Molecular and dissociated adsorption of hydrogen on TiC6H6

Abstract

The dissociation of H2 molecule on metal-decorated carbon-based materials is a widespread phenomenon. And it is controversial that the dissociation of H2 molecule had significant effects on the hydrogen storage capacity. In this paper, comprehensive and detailed researches on the adsorption, dissociation and desorption of H2 molecules on the complex TiC6H6 were performed using Coupled-Cluster theory.We found that the dissociation of the H2 on TiC6H6 almost has no effect on the maximum number of adsorbed H2 but weakens stepwise adsorption energies of the later H2 molecules. The adsorption pathway is complicated due to the transformations of adsorption structures. The adsorption pathway along TiC6H6→1a→2a→3a pathway will be more favorable thermodynamically at room temperature. The most favorable desorption pathway is 3b→2b→1b→1a→TiC6H6, and its rate-determining step is the transition from 1b to 1a. These results indicate that the adsorption and desorption of hydrogen molecules on TiC6H6 follow different pathways due to dissociation of H2 molecules. Once the three H2 are completely liberated, the TiC6H6 system is ready to restart the absorption/desorption process again. In addition, by using CCSD(T) calculations as benchmark, the predictions using the B3LYP functional is valid for hydrogen sorbent materials including TiC6H6.