| Supercapacitor is an effective and practical energy storage device.Manganese-based supercapacitors have superior supercapacitor properties and are promising in the field of new energy materials.In this paper,p-phenylenediamine is used as a nitrogen source to dope nitrogen in graphene oxide(GO)to obtain nitrogen-doped modified graphene,which could change the electrochemical activity of the material and improve the conductivity.Furthermore,the ordered Mn O 2nanosheet structure was uniformly grown on the surface of NH2-RGO by hydrothermal method,which reduced the internal resistance of Mn O 2 and avoided the mutual accumulation of graphene sheets as well.Additionly,the Mn element was introduced into the new electrode material ZIF67 by hydrothermal method,and the Mn-ZIF67 electrode material with three-dimensional core-shell structure was obtained.Then the influence of structural composition and element doping on the electrochemical performance of electrode materials was systematically investigated.Using the related laws,Finally,the prepared electrode materials were assembled into asymmetric supercapacitor devices to analysis the effect in practical applications.The main research contents of this paper are as follows:(1)Graphene oxide is first functionalized with p-phenylenediamine and it worked as a substrate for the uniform growth of Mn O2 nanostructure.The?-Mn O2/NRGO composites were synthesized by a simple hydrothermal method.Here,p-phenylenediamine not only serves as a nitrogen source in graphene,but also functions to"anchorize"Mn O2 on graphene.The?-Mn O2/NRGO nanocomposites were characterized by SEM,TEM,XRD,FT-IR and XPS.The electrochemical properties of nanocomposites before and after the addition of NH2-RGO were compared.The test results show that the?-Mn O2/NRGO shows excellent specific capacitance(299.5 F g-1)at the scan rate of 5 m V s-1 and excellent cycle stability(97.8%retention after 8000 cycles)at the current density of 1 A g-1.The improvement is mainly attributed to the specific nanostructure and nitrogen doping.The addition of NH2-RGO provides more active sites for Mn O2 and promotes charge transfer.The synergistic effect of the two materials greatly improves the electrochemical performance of the electrode material.(2)Based on the research of?-Mn O2/NRGO composite electrode material,Mn element was doped by hydrothermal method in a new electrode material ZIF67 with large specific surface area to obtain Mn-ZIF67 electrode material centered on bimetal atom.The morphological structure and properties of the material were characterized by various instruments.The results show that Mn-ZIF67 own a three-dimensional core-shell structure composed of ultra-thin two-dimensional nanosheets and a central skeleton,which exhibits a specific capacitance of 257 F g-1at a current density of 1 A g-1.Moreover,the cyclic performance reached 95.3%of the initial value after 10000cycles.The good performance is attributed to the fact that the doped Mn reduces the internal resistance o f the material itself,and the two-dimensional nanosheet shell on the surface of the material plays an important role in accelerating charge and ion transport.(3)The?-Mn O2/NRGO and Mn-ZIF67 electrode materials were assembled into asymmetric supercapacitor devices,and the value of the two electrode materials in practical applications was studied.The results show that the operating voltage window of the?-Mn O2/NRGO//AC device can be broadened from 0 to 1.8 V,exhibiting good rate performance as well as a good energy density of 24.2 Wh kg-1 at a power density of 242 W kg-1.The voltage window of the Mn-ZIF67//AC device is0-1.4 V,and the energy density is 14.9 Wh kg-1 at a power density of 191.57 W kg-1.Supercapacitor devices based on the two different electrode materials above exhibit large voltage windows and good energy density,which are practical electrode materials. |
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