Electrochemical Capacitance Of Composite Electrodes Based On Tio₂ Nanotubes And Carbon Nanotubes

Many researches in the area of electrochemical supercapacitors have been made focusing on the development of electrode materials that have high specific surface area and electrochemical properties in suitable electrolytes, such as carbon, transition-metal oxide and conducting polymer. In general the capacitance of carbon is low due to the energy storage by utilizing the double-layer capacitance arising from the charge separation at the electrode-electrolyte interface. The capacitance of conducting polymer is satisfactory, but the poor stability and cycle property limit its commercial use. Many transition-metal oxides are known as excellent electrode materials for supercapacitors with charge-storage mechanisms based predominantly on pseudo-capacitance. Although ruthenium-oxide system gives very high specific capacitance, it has the inherent disadvantage of high price and toxicity. Therefore, other cheap and environmentally benign transition-metal oxide and metal oxides/carbon composites are thought of as the most ideally candidate (or alternative) electrode materials for supercapacitors.This thesis consists of three chapters. The purpose of the first chapter is not only to survey the research progress of supercapacitors but also the history, properties and preparation of supercapacitors, especially the recent progress of researches on supercapacitors using transition-metal oxide. Based on this information I put forward my purposes and researches in this filed.The second chapter shows the preparation and super-capacitive properties of composite materials based on TiO2 nanotubes. This chapter is divided into three parts. 1. MnO2·nH2O/TiO2 nanotubes composites with different ratios ofα-MnO2·nH2O and TiO2 nanotubes were prepared by chemical co-precipitation method. Electrochemical tests indicate that the composite materials can prove to be excellent electrodes for supercapacitors, when the weight ratio ofα-MnO2·nH2O and TiO2 nanotubes is 6:4. 2. MnO₂·nH₂O/TiO₂ nanotubes composites doped with cobalt or nickel used as electrode materials were prepared by chemical co-precipitation method. The results show that the amounts of Co and Ni in samples have great influence on their electrochemical capacities. The electrode doped with Co has better capacitance property than that of doped with Ni.3. Me double hydroxide(Me=Co+Ni/TiO₂)nanotubes were prepared by chemical co-precipitation method. By using electrochemical measurements, it is found that TiO₂ nanotubes increase the dispersion of active materials and enhance the capacitance.The third chapter shows the preparation and super-capacitive properties of composite materials based on carbon nanotubes film electrode. This chapter is divided into four parts.1. Nickel oxide/carbon nanotubes (NiOx/CNT) film nanocomposite electrode was prepared by electrophoretically deposition. Electrochemical tests show that these nanocomposite electrodes have excellent electrochemical properties. The improved electrochemical performance of the NiOx on CNT film substrate can be attributed to its electrode construction.2. Cobalt hydroxide/carbon nanotubes (Co(OH)₂/CNT) film composite electrode was prepared by electrophoretically deposition. Electrochemical tests show that the electrodes have excellent electrochemical properties.3. A hybrid supercapacitor has been designed with CoxO/CNT composite and active carbon as positive and negative electrodes, respectively. The results indicated that the hybrid supercapacitor has excellent capacitive performance and good cycle life.4. Nickel and cobalt mixed oxides (denoted as (Ni+Co)Ox) were anodically deposited onto carbon nanotubes (CNT) film substrate. The results indicated that these composites have excellent electrochemical properties, and the specific capacitances of these composites electrode were found approximately dependent on the mole ratio of Ni/Co deposition solutions.