Effects of heat treatment on materials characteristics and hydrogen storage capability of multi-wall carbon nanotubes

Heat treatment on multi-wall carbon nanotubes (CNTs) in ammonia gas was performed in this study. Effects of heating temperature (up to 1000 °C) on material characteristics of the CNTs were systematically investigated. Microstructure of the CNTs was examined using a transmission electron microscope. In addition, their crystallinity and specific surface area were evaluated with a Raman spectrometer and a nitrogen gas sorption analyzer, respectively. It was found that hydrogen storage performance of the CNTs clearly depended on their microstructure and crystallinity, which can be modified by the heat treatment. The hydrogen storage capacity of the as-received CNTs, measured with a high-pressure microbalance under 6.89 MPa, was only 0.39 wt.%. However, this value can be significantly improved to be 2.9 wt.% when the CNTs underwent a heat treatment conducted in the ammonia atmosphere at 1000 °C.