Dissociation of H2 on Mg(0001)

Bird, D. M.; Clarke, L. J.; Payne, Michael; Štich, Ivan

doi:10.1016/0009-2614(93)87239-y

Cited by 59 publications

(42 citation statements)

References 35 publications

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“…These compare well with previous theoretical results [25]. It is clear that there is a strong preference for the hollow sites, with a small preference for the fcc hollow site.…”

Section: B H2 Dissociation and H Diffusion On The Pure Mg And The Tisupporting

confidence: 92%

“…There are a few theoretical papers about the dissociation of molecular hydrogen on a pure Mg surface where the corresponding activation barrier has been effectively calculated. These investigations were based on a jellium model and potential energy surface(PES) calculations within density functional theory (DFT) with the local density approximation(LDA) or generalised gradient corrections (RPBE) [22,23,24,25,26].…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen dissociation and diffusion on Ni- and Ti-doped Mg(0001) surfaces

Pozzo

Alfè

Amieiro

et al. 2008

The Journal of Chemical Physics

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It is well known, both theoretically and experimentally, that alloying MgH2 with transition elements can significantly improve the thermodynamic and kinetic properties for H2 desorption, as well as the H2 intake by Mg bulk. Here we present a density functional theory investigation of hydrogen dissociation and surface diffusion over Ni-doped surface, and compare the findings to previously investigated Ti-doped Mg(0001) and pure Mg(0001) surfaces. Our results show that the energy barrier for hydrogen dissociation on the pure Mg(0001) surface is high, while it is small/null when Ni/Ti are added to the surface as dopants. We find that the binding energy of the two H atoms near the dissociation site is high on Ti, effectively impeding diffusion away from the Ti site. By contrast, we find that on Ni the energy barrier for diffusion is much reduced. Therefore, although both Ti and Ni promote H2 dissociation, only Ni appears to be a good catalyst for Mg hydrogenation, allowing diffusion away from the catalytic sites. Experimental results corroborate these theoretical findings, i.e. faster hydrogenation of the Ni doped Mg sample as opposed to the reference Mg or Ti doped Mg.

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“…These compare well with previous theoretical results [25]. It is clear that there is a strong preference for the hollow sites, with a small preference for the fcc hollow site.…”

Section: B H2 Dissociation and H Diffusion On The Pure Mg And The Tisupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Hydrogen dissociation and diffusion on Ni- and Ti-doped Mg(0001) surfaces

Pozzo

Alfè

Amieiro

et al. 2008

The Journal of Chemical Physics

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“…Following the reaction coordinate (see Fig. 3), the transition state for dissociation ͑TS 1 ͒ is found to be in the bridge site-in agreement with the findings of Bird et al, 5 but yielding a substantially higher activation energy of E 1 = 1.15 eV. A lower LDA barrier is expected, as a consequence of the LDA overbinding, 28 which is particularly pronounced in calculations, where bonds are broken and reformed for light atoms.…”

Section: H 2 Dissociation On Mg"0001…supporting

confidence: 86%

“…4 Bird et al have performed LDA calculations, determining the bridge site to be favored for H 2 dissociation, yielding a barrier of 0.4 eV for dissociation. 5 Experimentally, Plummer and Sprunger have used EELS and TDS to study the interaction between both atomic and molecular hydrogen and Mg, finding dissociation and adsorption to be activated; a strongly chemisorbed surface hydride state was also observed. 6,7 The diffusional properties of hydrogen in magnesium have been investigated by Renner and Grabke, who determined a diffusion constant of D = 4.0ϫ 10 −13 m 2 / s at 300 K. 8 Using neutron scattering, Töpler et al found H-diffusion in MgH 2 to be three orders of magnitude lower than in Mg (at 350 K), 9 and Spatz et al have determined the overall hydrogen diffusion coefficient for the Mg-to-MgH 2 -transition (including nucleation and growth) to be as low as DЈ = 1.1 ϫ 10 −20 m 2 / s using XPS.…”

Section: Introductionmentioning

confidence: 99%

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

2004

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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.

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“…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].…”

Section: Introductionmentioning

confidence: 99%