A DFT study of H-dissolution into the bulk of a crystalline Ni(111) surface: a chemical identifier for the reaction kinetics

Abstract

In this study, we investigated the diffusion of H-atoms to the subsurface and their further diffusion into the bulk of a Ni(111) crystal by means of density functional theory calculations in the context of thermal and plasma-assisted catalysis. The H-atoms at the surface can originate from the dissociative adsorption of H 2 or CH 4 molecules, determining the surface H-coverage. When a threshold H-coverage is passed, corresponding to 1.00 ML for the crystalline Ni(111) surface, the surface-bound H-atoms start to diffuse to the subsurface. A similar threshold coverage is observed for the interstitial H-coverage. Once the interstitial sites are filled up with a coverage above 1.00 ML of H, dissolution of interstitial H-atoms to the layer below the interstitial sites will be initiated. Hence, by applying a high pressure or inducing a reactive plasma and high temperature, increasing the H-flux to the surface, a large amount of hydrogen can diffuse in a crystalline metal like Ni and can be absorbed. The formation of metal hydride may modify the entire reaction kinetics of the system. Equivalently, the H-atoms in the bulk can easily go back to the surface and release a large amount of heat. In a plasma process, H-atoms are formed in the plasma, and therefore the energy barrier for dissociative adsorption is dismissed, thus allowing achievement of the threshold coverage without applying a high pressure as in a thermal process. As a result, depending on the crystal plane and type of metal, a large number of H-atoms can be dissolved (absorbed) in the metal catalyst, explaining the high efficiency of plasma-assisted catalytic reactions. Here, the mechanism of H-dissolution is established as a chemical identifier for the investigation of the reaction kinetics of a chemical process.

Effect of plasma-induced surface charging on catalytic processes: application to CO2activation

“…Using DFT calculations 30 and molecular dynamics (MD) simulations, 31 it was confirmed that gas phase plasma activation of inert gasses such as CH4 leads to improved chemisorption, 31 whereas a high surface coverage of plasma-generated radicals can significantly modify the activity of the catalyst towards CO2 activation. 32,33 Of the many other possible plasma-surface interactions, perhaps the most intriguing is the ability of a plasma to modify the electronic structure of the catalyst through charging. All surfaces exposed to a gas discharge accumulate a negative charge due to the influx of plasmasupplied electrons, which is much larger than the influx of ions.…”

Dual-Route Hydrogenation of the Graphene/Ni Interface

“…The intensity of the C 1s components arising from hydrogenated graphene is transferred to C 1 , signaling the dissociation of C–H bonds. This demonstrates that the chemisorbed H atoms are released and indirectly proves that the intercalated H atoms get adsorbed on the Ni surface rather than binding to the bottom side of graphene. , Then a chemisorbed phase forms on the metal surface (the average H binding energy to Ni(111) varies in the range 2.9–1.4 eV, rapidly decreasing with increasing coverage). , …”

“…18,19 Then a chemisorbed phase forms on the metal surface (the average H binding energy to Ni(111) varies in the range 2.9−1.4 eV, rapidly decreasing with increasing coverage). 45,46 Determining how intercalation occurs at the atomic level is hard to assess at present, and it is beyond the aim of the present work. Penetration of Gr by hydrogen atoms can be confidently excluded since, in the absence of nanoscale openings, graphene is completely impermeable to thermal atoms and small molecules.…”

Dielectric Barrier Discharge Plasma-Assisted Catalytic CO2 Hydrogenation: Synergy of Catalyst and Plasma

“…Moreover, the dissociation of CO 2 was facilitated when they were activated by plasma to form vibrational and excited states, intrinsically accelerating the CO production in a lower energy barrier [82]. The improved CO 2 activation could be signaled by the production of CO 2 + , CO, CHO radicals, and C 2 species; and the last two species were mainly responsible for the high conversion to CH 4 with surface-bound H at low temperatures in Ni/Al 2 O 3 coupled with DBD plasma [83][84][85].…”