Ab initio simulations of the kinetic properties of the hydrogen monomer on graphene

TL;DR

This study uses ab initio simulations to analyze the kinetic properties of hydrogen monomers on graphene, revealing isotope effects and the significance of vibrational zero-point energy corrections in desorption and diffusion processes.

Contribution

It introduces a comprehensive quantum-mechanical approach combining DFT, perturbation theory, and transition state theory to study hydrogen monomers on graphene, highlighting isotope effects and vibrational corrections.

Findings

Lower-mass hydrogen isotopes desorb and diffuse more easily.

Vibrational zero-point energy significantly affects activation energies.

Results align with experimental observations.

Abstract

The understanding of the kinetic properties of hydrogen (isotopes) adatoms on graphene is important in many fields. The kinetic properties of hydrogen-isotope (H, D and T) monomers were simulated using a composite method consisting of density functional theory, density functional perturbation theory and harmonic transition state theory. The kinetic changes of the magnetic property and the aromatic $\pi$ bond of the hydrogenated graphene during the desorption and diffusion of the hydrogen monomer was discussed. The vibrational zero-point energy corrections in the activation energies were found to be significant, ranging from 0.072 to 0.205 eV. The results obtained from quantum-mechanically modified harmonic transition state theory were compared with the ones obtained from classical-limit harmonic transition state theory over a wide temperature range. The phonon spectra of hydrogenated graphene were used to closely explain the (reversed) isotope effects in the prefactor, activation energy and jump frequency of the hydrogen monomer. The kinetic properties of the hydrogen-isotope monomers were simulated under conditions of annealing for 10 minutes and of heating at a constant rate (1.0 K/s). The isotope effect was observed; that is, a hydrogen monomer of lower mass is desorbed and diffuses more easily (with lower activation energies). The results presented herein are very similar to other reported experimental observations. This study of the kinetic properties of the hydrogen monomer and many other involved implicit mechanisms provides a better understanding of the interaction between hydrogen and graphene.