Hydrogen-induced disintegration of fullerenes and nanotubes: An ab initio study

We use ab initio density-functional calculations to study hydrogen-induced disintegration of single-wall and multiwall carbon fullerenes and nanotubes. Our results indicate that hydrogen atoms preferentially chemisorb along lines in $s{p}^2$ bonded carbon nanostructures, locally weakening the carbon bonds and releasing stress. For particular structural arrangements, hydrogen helps to relieve the accumulated stress by inducing stepwise local cleavage leading to disintegration of the outermost wall.

Figure 1

(Color online) Equilibrium structure and bonding character in H-covered fullerenes and nanotubes. (a) Hydrogen chemisorption on the ${\text{C}}_{960}$ fullerene along strained lines with larger curvature. (b) Lines of chemisorbed hydrogen, shown in end-on and side views, yield the most stable adsorption on the (6,6) carbon nanotube. (c) Relaxed atomic structure near a line of chemisorbed hydrogen atoms. (d) Difference charge density $\Delta \rho$ indicating hydrogen-induced $s{p}^2\to s{p}^3$ local bonding change in graphitic nanocarbons. Contours of $\Delta \rho$ in the plane indicated in (c) are superimposed with the atomic lattice.

Figure 2

Zipper mechanism of hydrogen-induced disintegration of strained $s{p}^2$ carbon nanostructures. (a) Periodically warped graphene as model strained system. (b) Optimum structure and energetics for breaking a bond pair. (c) Sequence of bond cleavages resulting in a crack.

Figure 3

Hydrogen-assisted disintegration of (a) the ${\text{C}}_{240}$ fullerene and (b) the (6,6) carbon nanotube. Structural snapshots along the optimum reaction pathway are depicted in the left panels. The structural transformations of the nanotube in (b) are shown in end-on view. Carbon atoms are shown as gray and hydrogen atoms as larger black spheres. The right panels show the total-energy change in the system with the data points corresponding to the structures in the left panels.