Influence of compressive strain on the hydrogen storage capabilities of graphene: A density functional theory study

TL;DR

This study demonstrates that applying 6% biaxial compressive strain to graphene significantly enhances its hydrogen storage capacity, achieving reversible adsorption with a high hydrogen uptake of 9.4% by density functional theory calculations.

Contribution

The paper introduces the use of compressive strain as a novel method to improve hydrogen adsorption in pristine graphene without doping or metal decoration.

Findings

At 6% biaxial compressive strain, graphene adsorbs 10 H₂ molecules.

The average binding energy per H₂ is -0.42 eV, suitable for reversible storage.

Hydrogen uptake reaches 9.4% with 20 H₂ molecules in a 4x4x1 supercell.

Abstract

Pristine graphene is not suitable for hydrogen storage at ambient conditions since it binds the hydrogen molecules only by van der Waals interactions. However, the adsorption energy of the hydrogen molecules can be improved by doping or decorating metal atoms on the graphene monolayer. The doping and decoration processes are challenging due to the oxygen interference in hydrogen adsorption and the clustering issue of metal atoms. To improve the hydrogen adsorption energy in pristine graphene, we have explored the hydrogen storage capabilities of graphene monolayer in the presence of compressive strain. We found that at 6 % of biaxial compressive strain, a 4*4*1 supercell of graphene can adsorb 10 H$_2$ molecules above the graphene surface. The average binding energy of H$_2$ for this configuration is found to be -0.42 eV/H$_2$, which is very suitable for reversible hydrogen adsorption. We propose that a 4*4*1 supercell of graphene can adsorb a total number of 20 H$_2$ molecules leading to a high hydrogen uptake of 9.4 %. The interaction between orbitals of carbon and hydrogen atoms and the charge transfer process have been studied by plotting the partial density of states and surface charge density plots. The electronic density around the C-C bonds of graphene increases in the presence of compressive strain, due to which hydrogen molecules are strongly adsorbed.