Ab Initio Simulations of the Kinetic Properties of the Hydrogen Monomer on Graphene

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 π bond of the hydrogenated graphene during the desorption and diffusion of the hydrogen monomer were 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, the activation energy, and the jump frequency of the hydrogen monomer. The kinetic properties of the hydrogen-isotope monomers were simulated under conditions of annealing for 10 min 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.

Hydrogen transport on graphene: Competition of mobility and desorption

“…However, most calculations predict the hydrogen migration barrier to be lower than that for desorption. In some cases, the predicted barriers (1.035, 40 1.01, 16 0.98, 22 or 0.94 eV 41 ) are only slightly lower than the detrapping energy; in others, the difference is more pronounced. For example, the diffusion barrier of 0.78 eV has been predicted by DFT calculations 42 and tight-binding molecular dynamics simulations.…”

Tuning Hydrogen Adsorption on Graphene by Gate Voltage

“…43 On the other hand, n-type doping increases the activation energy for diffusion, 10 so that the activation energy for diffusion of hydrogen monomers becomes comparable to or larger than that for desorption, and therefore, on neutral or n-type graphene, hydrogen monomers will not diffuse to form hydrogen dimers, but rather desorb. 44 Combining the above two effects derived from the theoretical calculations, we can conclude that p-type doping promotes conversion from hydrogen monomers to dimers. This explains the experimental results.…”

“…It is well known that H with its lower mass desorbs and diffuses on graphene more easily than D, due to the difference of their zero point energies. 34,44,45,46 According to a previous theoretical calculation, 10 The clear dependence of hydrogen adsorption energy on doping implies that external perturbations, such as gate voltage, which change the charge density of graphene, can be used to tune the stability of adsorbed hydrogen on graphene.…”

Electric field manipulated reversible hydrogen storage in graphene studied by DFT calculations

“…In addition, the diffusion also increases the energy of the system. Therefore, H atoms are relatively stable on the N‐doped graphene surface comparing with the case of a single H atom adsorbed on pristine graphene, where diffusion barrier is ∼1 eV .…”