Locating the rate-limiting step for the interaction of hydrogen withMg(0001)using density-functional theory calculations and rate theory

Abstract

The dissociation of molecular hydrogen on a Mg͑0001͒ surface and the subsequent diffusion of atomic hydrogen into the magnesium substrate is investigated using Density Functional Theory (DFT) calculations and rate theory. The minimum energy path and corresponding transition states are located using the nudged elastic band method, and rates of the activated processes are calculated within the harmonic approximation to transition state rate theory, using both classical and quantum partition functions based atomic vibrational frequencies calculated by DFT. The dissociation/recombination of H 2 is found to be rate-limiting for the ab-and desorption of hydrogen, respectively. Zero-point energy contributions are found to be substantial for the diffusion of atomic hydrogen, but classical rates are still found to be within an order of magnitude at room temperature.

Atomic Hydrogen Diffusion in Novel Magnesium Nanostructures: The Impact of Incorporated Subsurface Carbon Atoms

“…The hydrogenation of Magnesium involves molecular hydrogen dissociating on the Mg surface in the first step, followed subsequently by diffusion of the dissociated H atoms into the subsurface fcc sites through the fcc channels [17,32]. The former process in the presence of incorporated sub-surface carbon has been characterised for the first time in our previous work [20].…”

“…As shown in ref. [17,32], the most plausible diffusion pathway is the diffusion of atomic H from an hcp to a fcc site on the Mg(0001) surface and then to the subsurface fcc site. To explore this process in the presence of incorporated carbon, a series of NEB calculations were performed to obtain the MEP and the activation barrier for the diffusion of atomic hydrogen on Mg(0001) surface and into subsurface both with no carbon, with three sub-surface carbon atoms and with six sub-surface C atoms (see Fig.1a, Fig.1c and Fig.1d).…”

“…the dissociated atomic H will diffuse into subsurface through fcc channels. To date, the dissociative chemisorption of H 2 onto a clean magnesium surface has been reported by several groups [16][17][18][19]. We have recently carried out a preliminary investigation of the effect of incorporated carbon on the dissociative chemisorption of hydrogen [20].…”

“…Theoretically, ab initio DFT calculations have shown considerable predictive power for the analysis of catalytic mechanisms [14][15]. In the process of hydrogenation of Magnesium, hydrogen molecules first dissociate on Mg surface into adsorbed atoms [16][17] and then * To whom any correspondence should be addressed. the dissociated atomic H will diffuse into subsurface through fcc channels.…”

The role of V2O5 on the dehydrogenation and hydrogenation in magnesium hydride: An ab initio study

“…One of the possible reasons is that the hydrogen molecules do not readily dissociate on Mg surface. [4][5][6] Experimentally, many studies have been devoted to the catalytic effect on hydrogen adsorption of mixing transition metals or their oxides in small quantities into Mg hydride powder during ball milling. [7][8][9][10] The transition metals, such as Ti, Nb, V, etc.…”