Synthesis and Characterization of Copper-containing Nanostructures as Supercapacitor Materials

本論文研究含銅奈米結構的鑑定及其超級電容的行為表現，主要研究含銅結構的菱形奈米板片，其具有[Cu-O-CH2-CH2-O]的結構，並利用nafion將奈米板片固定於金箔上做為工作電極，另外與之比較的是在銅箔上生長的氧化銅奈米薄板。兩者同樣利用1 M KOH做為電解液時，利用循環伏安法（CV）探討的超級電容表現，可分別得到為87.5及53.6 F/g。且兩者在CV上的電化學行為可知其主要充放電行為是來自氧化還原造成的贋電容( pseudocapacitance)。 利用X-ray光電子能譜( XPS )發現在做完CV的菱形奈米板片的電極表面中有鉀離子的存在，但氧化銅奈米薄板中則沒有。且改為利用NaOH或LiOH做為電解液時，菱形奈米板片的電容值會分別增加為128.7及189.7 F/g。在進行完不同條件的CV後，會發現鹼金屬陽離子相對銅離子的訊號比例會有增長的趨勢，故推論出鹼金屬陽離子的嵌入( intercalation )行為會對菱形奈米板片的超級電容行為有所助益。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 spectr