Application Of Metal Organic Frameworks And Their Derivatives In Supercapacitor

With the over-exploitation of traditional energy sources,people are paying more and more attention to energy issues.The use of most renewable energy has regional and timeliness limitations,which urgently requires people to deepen the research on energy storage devices.As a common energy storage device,supercapacitors have the advantages of high power density,fast charging and discharging speed,and high safety.However,the low energy density of supercapacitors relative to conventional secondary batteries is the main reason hindering their development.The properties of electrode materials largely determine the performance of supercapacitors,so exploring suitable electrode materials is the key to improving the performance of supercapacitors.In this paper,we take porous MOFs(Metal organic frameworks)as the starting point,and through different utilization of it,we have prepared MOF/Cu2+1O composites and LDH(Layered double hydroxide)core-shell homogeneous structures,and explored their supercapacitor performance.The work content is as follows:(1)In order to prevent the pollution caused by the use of organic reagents in the hydrothermal synthesis of MOF materials,and to improve the poor conductivity of the original MOF materials when applied to electrode materials,we used the in-situ oxidation method to grow uniform rod-shaped copper hydroxide on the surface of the copper foam.,and then a variety of Cu2+1O/Cu-MOF cluster structures were prepared by vapor deposition.The sample obtained after 1 hour of reaction has the best morphology and performance.When it is used as a cathode material for asymmetric supercapacitors,the specific capacity can reach 2.498 F cm-2 at a current density of 2m A cm-2.After 10,000 cycles of testing at high current density,83% of the initial capacity can still be maintained.Furthermore,the asymmetric supercapacitor assembled with Cu2+1O/Cu-MOF as the cathode and activated carbon as the anode provides a high energy density of 38.3 Wh kg-1 at a power density of 824.6 W kg-1.The good properties and simple and safe preparation make Cu2+1O/Cu-MOF a promising electrode material for supercapacitors.(2)The actual capacity of nickel-cobalt LDH is much lower than the theoretical value,and it is easy to stack during the reaction.In order to solve the above problems,we used nickel foam as the base,covered the rod-shaped nickel-cobalt LDH on the foamed nickel by hydrothermal reaction and used it as the precursor,and constructed the core-shell homogeneous structure of nickel-cobalt LDH by in-situ transformation and etching of MOF.By controlling the growth time of MOFs,we obtained materials with different morphologies and properties,and the MOFs grown for 5 h had the best morphology and properties after being etched.At a current density of 1 A g-1,a capacity of 2540.2 F g-1 can be provided,and the assembled asymmetric supercapacitor still retains 90.85% of the capacity after 5000 cycles,and exhibits a power of 751.1 W kg-1Density and energy density of 19.93 W kg-1,three of these devices can be connected in series to light up LED light bulbs.The core-shell structure constructed by this method effectively avoids the core-shell phase separation that occurs in the common hydrothermally prepared core-shell structure,and reduces the internal resistance.The core-shell is composed of nickel-cobalt LDH with a large theoretical capacity,and the synergistic effect between the core and the shell greatly increases the capacity of the material.