Abstract
In this thesis study, it was to investigate and compare the differences of the morphology and electrochemical properties of the carbon nanotubes/MnO2 nanocomposite electrodes with normal- and pattern-type carbon nanotubes (CNTs). Owing to the highly dense character of normal-type CNTs, which prevents the electrolyte ions from penetrating into the inside of electrodes, MnO2 tend to aggregate onto the top of the CNTs. In contrast, the pitches in pattern-type CNTs can provide enough space for electrolyte ions to diffuse into electrodes, which allows MnO2 being uniformly electrodeposited onto the side area of the CNTs. Thus, pattern-type nanocomposite electrodes are expected to exhibit improved electrochemical properties. The CNTs were grown on normal and patterned Si substrates by microwave plasma-enhanced chemical vapor deposition, followed by a hydrophilic treatment in HNO3 solution. Then, the CNT electrodes were placed in 10 mM KMnO4 to deposit MnO2 onto the CNTs by cyclic voltammetry. The potential range was applied between -1 and 1 V and the depositing scan rate was 100 mV/s. By changing the deposition cycle number and the separation between arrayed CNTs, optimization of the nanocomposite electrodes has been achieved. The areal specific capacitance and long time stability of all nanocomposite electrodes were analyzed using cyclic voltammetry. The electrolyte was 2 M Na2SO4. The potential range was applied between 0 and 0.9 V and the scan rate was applied between 10 and 200 mV/s. The composition structure and morphology of the nanocomposite electrodes were characterized by scanning electron microscopy and Raman spectroscopy. It was found MnO2 could be uniformly deposited onto the top and sidewalls of the pattern-type CNTs with 20 m pitches, and the resulting nanocomposite electrode exhibited the best electrochemical properties. The optimized areal specific capacitances of normal and pattern-type nanocomposite electrodes, at 10 mV/s scan rate, were 14.22 and 332.85 mF/cm2 respectively; the latter is about 23 times of the former. In addition, the best pattern-type nanocomposite electrode maintained 96 % of the initial capacitance at 1,000th cycle, indicating its potential electrode material application in supercapacitors.