Electrochemical Capacitance Performance Of Cobalt/Nickel (Hydroxide) Oxides Electrodes

Recently,many researchers have focused on how to enhance the electrochemical performance of electrochemical capacitors and reduce the cost of electrodes.Although noble metal-oxide(e.g.RuO₂) and carbon yeild remarkedly high specific capacitance and/or power densities,capacitors based on these materials are much more costly.The capacitance of conducting polymer is satisfactory,but the poor stability and cycle property limit its commercial use.Therefore,other cheap transition-metal oxides that exhibit similar behavior, e.g.Co₃O₄,NiO,are thought of as the most ideally candidate(or alternative) electrode materials for electrochemical capacitors.This thesis consists of three parts:The purpose of the first chapter is not only to survey the research progress of electrochemical capacitors but also the fundamental principles,characterizations and applications of electrochemical capacitors,especially the recent progress of electrochemical capacitors using carbon,transition-metal oxide and conducting polymer as electrode materials and the study of hybrid supercapacitors.Based on all the above I put forward my purposes and researches in this field.The second chapter shows the electrochemical performance of the superapacitors based on Co₃O₄ by a hydrothermal microemulsion method.This chapter is divided into three parts.1.Cobalt oxide electrodes with novel morphologies were prepared via hydrothermal microemulsion.Electrochemical tests indicate that we can control the morphologies and electrochemical properties of materials.In addition,acetylene black doped in the Co₃O₄ electrode enhance its electrochemical properties.2.Cobalt and nickel mixed oxides were synthesized via a microemulsion-mediated hydrothermal methode at different molar ratios of Co/Ni.By using electrochemical measurements,it is found that the morphologies and electrochemical performance of electrodes have a close relationship with the amounts of Co and Ni.The third chapter,divided into two parts,mainly investigates the electrochemical capacitance performance of nickel hydroxide electrodes by hydrothermal microemulsion.1.β-Ni(OH)₂ electrodes were fabricated by hydrothermal microemulsion,using sodium dodecyl sulfate(SDS) as the surfactant.Electrochemical tests display the concentration of SDS has great influence on its morphology and electrochemical capacive performance.2.Nanowhisker-like spheres of hydrous nickel hydroxide were controlled synthesized by a microemulsion-mediated hydrothermal method.Tests show that the concentration of surfactant(Cetyltrimethylammonium bromide) and precipitation agent(urea) plays an important role in the morphologies of materials,and the outstanding capacitance of hydrous nickel hydroxides electrodes can be attributed to their loosely nanometer-scale whiskers.The fourth chapter shows the electrochemical properties of Co(OH)₂ electrocdes prepared by coordination homogeneous precipitation method.This chapter is divided into three parts:1.α-Co(OH)₂ particles were successfully prepared by coordination homogeneous precipitation method.All the results indicate that as-synthesizedα-Co(OH)₂,which possesses a flower-like architecture when adding surfactant Tween-80 has a better capacity.2.Co-Al double hydroxides were synthesized by coordination homogeneous precipitation method.The results display that the capacitive properties of electrodes doped with Al are better than those of pure Co(OH)₂ electrodes,and the capacitances of these composites electrodes were found approximately dependent on the molar ratios of Co/Al.3.A hybrid electrochemical capacitor has been designed with Co-Al double hydroxide and activated carbon as positive and negative electrodes,respectively.The results show that the hybrid electrochemical capacitor has excellent electrochemical performance.