Adsorption and dissociation of hydrogen molecules on bare and functionalized carbon nanotubes

TL;DR

This study uses first-principles calculations to explore how hydrogen molecules interact with bare and functionalized carbon nanotubes, revealing that transition metal functionalization significantly enhances hydrogen adsorption and dissociation, which is promising for storage applications.

Contribution

It provides detailed insights into how transition metal atoms like Pt and Pd modify hydrogen adsorption and dissociation on carbon nanotubes, advancing understanding for hydrogen storage technologies.

Findings

Bare SWNTs have weak physisorption of H2, unaffected by curvature or Li coadsorption.

Pt functionalization enables dissociative and molecular chemisorption of H2, with dissociation favored under certain conditions.

Transition metals on SWNTs significantly improve hydrogen adsorption and dissociation, relevant for storage applications.

Abstract

We investigated interaction between hydrogen molecules and bare as well as functionalized single-wall carbon nanotubes (SWNT) using first-principles plane wave method. We found that the binding energy of the H$_{2}$ physisorbed on the bare SWNT is very weak, and can be enhanced neither by increasing the curvature of the surface through radial deformation, nor by the coadsorption of Li atom that makes the semiconducting tube metallic. Though the bonding is strengthened upon adsorption directly to Li atom, yet its nature continues to be physisorption. However, the character of the bonding changes dramatically when SWNT is functionalized by the adsorption of Pt atom. Single H$_{2}$ is chemisorbed to Pt atom on the SWNT either dissociatively or molecularly. If Pt-SWNT bond is weakened either by displacing Pt from bridge site to a specific position or by increasing number of the adsorbed H$_{2}$, the dissociative adsorption of H$_{2}$ is favored. For example, out of two adsorbed H$_{2}$, first one can be adsorbed dissociatively, second one is chemisorbed molecularly. The nature of bonding is weak physisorption for the third adsorbed H$_{2}$. Palladium also promotes the chemisorption of H$_{2}$ with relatively smaller binding energy. Present results reveal the important effect of transition metal atom adsorbed on SWNT and advance our understanding of the molecular and dissociative adsorption of hydrogen for efficient hydrogen storage.