Carbon Spheres And Hollow SnO₂Spheres:Fabrication And Electrochemical Property

In recent years, supercapacitors, as charge-storage devices providing with high-power density, resistance low equivalent series, long cyclic-life and good environmental compatibility, have attracted tremendous attention. In order to research this, supercapacitors consisted of electroactive materials have to under extensive investigation due to high capacitive and high energy characteristics. At present, the materials studied have essentially been of three types (i) carbon materials of high surface area,(ii) metal oxides,(iii) conducting polymers. In this research, the obtained carbon microspheres from carbonizing resorcinol-formaldehyde (RF) resin and hollow SnO2microspheres from calcining tin/polymer colloidal spheres, are further investigated for preparation processes and electrochemical properties, as supercapacitor electrode materials, with several analytical tools. The main contributions and innovations of this thesis are as follows:1. Carbon spheres:with boric acid (H3BO3), hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), ammonia (NH3·H2O), sodium hydroxide (NaOH) as a catalyst, resorcinol and formaldehyde as the precursor, are prepared various morphology and particle size of RF resin microspheres by hydrothermal synthesis method. Among the catalysts investigated in this work, ammonia is the most efficient one for preciously controlling the size and morphology of the RF resin microspheres. Moreover, the concentrations of ammonia and precursors play important roles in forming the RF resin microspheres. Furthermore, when the concentration of ammonia is0.433mol/L and the concentration of resorcinol is0.485mol/L (the concentration ratio of precursors keeps0.1), the average diameter of the RF microspheres is0.98um. Carbon microspheres derived from carbonizing the RF microspheres at800℃are evaluated with several electrochemical analytical tools, as the supercapacitor electrode material. It presents the low resistance value (R) of0.5Q in6mol/L KOH electrolyte. The maximum specific capacitance of the electrode measured from cyclic voltammetry is up to175.9F/gat a scan rate of1mV/s. The specific capacitance only decays5.6%after500cycles, which indicates that the sample possesses excellent cycle durability. The present study clearly shows that highly monodispersity carbon microspheres from RF microspheres are electroactive materials with reducing mass transport resistance and improving supercapacitor performance reliability. 2. Hollow SnO2microspheres:with using different tin compounds, including stannous sulfate (SnSO4), stannous chloride dihydrate (SnCl2·2H2O) and stannic chloride pentahydrate (SnCl4·5H2O), as precursors of SnO2, resorcinol and formaldehyde as the precursors of carbon microspheres, hollow SnO2microspheres are prepared from calcining tin/polymer colloidal spheres in air. The as-prepared composites are evaluated as the supercapacitor electrode material with several electrochemical analytical tools in1mol/L H2SO4solution. Composites obtained with SnSO4and SnCl2·2H2O as precursors show relatively lower specific capacitances of395F/g and347F/g, respectively. The specific capacitance of SnO2from SnCl4·5H2O as the precursor is up to663F/g. High specific surface area and hollow structure of SnO2microspheres can facilitate the rapid transport of electrolyte ions and improve capacitive character. It is expected that hollow SnO2microspheres are the promising redox supercapacitor materials.