Influence of the pore size in multi-walled carbon nanotubes on the hydrogen storage behaviors

Activated multi-walled carbon nanotubes (A-MWCNTs) were prepared using a chemical activation method to obtain well-developed pore structures for use as hydrogen storage materials. The microstructure and crystallinity of the A-MWCNTs were evaluated by X-ray diffraction and Fourier transform Raman spectroscopy. The textural properties of the A-MWCNTs were investigated by nitrogen gas sorption analysis at 77 K. The hydrogen storage capacity of the A-MWCNTs was evaluated at 77 K and 1 bar. The results showed that the specific surface area of the MWCNTs increased from 327 to 495 m2/g as the activation temperature was increased. The highest hydrogen storage capacity was observed in the A-MWCNTs sample activated at 900 °C (0.54 wt%). This was attributed to it having the narrowest microporosity, which is a factor closely related to the hydrogen storage capacity. This shows that the hydrogen storage behaviors depend on the pore volume. Although a high pore volume is desirable for hydrogen storage, it is also severely affected if the pore size in the A-MWCNTs for the hydrogen molecules is suitable for creating the activation process.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The AT-800 and AT-900 samples were prepared by a chemical activation method at activation temperature of 800 and 900 °C, respectively. ► The AT-900 sample has the narrowest peak in comparison with the AT-800 sample, resulting from the overlap of the two peaks (Peak I and Peak II). ► This overlapping effect is due to the newly created micropores or shrinkages of pores in Peak II. So, these determining characteristics are essential for designing materials that are suitable for molecular hydrogen storage.