Preparation And Electrochemical Capacitance Properties Of Manganese Oxide And Ruthenium Oxide Composites

With the ever increasing consumer electronic products and the fast developing of electric vehicle,efficient electrical energy storage?EES?devices are urgently needed.Supercapacitor is considered as a preferable candidate energy storage device for electronics and electric vehicles application due to its high power density,long cyclic stability and rapid charge/discharge rate.However,compared with batteries,the relative low energy density greatly limits its development and application.To overcome such issue,in this dissertation,the ruthenium dioxide and/or manganese dioxide were composited with different type carbon materials?graphene,CNT and activated carbon?by using different production methods.Based on these materials,asymmetric supercapacitors with high energy density are finally constructed by designing of nanostructure electrode materials with high specific capacitance or increasing the operating voltage of supercapacitors.The microstructure and morphologies were investigated by X-ray diffraction spectroscopy?XRD?,Raman,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and so on.In addition,the electrochemical performances of the as-prepared materials and asymmetric supercapacitors have been examined by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectra.The main work is the following:The composite of manganese dioxide and biomass-derived activated carbons has been successfully synthesized by two-step processes,including a molten salt synthesis of porous activated carbons?PACs?and in situ hydrothermal deposition of MnO₂.Up on the carbonization process,wheat bran is used as low-cost precursor and a mixture of NaCl/ZnCl2acts as combined solvent-porogen.The resultant PACs display a hierarchical porous structure with micro-,meso-and macro-porous and large specific surface area up to 1058 m² g^-1 and as well as high specific capacitance of 288 F g^-1 with excellent cycle performance?98.4%retention over 10,000 cycles?in three-electrode system using 6 mol L^-1 KOH electrolyte.Furthermore,the PACs-50@MnO₂//PACs-50 asymmetric supercapacitor exhibites a high energy density of 32.6 Wh kg^-1 with 93.6%capacity retention at over 10,000 charge/discharge cycles in 0.5 mol L^-1 Na₂SO₄ aqueous solution.TiC@C core-shell array direct grown on Ti6Al4V substrate is prepared through a facile chemical vapor deposition method.And then,freestanding one-dimensional MnO₂ nanoflakes are successful prepared through a simple hydrothermal reaction by using the carbon shell of TiC@C core-shell arrays as the sacrificial template and conductive skeleton.Finally,the thickness of the carbon shell decreased but also remained and the ultrathin MnO₂ nanoflakes with thickness less than 5 nm uniformly grow on the surfaces of the TiC@C nanowire to form a core-double shell structure after the hydrothermal reaction.The as-prepared 2D electrode shows a high specific capacitance of 598.8 F g^-1 and 85.8%of its initial capacitance is retained after 10,000 cycles at a high discharge current density of 10 A g^-1.On the basis of the above experiment,TiC@C-MnO₂ is modified by graphene.Ultra-thin 2D graphene nanosheet decorated on the surface of 1D TiC@C nanowire array is prepared by one-step optimized electrodeposition.And then,the prepared TiC@C-graphene nanosheet nanowire array is used as the support to immobilize MnO₂ nanoflakes via one-step hydrothermal method.The as-prepared 3D TiC@C-rGO-MnO₂ electrode obtained high specific capacitance(856 F g^-1 at the current density of 2 A g^-1),good rate capability(69.1%capacitance retention at 40 A g^-1 vs.2 A g^-1),superior cycling stability(85.7%capacitance retention after 10,000 cycles at 10 A g^-1).By using safranin?SAF?as a codispersant,GNS and MWNT were first uniformly dispersed in water and then deposited on Ni foam via a facile“dip&dry”method?denote as GM-Ni?.Then,the 3D GM-Ni electrode as substrate,the incorporation of Mn O2 nanoflakes between graphene and CNT are achieved by an in situ chemical reaction with KMnO4?denote as MnO₂-GM-Ni?.The maximum specific capacitance of MnO₂-GM-Ni electrode is 470.5 F g^-1 at a charge/discharge current density of 1 A g^-1.The capacitance retention is as high as 86%after 10,000 charge/discharge cycles at 2 A g^-1 which exhibited excellent cycling performance.Furthermore,the MnO₂-GM-Ni//GM-Ni asymmetric supercapacitor displays a maximum energy density of 35.3 Wh kg^-1 at a power density of 426 W kg^-1 and also a favorable cycling performance that 83.8%capacitance retention after 5000 cycles at a charge/discharge current density of 1 A g^-1.A unique nanostructure electrode consisting of RuO₂ nanoparticles with ultra-fine diameter?the mean size diameter is 1.9 nm?anchored on the surface of graphene nanosheets?GNS?and carbon nanotube?CNT?is prepared as a binder-free supercapacitor electrode through a two-step electrochemical routes.At first,free-standing GNS and CNT are directly deposited on the surface of carbon fiber cloth?CFC?to form a cross-linked film?GC?via a cathodic electrophoretic deposition.After the following electro-deposition process,the as-prepared GC film is uniform covered with RuO₂ nanoparticles.The 3D binder-free RuO₂-GNS-CNT-CFC?RuO₂-GC-CFC?hybrid electrode exhibits a high specific capacitance up to 480.3 F g^-1?based on the total mass of GNS,CNT and RuO₂?and remarkable cycling stability?89.4%capacitance retention after 10000 cycles?.Furthermore,the assembled symmetric supercapacitor exhibits a high energy density of 30.9 Wh kg^-1 and power density of14000 W kg^-1 with excellent stability performance?92.7%capacitance retention after 10000cycles?.