Facile Synthesis Of Supercapacitors Materials By Hydrothermal Route And The Study Of Their Electrochemical Performance

In recent years, owing to increasing concern about the depletionof fossil fuels and environmental pollution, there is an urgent need for clean, efficient, and renewable sources of energy to maintain a sustained, healthy and rapid economic development. As two of the most promising energy storage devices for electric energy storage,lithium-ion batteries?LIBs? and supercapacitors?SCs? have attracted worldwide attention. Especially, supercapacitors have attracted attention owing to their fast recharge ability, high power performance, long cycle life, and low maintenance cost,which allow applications for various power and energy requirements, such as hybrid electric vehicles, short-term power sources for mobile electronic devices, etc. They can complement or even replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. Supercapacitors can be divided into two types, that is, store energy using either ion adsorption?electrochemical double layer capacitors? and fast surface redox reactions?pseudocapacitors?. Generally, pseudocapacitors have higher energy density than the double-layer capacitors. Therefore, most of the current research studies have been focused on pseudocapacitors, and kinds of new capacitive materials including metal oxides, metal sulfides and conductive polymers with high energy density and long cycle life have been developed. In addition, novel materials should have as high specific surface area as possible because the storage capacitance is mainly decided by the surface redox reaction of active materials.The main research contents and results are as follows:?1? The second chapter of the paper, we introduced The synthesis of Zn WO₄ nanowall arrays materials. The microstructures and compositions of these materials were investigated by SEM and TEM, can be known the tablet of a single nanosheet is very thin. All Electrochemical measurements were made in a conventional three-electrodecell containing 3 M KOH aqueous solution as the electrolyte. In current density of 20 m A cm-2 and voltage range of 0-0.65 V for performance of supercapacitor tests, which exhibit areal specific capacitance value of around 2.5 F cm-2, and mass specific capacitance value of 1250 F g-1.?2? The third chapter of the paper, we used one-step hydrothermal method to directly growth Zn Co₂O₄ nanowire cluster nanoarrays materials on nickel foam substrate. Because the reaction time impact the morphology of the materials, westudied the growth process of nanowire arrays. TEM results showed these Zn Co₂O₄ nanowires were actually assembled by very small nanocrystals with the size ranging from 10 to 15 nm. The nanocrystals interconnected with each other and formed a stable nanowire with very small pores. Obviously, these pores could greatly improve the surface-to-volume ratio of the nanowires. The supercapacitor characteristics of the Zn Co₂O₄ nanowire cluster nanoarrays was tested in 3 M KOH aqueous solution. In current density of 20 m A cm-2 and voltage range of 0-0.65 V for performance of supercapacitor tests, which exhibit areal specific capacitance value of around 4.05 F cm-2, and mass specific capacitance value of 1620 F g-1.In different current densities?20 m A cm-2, 30 m A cm-2, 50 m A cm-2, 100 m A cm-2?, 90% of the initial capacitance remained after 6000 cycles, demonstrating excellent cycling stability.?3? The fourth chapter of the paper, to investigate the Zn Co₂O₄ NWCAs for practical application, an asymmetric supercapacitor was made by using an activate dcarbon film on Ni foam as the negative electrodeand Zn Co₂O₄ NWCAs on Ni foam as the positive electrode with one piece of cellulose paper as the separator in 3 M KOH as the electrolyte. The asymmetric supercapacitor was demonstrated excellent electrochemical performance after electrochemical measurements. It exhibited high energy densities of 41.00 and 16.63 W h kg-1at power densities of 384 and 2561 W kg-1,the asymmetric supercapacitors were charged to 3.2 V and a red round LED indicator was lighted.