Preparation Of Metal(Hydro-) Oxides And Composites For Supercapacitor Electrodes In Rotor Stator Reactor

Due to the high micromixing and mass transfer efficiency,ease of scale-up,the Rotor-Stator Reactor(RSR)has unique advantages in the preparation of nano-materials in a large-scale.As a new energy device,supercapacitor has the characteristics of high power density,good stability and environmental friendliness.However,the electrochemical properties of the electrode materials need to be improved.The metal(hydro-)oxides and their composites were prepared in RSR and the electrode materials with large surface area,good composition uniformity,and high electrochemical performance were obtained.Using specific surface area and electrochemical performance as the main evaluation index,this dissertation optimized the process parameters in the preparation of manganese dioxide,nickel-cobalt hydroxide and nickel-cobalt carbonate hydroxide in a RSR and then obtained their composite materials with carbon nanotubes or graphene.The electrode materials exhibit good performance in the application of electrochemical capacitors or battery-like devices.In addition,the flexible electrodes composed of a current collector and an active electrode were screen printed and then were assembled to build a solid-state supercapacitor so as to assess their electrochemical properties.These works laid the foundation for the application of the electrode materials prepared with RSR in flexible solid-state supercapacitors.The main contents and results of this dissertation are as following:1.Manganese dioxide were prepared with potassium permanganate and manganese nitrate as raw materials and the parameters such as reaction temperature,reactant concentration(based on potassium permanganate),feeding speed,and rotating speed of RSR were studied.The suitable parameters to prepare manganese dioxide with high surface area and good electrochemical properties were determined.The MnO2//MnO2 symmetric supercapacitor,MnO2//AC(activated carbon)and MnO2//G(graphene)asymmetric supercapacitors in a coin type were assembled using manganese dioxide,activated carbon or graphene as electrode materials and their electrochemical properties were evaluated.The optimum conditions were determined as the reaction temperature of 50?,RSR rotating speed of 900 rpm,volumetric flow rate of KMnO4 and Mn(NO3)2 of 11.64?12.84 L h-1,reactant(KMnO4)concentration of 0.03 mol L-1.The MnO2//AC supercapacitor had the maximum specific capacitance of 241.94 F g-1 at a current density of 0.5 A g-1 and the energy density was 27.23 Wh kg-1 with a power density of 225 W kg-1.2.Nickel-cobalt double hydroxides were prepared in RSR with the co-precipitation method and the effects of the reactant concentration(based on the total molar concentration of nickel and cobalt salt)and the Ni:Co ratio on the electrochemical properties of the hydroxides were studied and suitable process parameters were determined.The electrochemical performance of the nickel-cobalt double hydroxides electrodes for supercapacitors was tested with the two-electrode method.The band gap of the nickel hydroxide doped with different cobalt content was calculated using density first theory(DFT)method,which explained theoretically that the cobalt doping can improve the electrochemical performance of nickel hydroxide.The specific capacitance of the NiCo LDH electrode with Ni:Co ratio of 2:1 was 176.7 mA h g-1 at a current density of 1 A g-1.3.Nickel-cobalt carbonate hydroxides were prepared in RSR with sodium hydroxide,sodium carbonate,nickel sulfate and cobalt sulfate as raw materials.The effects of the parameters such as reaction temperature,reactant concentration(based on the total molar concentration of the nickel and cobalt salts),RSR rotating speed and Ni:Co ratio on the electrochemical performances of nickel-cobalt carbonate hydroxides were studied.The optimum conditions were determined as the total reactant concentration of 0.1 mol L-1,reaction temperature of 60?,RSR rotating speed of 1400 rpm,and Ni:Co ratio of 4:1.The specific capacitance of the corresoponding NiCoCH electrode was 218.8 mA h g-1 at a current density of 1 A g-1.4.The MnO2-CNT(carbon nanotube),MnO2-GO(graphene oxide)and NiCo LDH-CNT were prepared in-situ and MnO2-G composite by self-assembly.The effect of CNT and graphene oxide(GO)contents on the electrochemical properties of these composite materials was studied.The optimal doping amount was 1 wt%CNT for Mn02-CNT,0.5 wt%CNT for MnO2-GO and 3.23 wt%CNT for NiCoLDH-CNT.5.Activated carbon and graphene ink were prepared.The silver conductive ink and the carbon or graphene ink were screen printed onto PET substrate in sequence to fabricate a supercapacitor electrode.The flexible sandwich and inplane solid-state supercapacitors were assembled seperately using PVA-H2SO4 gel as electrolyte.The working voltage of a single device was 0.8 V.The specific capacitance of the sandwich graphene-based supercapacitors was 190.6 F g-1 at a current density of 0.5 A g-1.The light emitting diode was lit up with such supercapacitors connected in series.