H Resurface and Hot H Promoted H₂ Recombination on Ni(111): Effects of Arrangement, Surface Coverage, and Lattice Motion

Abstract

Subsurface H can affect catalytic reactivity and selectivity. H resurface and H2 recombination with a subsurface H on Ni(111) were investigated by the quantum instanton method, and the arrangement, surface coverage, lattice motion, and hot H effects were explored. The arrangement effect of a surface H and a subsurface H varied the H resurfacing rate constant by 57 times at 300 K. From the clean Ni(111) to two H adsorbed Ni(111), the increase of surface coverage suppressed the H resurfacing rate constant by four orders of magnitude at 300 K, whereas it increased the H penetration rate constant by about 10 times. The lattice motion effect was extremely remarkable for H resurface, H penetration, and direct H2 recombination, which enhanced the corresponding rate constants by about 10, 14, and 9 orders of magnitude, respectively, at 300 K. The hot resurfacing H could speed up H2 recombination by 140 times at 300 K. For the H2 recombination of a surface H and a subsurface H, the two-step process was much faster than the direct process. In the two-step process, H resurface was the rate-limiting step at extremely low temperatures due to the frozen lattice, while the recombination of two surface H atoms became the rate-limiting step as the lattice was relaxed with increasing temperature.

Interplay among Hydrogen Chemisorption, Intercalation, and Bulk Diffusion at the Graphene-Covered Ni(111) Crystal

“…Concerning the stability of the subsurface H atoms, for the Ni(111) surface dosed at low temperature, it has been demonstrated that they resurface with several tenths of electronvolt excess energy, 7,9,11 recombine with surface atoms, and desorb between 180 and 215 K as H 2 . 10,42 These experimental results have motivated many theoretical stud- [7][8][9]11,15,17,40,41,43 which found that the heights of the diffusion barriers from subsurface to surface sites depend on lattice relaxation, surface and subsurface H coverages, and also, at low temperature, tunneling effects and correlated motion of the hydrogen and nickel atoms. Anyhow, there is a general agreement on the fact that a high occupation number of surface sites decreases the resurfacing rate.…”

“…4 θ Ni values are in principle possible when dosing H atoms, and in this respect we find that for the Ni(111) surface where all fcc and hcp sites are hydrogenated (θ Ni = 2 ML Ni ), the adsorption energy per H atom is −2.29 eV. However, for the bare Ni(111) exposed to the H atom flux, experimental results 6,10,12 and DFT calculations 15,17,40,41 indicate that at high surface coverage H atoms tend to penetrate subsurface, where they are kinetically trapped at metastable octahedral and tetrahedral sites. Moreover, subsurface H atoms can also easily diffuse deeper in the bulk.…”

“…In this respect nickel, besides featuring a high catalytic activity, possesses a strong sorption ability which makes it elective materials for solid-state hydrogen storage systems, also in the form of Ni-based compounds and alloys. Therefore, the hydrogenation of nickel crystals, which has been extensively investigated throughout the 1990s and early 2000s, − is recently motivating new experimental and theoretical studies. − Concerning hydrogen loading in the Ni bulk, it is known that it requires the exposure to H 2 molecules at high pressure and high temperature, up to the formation of the metal hydride. Alternatively, hyperthermal H atoms, even at low temperatures, can penetrate the Ni surface and populate the Ni bulk.…”

Direct and steady state rate constants of C2H6 + X (X = H, Cl, OH): influence of the van der Waals well

“…54 It has successfully predicted the rate constants and kinetic isotope effects for gas phase 55–57 and gas-surface reactions. 58–60…”

Electrocatalytic hydrogenation of indigo by NiMoS: energy saving and conversion improving

“…15 Moreover, non-metallic atoms such as N, P, and S facilitate electron redistribution and optimize the electronic structure, enhancing the adsorption of atomic hydrogen and organic molecules on the surface. 16 Previous literature indicates that Ni is effective in water electrolysis, 17 Mo is effective in hydrogen atom adsorption, 18 and the introduction of sulfur can improve reaction activity by altering the d-band position of transition metal elements. 19 Considering these factors, NiMoS should offer energy savings for water splitting and improved conversion rates for ECH.…”