secondary battery for hydrogen storage using Singlewalled Carbon Nanotubes electrodes
Won Seok Kim, Young Soo Park, Kwan Ku Jeon, Keun Soo Kim,
Kay Hyeok An, Jeong-Mi Moon, and Young Hee Lee
Department of physics, Sungkyunkwan University, Suwon 440-746, Kyunggi, South Korea
A new storage material with high capacity, light mass, and long cycle life has been strongly demanding for portable electronics, fuel cells and so forth. Large empty space inside the single-walled carbon nanotubes (SWCNTs) and large surface area open a possibility for hydrogen storage applications. Until now, it has been reported that hydrogen can be stored in SWCNTs from high-pressure approach that has limitation in battery application. However, electrochemical approach has several advantages for practical application. Here, we have investigated key factors for electrochemical hydrogen storage in SWCNTs to determine storage capability by controlling the amount of transition metals that are added during SWNTs synthesis. SWCNTs are synthesized with 20 wt% and 5 wt% of transition metals by arc discharge. The SWCNTs are compressed into a pellet with pressure of 1000 psi, pre-annealed at 300 °C in air for five hours for the purpose of removing amorphous carbons, and again heated at 900 °C for several hours in Ar gas in order to improve their crystallinities, which is confirmed from Raman spectroscopy. TGA analysis shows that ~50 wt% of metals remained in the pellet. The discharge storage capacity above 330 mAh/g (1.184 Hwt%) was obtained at a cutoff voltage of 0.8 V. We observed that the plateau region in the voltage scan, which is of critical importnace in practical application, was maintained during the constant-current discharge mode. The CV measurement also shows redox reaction peak near 1 V during discharge, in good agreement with the charge-discharge experiment.
Corresponding author : Young Hee Lee
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Keywords: Singlewalled carbon nanotubes, Raman spectroscopy, TGA, charge-discharge experiment, CV measurement.