Hydrogen adsorption on activated carbon nanotubes with an atomic-sized vanadium catalyst investigated by electrical resistance measurements

Activated multi-walled carbon nanotubes were prepared with appended vanadium as a hydrogen storage medium. The pore structure was significantly improved by an activation process that was studied using Raman spectroscopy, field emission transmission electron microscopy and pore analysis techniques. X-ray photoelectron spectroscopy and X-ray diffraction results reveal that the vanadium catalyst was introduced into the carbon nanotubes in controlled proportions, forming V8C7. The improved pore structure functioned as a path through the carbon nanotubes that encouraged hydrogen molecule adsorption, and the introduced vanadium catalyst led to high levels of hydrogen storage through the dissociation of hydrogen molecules via the spill-over phenomenon. The hydrogen storage behavior was investigated by electrical resistance measurements for the hydrogen adsorbed on a prepared sample. The proposed mechanism of hydrogen storage suggests that the vanadium catalyst increases not only the amount of hydrogen that is stored but also the speed at which it is stored. A hydrogen storage capacity of 2.26 wt.% was achieved with the activation effects and the vanadium catalyst at 30 °C and 10 MPa.

Graphical abstractThe improved pore structure worked as a route for easy adsorption of hydrogen molecules in the carbon nanotubes, and the introduced vanadium catalyst played a role in high-efficiency hydrogen storage through the dissociation of hydrogen molecules in the spill-over phenomenon.Download full-size imageHighlights► Investigation of hydrogen storage behavior by changes in electrical resistance. ► Creation of a pathway for hydrogen storage inside MWCNTs. ► Improvement of the specific surface area for hydrogen adsorption sites. ► Size-controlled vanadium catalyst to attract the electrons in the hydrogen molecule.