Research On The Preparation And Performance Of Iron-Based MOF Derivatives And Their Composites For Supercapacitor

The rapid expansion of the global economy is driving an increase in demand for the development of clean energy storage devices.Supercapacitors are considered a promising class of energy storage devices due to their high power density,fast charging and discharging rates,and long cycle life.In this study,a self-template etching and co-precipitation simultaneous reduction strategy was adopted.In the synthetic process,urea was introduced as the precipitant and reducing agent.By using metal ion etching and co-precipitation,MIL-88A（Material of Institute Lavoisier-88A）and MIL-88A/GO were converted into Iron Cobalt Nickel Carbonate Hydroxides（FeCoNi-CH）composites while retaining their original morphology,and graphite oxide（GO）was partially reduced to partially reduced graphite oxide（p-r GO）with strong conductivity at the same time.The FeCoNi-CH/p-r GO was prepared successfully.The electrochemical properties of the composites were optimized by adjusting the preparation conditions.Finally,FeCoNi-CH/p-r GO with the best performance was used as the cathode,and it was assembled into different Hybrid Supercapacitors（HSCs）with different anode materials（Activated Carbon（AC）,Fe OOH and Fe OOH/AC）to compare and investigate the effect of different anode materials on the electrochemical performance of HSCs and further explore their practical application capability.（1）Self-template MIL-88A was successfully prepared by the hydrothermal method and converted into FeCoNi-CH by self-template etching and co-precipitation,and the effects of the Co/Ni ratios as well as etching and co-precipitation times on the crystal structure and electrochemical properties of the resulting materials were investigated.The crystal structure of FeCoNi-CH obtained under different preparation conditions differed,which in turn affected the electrochemical properties of the materials.The material（FeCoNi-CH-10）has the best electrochemical performance when the dosing ratio of cobalt and nickel salts is 1:1（Co/Ni=1:1）and the etching and co-precipitation time is 10 h.The specific capacitance is calculated to reach1110 F·g^-1at 0.5 A·g^-1.The rate performance and cycling performance are not satisfactory,and the specific capacitance is only 356 F·g^-1at 10 A·g^-1（32.1%）.After 1000 charge/discharge cycles at 5 A·g^-1,the specific capacitance remains at 55.6%of the original one.（2）The hydrothermal method was used to successfully prepare self-template MIL-88A/GO,and the same method was used to prepare FeCoNi-CH/p-r GO under the optimal conditions discussed above,and the effect of GO content on the electrochemical properties of the resulting materials was investigated.The material（FeCoNi-CH/p-r GO-0.5）has the best electrochemical performance when the GO content is 0.5 wt%.The specific capacitance reaches 1346 F·g^-1at 0.5A·g^-1.The rate performance and cycling performance are improved,and the specific capacitance is 747 F·g^-1at 10 A·g^-1（55.5%）.Notably,the specific capacitance can be maintained at 427 F·g^-1even with 20 A·g^-1.After 1000 charge/discharge cycles at the same current density of 5 A·g^-1,the capacitance remains at 61.5%of the original capacitance.（3）The electrochemical properties of FeCoNi-CH-10 and FeCoNi-CH/p-r GO-0.5 were systematically compared,and the charge storage mechanism as well as the reason for the enhanced electrochemical performance were revealed.The charge storage mechanism of FeCoNi-CH-10 and FeCoNi-CH/p-r GO-0.5 electrode materials is dominated by the diffusion-controlled battery-like behavior according to reaction kinetic theory.Furthermore,the comparison results of specific capacitance,rate performance,cycle performance,and electrochemical impedance show that the electrochemical performance of the electrode material is improved after composing p-r GO,which is primarily attributed to the improved conductivity of electrode materials.（4）The FeCoNi-CH/p-r GO-0.5 and Fe OOH/AC(m _{Fe OOH}:m _AC=1:2)were used as the cathode and anode,respectively,to assemble the FeCoNi-CH/p-r GO//Fe OOH/AC HSC and the optimal potential window was 0～1.6 V.The specific capacitance is 132 F·g^-1at 0.5 A·g^-1and is maintained at 40 F·g^-1at 10 A·g^-1.The specific capacitance is maintained at 66.5%of the original capacitance after 3000 charge/discharge cycles at 5 A·g^-1.The energy density of FeCoNi-CH/p-r GO//Fe OOH/AC HSC at a power density of 400 W·kg^-1is 46.93 Wh·kg^-1,and even at a high power density of 8000 W·kg^-1,an energy density of 14.3 Wh·kg^-1can still be maintained.A comparison of the electrochemical performance of different HSCs assembled with different anode materials（AC,Fe OOH and Fe OOH/AC）was also made.