| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 103 === Supercapacitors include a family of electrochemical capacitors, which contain no solid dielectric. According to the charge storage mechanism, supercapacitors are divided into: electric double layer capacitors (EDLC) and pseudocapacitors. Among them, pseudocapacitors can have capacitance ten times as much as that of EDLC. Metal oxides and conducting polymers are the commonly used materials for pseudocapacitors. This thesis study was focused on fabricating and characterizing copper-containing pseudocapacitors. In particular, rhomboid-shaped, copper-containing nanoplates, which had a chemical formula of [Cu-O-CH2-CH2-O], were synthesized using a polyol-mediated method. Copper oxide nanosheets were also grown on copper foil. Using nafion to bind the synthesized rhomboid nanoplates to a gold foil as the working electrode, the electrochemical pseudocapacitance of the nanoplates was studied. With the scan rate of 10 mV/s, cyclic voltammetry (CV) showed the specific capacitances of the rhomboid nanoplates and copper oxide nanosheets in 1M KOH to be 87.5 F/g and 53.6 F/g, respectively. The specific capacitances decreased at increasing scan rates, indicating that the migration and diffusion of electrolyte ions into the nanostructure materials affected their supercapacitor performance. The electrochemical performance of both rhomboid nanoplate and CuO nanosheets examined by CV showed the redox reactions, which hydroxide ions involved in. It would be results from the redox pseudocapacitance from hydroxide ions.
X-ray photoelectron spectroscopy (XPS) showed the presence of potassium ions in the rhomboid nanoplate electrode after CV. It suggested the alkali metal ion participation in the pseudocapacitance, which also resulted in larger specific capacitance decreases at increasing scan rates for rhomboid nanoplates than copper oxide nanosheets. While changing the supporting electrolyte from KOH to NaOH and LiOH, the rhomboid nanoplate showed higher specific capacitance of 128.7F/g and 189.7 F/g calculated by CV at scan rate 10 mV/sec. The XPS signal ratio of cations to copper ions increases with CV cycle revealed that the cations intercalated into rhomboid nanoplates within charge- discharge process. In addition to the redox pseudocapacitance, the intercalation pseudocapacitance was involved proved by the XPS spectra
|
|---|
