Transition Metal-Decorated Nanotubes and C 60; high-capacity hydrogen storage medium
Introduction | Dissociative Absorption of H2 | Molecular Absorption | 4th top-H2 | The lowest energy isomer | Bonding Mechanism | Does Pt/Pd also work? | MD simulations | High concentration metal-coverages | Ti-decorated C60 | ConclusionsThe Lowest Energy Configuration for 4H2-t80Ti system
The final optimized structures shown in previous slides need not be the global minimum. Among many different isomers tried for the four-H 2 system, we found a very symmetric configuration (denoted as t80Ti- 4H 2) that is 0.1 eV lower in energy than t80TiH 2- 3H 2 (Fig. 2a). Here all four hydrogen molecules stay intact and benefit equally from bonding with the Ti atom. The average H-H bond distance is about 0.84 Å and each molecule has a charge of about 0.32 e. The average binding energy per H 2 molecule is 0.54 eV, which suggests that the bonding is an unusual combination of chemisorption and physisorption. Also note that each of the four H 2 molecules is located just above one of the four carbons of the hexagon over which the Ti atom is bonded. This suggests that carbon atoms also play an important role in the binding.
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