Preparation And Electrochemical Capacitive Properties Of Nanosized Mn?Fe?Co Oxides

Supercapacitors are applied in a wide range of fields,such as electric hybrid vehicles,digital communication devices and uninterruptible power supplies,due to their high power density,long cycle life,rapid charging-discharging rates,wide range of operating temperatures and environmental friendliness.The performance of supercapacitor is strongly depending on the electrode materials.In order to develop supercapacitors with high energy density,high efficiency and low cost to meet the needs of modern society,tremendous efforts have been focused on constructing unique nanostructured electrode materials for supercapacitors.In this dissertation,nanostructured MnO2/C/TiO2,PPy/MnO2/C/TiO2,RGO/MnO2/C/TiO2,FeOOH/Ag/ZnO and Co(OH)2 electrodes have been prepared for supercapacitor via facile methods.Their microstRuctre and morphology are studied by X-ray diffraction analysis,X-ray photoelectron spectroscopy,fourier transform infrared spectroscopy,Raman microscopy,scanning electron microscopy and transmission electron microscopy.Their electrochemical properties are investigated by cyclic voltammetry,galvanostatic charge/discharge measurement and electrochemical impedance spectroscopy.Firstly,MnO2 was electrochemically deposited on preformed C/TiO2 nanowire arrays to form MnO2/C/TiO2,which directly grown on Ti plate via acetone thermal decomposition.The results suggest that MnO2 nanoflakes have well-distributed covered on the surface of C/TiO2 nanowire arrays,MnO2/C/TiO2 has unique shell/core nanowire arrays structure.The MnO2/C/TiO2 electrode exhibits high specific capacitance of 639 F g-1 at a current density of 1 A g-1 in 0.5 mol L-1 Na2SO4 electrolyte.When the current density increases from 1 to 40 A g-1,the specific capacitance of MnO2/C/TiO2 electrode maintains 93 F g-1.The energy density of the MnO2/C/TiO2 electrode based on the mass of MnO2 reaches 88.8 W h kg-1 at a power density of 0.5 kW kg-1,,and still remains 12.9 W h kg-1 at a power density of 19.8 kW kg-1.The specific capacitance of MnO2/C/TiO2 electrode maintains 320 F g-1 after 1000 galvanostatic charge/discharge cycles at a current density of 2 A g-1,the capacitance retention is 78.7%In order to improve the performance of MnO2/C/TiO2 electrode,PPy and RGO was used to wrap the MnO2 to form PPy/Mno2/C/TiO2 and RGO/MnO2/C/TiO2 electrodes.The electrochemical tests result indicates that PPy and RGO effectively improved the specific capacitance,energy density and cycling stability of MnO2/C/TiO2 electrode.The PPy/MnO2/C/TiO2 electrode demonstrates a high specific capacitance of 715 F g-1 at a current density of 1 A g-1,which is higher 76 F g-1 than that of MnO2/C/TiO2 electrode in 0.5 mol L-1 Na2SO4 electrolyte.The energy density of PPy/MnO2/C/TiO2 electrode can be estimated as 99.3 W h kg-1 at a power density of 500 W kg-1,which is higher 10.5 W h kg-1 than that of MnO2/C/TiO2 electrode.After 1000 galvanostatic charge/discharge cycles at a current density of 10 A g-1,the specific capacitance of PPy/MnO2/C/TiO2 and MnO2/C/TiO2 electrode is 210 F g-1 and 152 F g-1,and the capacitance retention is 84.0%and 80.9%,respectively.In addition,the RGO/MnO2/C/TiO2 electrode has a high specific capacitance of 822 F g-1 at a current density of 1 A g-1,which is higher 183 F g-1 than that of MnO2/C/TiO2 electrode in 0.5 mol L-1 Na2SO4 electrolyte.The energy density of RGO/MnO2/C/TiO2 electrode can be estimated as 114.2 W h kg-1 at a power density of 500 W kg-1,which is higher 25.4 W h kg-1 than that of MnO2/C/TiO2 electrode.After 5000 galvanostatic charge/discharge cycles at a current density of 10 A g-1,the specific capacitance of RGO/MnO2/C/TiO2 and MnO2/C/TiO2 electrode is 246 F g-1 and 150 F g-1,and the capacitance retention is 87.4%and 79.8%,respectively.Then,ZnO nanorods were grown on Ni foam via a simple and convenient wet chemical process,and FeOOH was electro-deposited on Ag decorated ZnO nanorods to form FeOOH/Ag/ZnO.The results suggest that Ag particles homogeneous distributed on ZnO nanorod can effectively enhance the electrochemical performance of the as-prepared electrode through improving its electrical conductivity.The FeOOH/Ag/ZnO electrode exhibits high specific capacitance of 376.6 F g-1 at a current density of 1 A g-1 in 0.5 mol L-1 Li2SO4 electrolyte.When the current density increases from 1 to 10 A g-1,the specific capacitance of FeOOH/Ag/ZnO electrode maintains 126.1 F g-1.The energy density of the FeOOH/Ag/ZnO electrode reaches 33.5 W h kg-1 at a power density of 400 W kg-1,and still remains 11.2 W h kg-1 at a power density of 4000 W kg-1.The specific capacitance of FeOOH/Ag/ZnO electrod maintains about 127 F g-1 after 1000 galvanostatic charge/discharge cycles at a current density of 6 A g-1,the capacitance retention is 70.3%.Finally,Co(OH)2 buds direct growth on Ni foam(Co(OH)2/Ni foam)is prepared via a hydrothermal method.These Co(OH)2 buds are made up by several Co(OH)2 rods,which consist of several nanolamellas.The BET specific surface area of Co(OH)2 sample is 88.9 m2g-1,and pore size is about 1?5 nm.The Co(OH)2/Ni foam electrode exhibits high specific capacitance of 2041 F g-1(6.12 F cm-2)at a current density of 3 mA cm-2(1 A g-1)in 6 mol L-1 KOH electrolyte.When the current density increases to 60 mA cm-2(20 A g-1),the specific capacitance of Co(OH)2/Ni foam electrode maintains a high level of 811 F g-1(2.43 F cm-2).The specific capacitance of Co(OH)2/Ni foam electrode maintains 1080 F g-1 after 1000 galvanostatic charge/discharge cycles at a current density of 18 1A cm-2(6 A g-1),the capacitance retention is 72.4%.Moreover,an asymmetric supercapacitor was successfully assembled,in which Co(OH)2 buds/Ni foam and AC used as positive and negative electrode,respectively.The Co(OH)2//AC asymmetric supercapacitor exhibits high specific capacitance of 59.2 F g-1(1.151 F cm-2)at a current density of 3 mA cm-2.When the current density increases to 60 mA cm-2,the specific capacitance of Co(OH)2//AC asymmetric supercapacitor maintains 20.8 F g-1(0.53 F cm-2).The energy density of the Co(OH)2//AC asymmetric supercapacitor reaches 20.3 W h kg-1 at a power density of 90.6 W kg-1,and still remains 2.8 W h kg-1 at a power density of 719.5 W kg-1.The specific capacitance of Co(OH)2//AC asymmetric supercapacitor maintains 30.9 F g-1 after 1000 galvanostatic charge/discharge cycles at a current density of 18 mA cm-2,the capacitance retention is 69.3%.