Effect of electrochemical treatment on structural properties of conical carbon nanotubes

Interaction of multiwalled conical carbon nanotubes (CNTs) with hydrogen during their electrochemical treatment was studied by galvanostatic measurements and Raman spectroscopy. The structural changes occurring in the conical walls of the CNTs in consequence of the hydrogenation were investigated by using X-ray diffraction (XRD). The results obtained show that hydrogen sorption by conical CNTs is reversible. XRD studies revealed that the electrochemical hydrogenation leads to a change in the diffraction peak profile (2θ=26^°) and its position corresponding to the interplanar distance in conical CNTs. The results indicate structural changes occurring in the conical walls of the CNTs during hydrogenation. We assume that these structural changes can be caused by the hydrogen intercalation into the interplanar spaces of conical CNTs. Thus, the charge/discharge and structure data can be explained by the existence in this system of physically adsorbed molecular hydrogen and chemically bound atomic hydrogen.