Hydrogen on graphene under stress: Molecular dissociation and gap opening

TL;DR

This study uses density functional calculations to show that stress significantly lowers the barrier for hydrogen dissociation on graphene, alters the reaction energetics, and induces a band gap at certain coverages, aligning with experimental observations.

Contribution

It demonstrates how applying stress to graphene can facilitate hydrogen dissociation and induce a band gap, providing insights into tunable electronic properties of graphene-hydrogen systems.

Findings

Stress reduces hydrogen dissociation barrier by a factor of six.

Reaction becomes exothermic under stress, matching experimental timescales.

A 0.5 eV band gap appears at specific hydrogen coverages.

Abstract

Density functional calculations are employed to study the molecular dissociation of hydrogen on graphene, the diffusion of chemisorbed atomic species, and the electronic properties of the resulting hydrogen on graphene system. Our results show that applying stress to the graphene substrate can lower the barrier to dissociation of molecular hydrogen by a factor of six, and change the process from endothermic to exothermic. These values for the barrier and the heat of reaction, unlike the zero stress values, are compatible with the time scales observed in experiments. Diffusion, on the other hand, is not greatly modified by stress. We analyse the electronic structure for configurations relevant to molecular dissociation and adsorption of atomic hydrogen on a graphene single layer. An absolute band gap of 0.5 eV is found for the equilibrium optimum configuration for a narrow range of coverages ($\theta \approx 0.25$). This value is in good agreement with experiment [Elias et al., Science {\bf 323}, 610 (2009)].