Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: A density-functional theory study

Abstract

We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage Theta [from 0.11 to 2.0 monolayers (ML)] and adsorption sites. In the coverage range 0 < Theta < 1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendency to the formation of H islands (clusters) when increasing the coverage within the region 0 < Theta < 1.0. The on-surface diffusion path energetics of atomic hydrogen as well as the activation barriers for hydrogen penetration from the on-surface to the subsurface sites are also presented at low coverage. At high coverage of 1.0 < Theta < or = 2.0, it is found that the coadsorption configuration with 1.0 monolayer of H residing on the surface fcc sites and the remaining (Theta-1.0) monolayer of H occupying the subsurface tetra-I sites is most energetically favorable. The resultant H-Mg-H sandwich structure for this most stable coadsorption configuration displays similar spectral features to the bulk hydride MgH(2) in the density of states. The other properties of the H/Mg(0001) system including the charge distribution, the lattice relaxation, the work function, and the electronic density of states are also studied and discussed in detail. It is pointed out that the H-Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character.

Modeling reaction pathways for hydrogen evolution and water dissociation on magnesium

“…This structure is energetically favorable, and the computed binding energy is -0.20 eV, relative to H . This is consistent with other theoretical studies that have computed favorable binding energies for atomic H absorbed at subsurface sites [54][55][56]. Moreover, it is reasonable for an arrangement like that shown in Fig.…”

First-Principles Study on a Potential Hydrogen Storage Medium of Mg/TiAl Sandwiched Films

“…The calculated PDOSs are well consistent with other theoretical results. 30,31 High similarity on the PDOSs between the surface and bulk Mg atoms (Mg1 and Mg2) is noted. Both show a main bonding peak at −5.0 eV.…”

“…The H−Mg chemical bonding during surface hydrogenation displays a mixed ionic/ covalent character. 31 The compressive (negative) strain facilitates the formation of the H−Mg−H trilayers due to the fact that the lattice constant of H−Mg−H trilayer is shorter than that of pure Mg. 32 Furthermore, studies on the absorption/desorption of hydrogen on Ti or TiAl are reported . 33,34 Hydrogen atoms prefer to pair up and form clusters in Mg, but they are likely to occupy the sites apart as far as possible in Ti.…”

“…The trilayers display similar features in the density of states comparing to the bulk MgH 2 . The H–Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character . The compressive (negative) strain facilitates the formation of the H–Mg–H trilayers due to the fact that the lattice constant of H–Mg–H trilayer is shorter than that of pure Mg …”

Boron nitride formation on magnesium studied byab initiocalculations

“…Some earlier ab initio investigations concerning adsorbates on magnesium have concentrated on the ability of magnesium to break the hydrogen bond and to store atomic hydrogen. [14][15][16][17] This work is organized as follows: In Sec. II we first consider in detail the present state of the art method for producing BNNTs and then explain our strategy for studying boron-nitride chemistry on magnesium.…”