Preparations And Supercapacitive Performances Of RuO₂?MnO₂ And Alizarin /ZIF-8 Derived Carbon Material Composites

Because the supercapacitor bears the advantages of high power density,long cycle stability and wide temperature range,it has been applied in many fields.However,the relatively low energy density still cannot satisfy the energy storage which has higher requirements for energy density.At present,many researchers focus on improving energy density of supercapacitors.From the calculation formula?E =0.5 CV2?,it can be seen that the energy density of the capacitor could be improved by broadening the cell voltage of device and increasing the specific capacitance.As well-known,the specific surface area and pore size distribution of the electrode material are important factors that affect specific capacitance.Therefore,the design and synthesis of electrode material with large specific area and appropriate pore size parameters are particularly important for improving the electrochemical performance of supercapacitors.In recent years,the Metal-organic frameworks have attracted much attention in many research fields due to its high specific surface area,high porosity and adjustable pore diameter.As a kind of porous material,the open pore structure of MOFs is an innate advantage,which can provide the channel for ion transmission during the electrochemical process,thus,it is also regarded as one of the ideal templates for synthesis of porous carbon materials.Given this,we choose MOFs as sacrificial template to prepare porous carbon?PCs?.As a result,we achieved nanocomposites,in which the PCs used as a conductive substrate to grow metal oxides or modified with electrochemical redox active organic molecules noncovalently.Furthermore,the resultant composites are characterized by physical and chemical analysis.Finally,the assembly of asymmetric/symmetric supercapacitors is carried out to evaluate the practical energy storage performance of the materials.The main contents are shown as follows:?1?In this study,we employed traditional method to synthesize zeolitic imidazolate framework-8 crystals?ZIF-8?,one of the well-known metal organic frameworks?MOFs?with zeolite-like pore structure.Then,ZIF-8 crystal was served as a sacrificial template and carbon resource to prepare nanoporous carbons material?PCs?with high specific surface area?1230 m2 g-1?and abundant pore structure?average pore diameter is 2.8 nm?.Finally,we used conventional reflux andsubsequent thermal treatment to achieve composites,in which the PCs exploited as a substrate to grow ruthenium oxide?Ru O2?nanoparticles on its surface.The resulting Ru O2/PCs composite with 70.7 wt % Ru O2 loading revealed excellent electrochemical performances in terms of high specific capacitance?539.6 F g-1 at 1 A g-1?and good rate capability?capacitance retain 81.5 % at 200 A g-1as compared to that of 1 A g-1?in three electrode system.Furthermore,the symmetric supercapacitor based on Ru O2/PCs electrodes delivered a high energy density of 23.38 Wh kg-1 at a power density of 600 W kg-1,indicating a potential application prospect.?2?The nanoporous carbon material?PCs?with merits of high specific surface area,high porosity and polyhedral morphology was obtained from carbonizing the ZIF-8 crystal directly.Then the PCs was served as substrate and reductant to react with KMn O4 under room temperature and weak acidity simultaneously,resulting in that a three-dimensional lamellar MnO₂ grown on the surface of PCs.The micro-structure of the resulting MnO₂/PCs composite is conducive to the storage and rapid transfer of electrolyte during the electrochemical process.In three-electrode configuration,the MnO₂/PCs achieve a specific capacitance of 199 F g-1 at current density of 1 A g-1in 1 mol L-1Na2SO4 electrolyte.In order to evaluate the practical application of the prepared MnO₂/PCs composite material,an asymmetric supercapacitor?ASC?is assembled by using the MnO₂/PCs as positive electrode and PCs as the negative electrode.The as-assembled asymmetric device presents an energy density of 10.5 Wh kg-1 along with power density of 950 W kg-1 under a cell voltage of 1.9 V.?3?Organic molecules with electrochemical activity have been demonstrated to possess advantages and potential in energy storage in recent years.The anthraquinone derivative Alizarin?AZ,1,2-dihydroxy-9,10-anthracenedione?was selected to functionalize PCs through non-covalent functionalization.In three-electrode configuration,due to the electrochemical activity of two organic functional groups?hydroxyl and carbonyl?in AZ,the AZ/PCs electrode shows two pairs of reversible peaks in positive and negative potential regions during the cyclic voltammetry process.The resultant AZ/PCs composites delivers high specific capacitance of 391.8 F g-1 at the specific current of 1 A g-1,which is high than that of PCs.Furthermore,thesymmetric supercapacitor?SSC?exhibited high energy density of 13.2 Wh kg-1 along with power density of 700 W kg-1in aqueous electrolyte.