωcm^-2,at the same time,it has high cycle stability,after 10000 cycles,the sample still retains 84.75%of the initial capacitance.（2）WO₃ nanospheres with three-dimensional structure were grown directly on the Stainless Steel Mesh Substrate by hydrothermal method.It was found that the Mesh structure of the Stainless Steel Mesh substrate not only provided a certain specific surface area,at the same time,WO₃ nanorods grown on its surface form a three-dimensional network of the first stage,and the WO₃ nanorods self-assembled WO₃ nanospheres are attached to the three-dimensional structure of the first stage,the pores formed by the stacked nanorods with lengths ranging from 20nm to 100nm can be regarded as pores with diameters ranging from 20nm to 100nm.The double three-dimensional structure makes it convenient for ions to enter the crystal lattice and improves the specific capacitance of the electrode material.The results of electrochemical test show that the specific capacitance of the sample is 8.35 F cm^-22 at the current density of 2 mA cm^-2,and the ratio of the sample is 45.5%when the current density is increased by 20 times,when the current density is increased by 50times,the ratio performance is 33.7%,and the initial capacitance is still 93.4%after10000 cycles.（3）WO₃ nanorods were grown on carbon cloth substrate by hydrothermal method,and the samples prepared under different conditions were characterized.It was found that the micro-morphology of WO₃ grown on carbon cloth substrate could be effectively controlled by adjusting the amount of hydrochloric acid,the number and density of WO₃ nanospheres grown on the surface of carbon cloth with different pH precursors are different.When the pH value of the precursor is 1,the grass-like WO₃ nanorods grow on the carbon cloth substrate,and the nanorods with a width of about 20nm and a length of about 1000nm grow oriented outwards on the carbon cloth substrate,the regular morphology provides a very high specific surface area for the electrode material and a reaction site for the reversible redox process.The electrochemical test results show that the specific capacitance is 11.3 F cm^-2 when the current density is 2 mA cm^-2,and the magnification property is 69%when the current density is increased by 20 times,and 55%when the current density is increased by 50times,after 5000 cycles,the capacitance retention of the sample was 80.4%.（4）WO₃ nanoparticles were deposited on carbon cloth substrate by electrodeposition.The diameter of WO₃ nanoparticles grown by electrodeposition was about 25nm and they were piled up on the surface of carbon cloth,completely encased in a carbon cloth skeleton,with no distinctive features to be observed.After electrochemical testing,the WO₃ active material on the carbon cloth substrate is flower-like,which is formed by the reversible contact of Amorphous WO₃ with the electrolyte and redox into a stable crystal structure.The results of electrochemical measurement show that the pseudo-capacitance of the material is not obvious during the charging and discharging process,but the energy storage in the electric double layer is prominent,the specific capacitance of the sample is only 2.35 F cm^-2,and when the current density is increased by 10 times,the specific capacitance of the sample is only 61%.In summary,WO₃ nanospheres with high specific capacitance and good cycle stability were prepared by hydrothermal method under optimized conditions.Different morphology of WO₃ nanomaterials were grown directly on different substrates by hydrothermal method,and the electrode materials of ssm@WO₃ and cc@WO₃ with high specific capacitance and high cycle stability were obtained,the synthesis principle and electrochemical properties of WO₃ were studied.Finally,WO₃was grown on carbon cloth by electrodeposition.WO₃ nanospheres,WO₃@SSM and WO₃@CC integrated supercapacitor cathodes were prepared by hydrothermal method and electrochemical deposition method.Its physical and electrochemical properties were analyzed systematically,and the mechanism was explored.The direct growth of WO₃ on the substrate by hydrothermal method is beneficial to the preparation of high performance electrode materials.Different substrates have certain influence on the electrochemical properties of the samples,such as capacitance and cycle stability,the stable crystal structure of WO₃ is beneficial to the energy storage of the ions in the electrolyte.The complex microstructure composed of nanorods increases the internal resistance of the material but also enhances the specific capacitance of the material.WO₃ material has some potential in the direction of supercapacitor,it is worth further study.