Kinetic Monte Carlo Study of Competing Hydrogen Pathways into Connected (100), (110), and (111) Ni Surfaces

Haug, Kenneth; Raibeck, Gretel

doi:10.1021/jp030596n

“…This information, when combined with insights from recent work showing that large stretched areas are induced in crystal surfaces by dislocations that originate in the bulk, [8] implies that nickel crystals with such defects will absorb hydrogen more readily than perfect Ni(111) surfaces. This mechanism for strain-mediated formation of subsurface hydrogen around defects, possibly combined with previous proposals for subsurface H formation by grain-boundary diffusion and/or direct hydrogen penetration through steps and kinks, [11,30] could explain the observed higher solubility of hydrogen in polycrystalline, as opposed to single-crystal, nickel samples. [31] In turn, we suggest that, if subsurface species play a special role in catalytic surface chemistry, that role might be more pronounced on real catalytic particles, where defect density is much higher than on single crystal surfaces.…”

Section: Methodssupporting

confidence: 68%

Strain‐Induced Formation of Subsurface Species in Transition Metals

Greeley

¹

,

Krekelberg

²

,

Mavrikakis

³

2004

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Surface strain has recently been shown to have a significant effect on the reactivity of transition-metal surfaces, [1] and numerous examples of strain effects on both the thermochemistry and kinetics of surface reactions have been identified. [2][3][4][5][6][7] Several of these studies focused on strain induced by epitaxial metal overlayers, but recently it has been demonstrated that strain from another source, namely, dislocations that intersect crystal surfaces, likewise causes significant changes in surface reactivity. [8] This suggests that a careful study on the effect of strain on catalytic processes might yield substantial insights into the effect of defects on these processes. Defects, in turn, have been shown to dominate the reactivity of certain surface reactions. [9] In particular, an analysis of the manner in which strain influences the population of subsurface species in transition metals could contribute to an understanding of the more general problem of how dislocation-induced surface defects mediate the transfer of adsorbates to subsurface regions. Such an analysis could permit a comparison between the behavior of subsurface species on single-crystal and polycrystalline metals, [10,11] and it could have broad application to a number of technologically important problems, including the catalytic reactivity of subsurface oxygen and carbon in connection with corrosion, oxidation, or carbonylation processes, [12,13] subsurface hydrogen reactivity for hydrogenation and hydrogenolysis reactions, [14][15][16][17][18][19] hydrogen storage in and embrittlement of metals, [11,20,21] and the purification of hydrogen fuel streams with Pd-alloy membranes. [22,23] Here we analyze the effect of strain on the creation of subsurface species in metals by focusing on the hydrogen/ nickel system and using periodic, self-consistent density functional theory (DFT) calculations. As recent atomically resolved STM images of surface defects on Ru(0001) showed regions with lattice stretching of up to 10 % in the immediate vicinity of these defects, [8] we focused our studies on Ni(111) slabs with 3 and 10 % expansive strain. We show that, while very high H 2 pressures are required to produce subsurface hydrogen on perfect, unstretched Ni(111) surfaces, [24] only modest pressures (on the order of tens of bar) are required for subsurface hydrogen to form on the stretched Ni surfaces that might exist in the vicinity of defects. We also demonstrate that strain qualitatively changes both the site preferences of subsurface hydrogen and the character of the stable surface and subsurface phases of the H/Ni(111) system. We discuss these results in the context of defect-mediated penetration of hydrogen into subsurface regions of both single-crystal and polycrystalline nickel catalysts, and we comment on the implications of the results for other processes involving various subsurface species in transition metals.A summary of the low-coverage (q = 0.25 ML (ML = monolayer), corresponding to one H atom per four surface Ni atoms) data fo...

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“…This information, when combined with insights from recent work showing that large stretched areas are induced in crystal surfaces by dislocations that originate in the bulk,8 implies that nickel crystals with such defects will absorb hydrogen more readily than perfect Ni(111) surfaces. This mechanism for strain‐mediated formation of subsurface hydrogen around defects, possibly combined with previous proposals for subsurface H formation by grain‐boundary diffusion and/or direct hydrogen penetration through steps and kinks,11, 30 could explain the observed higher solubility of hydrogen in polycrystalline, as opposed to single‐crystal, nickel samples 31. In turn, we suggest that, if subsurface species play a special role in catalytic surface chemistry, that role might be more pronounced on real catalytic particles, where defect density is much higher than on single crystal surfaces.…”

