Carbon nanotubes ( CNTs ) are attracting worldwide attention as hydrogen electrodes/suppliers to electrochemical energy storage devices, such as fuel cells, and super capacitors, to come true the environmental friendly world. However, several kinetic problems of CNT electrode remain to be solved before practical use is possible. In this study, the film electrodes of vertically aligned multiwall carbon nanotube ( MWNT ) synthesized by catalytic chemical vapor deposition were employed for electrochemical hydrogen charging/discharging experiments, to correctly evaluate the electrode performances and to better understand the electrode kinetics. The current-potential curves during charging/discharging were studied using cyclic voltammetry. A clear reproducible anodic peak for the oxidation of hydrogen in the electrode was found between -0.9 V and -0.7 V. The heat treatments at 400℃ under the air atmosphere produced significant changes in the anodic peak whose behavior reflects electrochemical kinetic properties and hydrogen storage capacity. The electrochemical impedance spectroscopy measurements were conducted successfully on the electrodes under the potentiodynamic polarization at the scan rate of 0.1 mV/s. The impedance spectra consisted of a small semicircle at high frequencies and a large depressed semicircle at low frequencies. Around the -0.85 V, the total reaction resistance reached a minimum. An equivalent circuit for the aligned MWNT electrode was proposed to elucidate the reaction mechanism for electrochemical hydrogen charging/ discharging.
配向性炭素ナノチューブの電気化学的エネルギー変換デバイスへの展開
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