Surface state of carbon materials and accumulation of hydrogen in multiwalled carbon nanotubes

Literature data on the nature of oxide structures formed on the surface and in the bulk of carbon materials, including carbon black, multiwalled nanotubes (MWNTs), and carbon fiber are generalized. Positive and negative effects of oxide structures on the properties of MWNTs and the possibilities of their practical utilization are considered. The probable nature of the surface and bulk oxide structures is discussed. The effect of the cathodic polarization value and the nature and composition of the electrolyte on the accumulation of hydrogen in MWNTs directly applied on a steel membrane or involved in an Epoxy-resin-based composite is studied. In an acidic environment (x M HCl + (1 − x) M LiCl), the amount of hydrogen accumulated by carbon nanotubes in a Fe/MWNT system is shown to vary in a range of 3–13.8 wt % and increase with an increase in the acidity of the environment at the cathodic shift of the potential by 0.2 V from the steady-state value (in the absence of external field). In an alkaline environment (1 M KOH), the amount of absorbed hydrogen is 3.5–15 wt % depending on the cathodic polarization (up to 0.4 V) and the weight of multiwalled nanotubes.