Section: Binding Energies Beh For Surface and Subsurface Hydrogen On supporting

confidence: 76%

Strain‐Induced Formation of Subsurface Species in Transition Metals

Greeley

¹

,

Krekelberg

²

,

Mavrakis

³

2004

View full text Add to dashboard Cite

Surface strain has recently been shown to have a significant effect on the reactivity of transition-metal surfaces, [1] and numerous examples of strain effects on both the thermochemistry and kinetics of surface reactions have been identified. [2][3][4][5][6][7] Several of these studies focused on strain induced by epitaxial metal overlayers, but recently it has been demonstrated that strain from another source, namely, dislocations that intersect crystal surfaces, likewise causes significant changes in surface reactivity. [8] This suggests that a careful study on the effect of strain on catalytic processes might yield substantial insights into the effect of defects on these processes. Defects, in turn, have been shown to dominate the reactivity of certain surface reactions. [9] In particular, an analysis of the manner in which strain influences the population of subsurface species in transition metals could contribute to an understanding of the more general problem of how dislocation-induced surface defects mediate the transfer of adsorbates to subsurface regions. Such an analysis could permit a comparison between the behavior of subsurface species on single-crystal and polycrystalline metals, [10,11] and it could have broad application to a number of technologically important problems, including the catalytic reactivity of subsurface oxygen and carbon in connection with corrosion, oxidation, or carbonylation processes, [12,13] subsurface hydrogen reactivity for hydrogenation and hydrogenolysis reactions, [14][15][16][17][18][19] hydrogen storage in and embrittlement of metals, [11,20,21] and the purification of hydrogen fuel streams with Pd-alloy membranes. [22,23] Here we analyze the effect of strain on the creation of subsurface species in metals by focusing on the hydrogen/ nickel system and using periodic, self-consistent density functional theory (DFT) calculations. As recent atomically resolved STM images of surface defects on Ru(0001) showed regions with lattice stretching of up to 10 % in the immediate vicinity of these defects, [8] we focused our studies on Ni(111) slabs with 3 and 10 % expansive strain. We show that, while very high H 2 pressures are required to produce subsurface hydrogen on perfect, unstretched Ni(111) surfaces, [24] only modest pressures (on the order of tens of bar) are required for subsurface hydrogen to form on the stretched Ni surfaces that might exist in the vicinity of defects. We also demonstrate that strain qualitatively changes both the site preferences of subsurface hydrogen and the character of the stable surface and subsurface phases of the H/Ni(111) system. We discuss these results in the context of defect-mediated penetration of hydrogen into subsurface regions of both single-crystal and polycrystalline nickel catalysts, and we comment on the implications of the results for other processes involving various subsurface species in transition metals.A summary of the low-coverage (q = 0.25 ML (ML = monolayer), corresponding to one H atom per four surface Ni atoms) data fo...

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“…2; see also Table 1) is to create a complete catalog of all possible processes along with their transition probabilities. This key input to any KMC simulation can be extracted from smaller length and time scale simulation tools, such as density functional theory (DFT) [18,[99][100][101][102] (these are often termed first principles KMC simulations), transition state identification methods, transition state theory (TST) [103,104], and MD [3,4,61,105,106] typically via a bottom-up approach (information passage from small to large scales) [36,[107][108][109][110]. Significant work in this area to address the computational requirements of DFT and MD and the approximations involved, e.g., in TST, has led to the development of a whole new research area.…”

Section: Input To a Kmc Simulationmentioning

confidence: 99%

An overview of spatial microscopic and accelerated kinetic Monte Carlo methods

Chatterjee

¹

,

Vlachos

²

2007

J Computer-Aided Mater Des

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The microscopic spatial kinetic Monte Carlo (KMC) method has been employed extensively in materials modeling. In this review paper, we focus on different traditional and multiscale KMC algorithms, challenges associated with their implementation, and methods developed to overcome these challenges. In the first part of the paper, we compare the implementation and computational cost of the null-event and rejection-free microscopic KMC algorithms. A firmer and more general foundation of the null-event KMC algorithm is presented. Statistical equivalence between the null-event and rejection-free KMC algorithms is also demonstrated. Implementation and efficiency of various search and update algorithms, which are at the heart of all spatial KMC simulations, are outlined and compared via numerical examples. In the second half of the paper, we review various spatial and temporal multiscale KMC methods, namely, the coarse-grained Monte Carlo (CGMC), the stochastic singular perturbation approximation, and the τ -leap methods, introduced recently to overcome the disparity of length and time scales and the one-at-a time execution of events. The concepts of the CGMC and the τ -leap methods, stochastic closures, multigrid methods, error associated with coarse-graining, a posteriori error estimates for generating spatially adaptive coarse-grained lattices, and computational speed-up upon coarse-graining are illustrated through simple examples from crystal growth, defect dynamics, adsorption-desorption, surface diffusion, and phase transitions.

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Kinetic Monte Carlo Study of Competing Hydrogen Pathways into Connected (100), (110), and (111) Ni Surfaces

Cited by 8 publications

References 57 publications

Strain‐Induced Formation of Subsurface Species in Transition Metals

Strain‐Induced Formation of Subsurface Species in Transition Metals

Strain‐Induced Formation of Subsurface Species in Transition Metals

An overview of spatial microscopic and accelerated kinetic Monte Carlo methods

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