Atmospheric-pressure plasma treatment to modify hydrogen storage properties of multiwalled carbon nanotubes

Abstract

We prepared multiwalled carbon nanotubes by a floating catalyst method using thermal chemical vapor deposition, but then the structures of the nanotubes were modified by the atmospheric-pressure plasma treatment to enable practical applications to hydrogen storage media. As is usually observed in multiwalled carbon nanotubes grown by thermal chemical vapor deposition, the as-grown multiwalled carbon nanotubes showed closed-cap structures and continuous walls that could not provide enough sites for hydrogen storage at ambient conditions. A thermal desorption spectra analysis showed that hydrogen was released at a temperature range of 100–150K, where the total amount of evolved hydrogen was 4.9wt%. However, after the atmospheric-pressure plasma treatment performed to open closed caps and create nanopores in multiwalled carbon nanotubes, it was found that the modified structures of the nanotubes released hydrogen not only at a subambient temperature range of 100–150K, but also at an ambient temperature range of 300–330K. The amount of released hydrogen was 5.1wt% and 0.6wt%, respectively.