Operando methodology: combination of in situ spectroscopy and simultaneous activity measurements under catalytic reaction conditions

Hydrogen adsorption, absorption and diffusion on and in transition metal surfaces: A DFT study

Periodic, self-consistent DFT-GGA calculations are used to study the thermochemical properties of both surface and subsurface atomic hydrogen on a variety of pure metals and near-surface alloys (NSAs). For surface hydrogen on pure metals, calculated site preferences, adsorption geometries, vibrational frequencies, and binding energies are reported and are found to be in good agreement with available experimental data. On NSAs, defined as alloys wherein a solute is present near the surface of a host metal in a composition different from the bulk composition, surface hydrogen generally binds more weakly than it binds to the pure-metal components composing the alloys. Some of the NSAs even possess the unusual property of binding hydrogen as weakly as the noble metals while, at the same time, dissociating H2 much more easily. On both NSAs and pure metals, formation of surface hydrogen is generally exothermic with respect to H2(g). In contrast, formation of subsurface hydrogen is typically endothermic with res...

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Surface and subsurface hydrogen: adsorption properties on transition metals and near-surface alloys.

Conversion of the greenhouse gas carbon dioxide (CO2) to value-added products is an important challenge for sustainable energy research, and nanomaterials offer a broad class of heterogeneous catalysts for such transformations. Here we report a molecular surface functionalization approach to tuning gold nanoparticle (Au NP) electrocatalysts for reduction of CO2 to CO. The N-heterocyclic (NHC) carbene-functionalized Au NP catalyst exhibits improved faradaic efficiency (FE = 83%) for reduction of CO2 to CO in water at neutral pH at an overpotential of 0.46 V with a 7.6-fold increase in current density compared to that of the parent Au NP (FE = 53%). Tafel plots of the NHC carbene-functionalized Au NP (72 mV/decade) vs parent Au NP (138 mV/decade) systems further show that the molecular ligand influences mechanistic pathways for CO2 reduction. The results establish molecular surface functionalization as a complementary approach to size, shape, composition, and defect control for nanoparticle catalyst design.

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A Molecular Surface Functionalization Approach to Tuning Nanoparticle Electrocatalysts for Carbon Dioxide Reduction.

First-principles study of the adsorption of atomic H on Ni (111), (100) and (110)

We report that hydrogen can induce surface reconstructions by adsorption even on close-packed substrates. New low-energy electron-diffraction analyses for H/Ni(111) and H/Fe(110) show that consideration of reconstruction is essential for a convincing experiment-theory fit as well as for reliable determination of the adsorption site. There are two different types of reconstruction: Hydrogen pulls nickel atoms out of the surface but pushes iron atoms towards the bulk. These findings are mirrored by a different sign of work-function change for both systems and demonstrate the correlation between geometric and electronic structure.

Hydrogen-induced restructuring of close-packed metal surfaces: H/Ni(111) and H/Fe(110).

Structure determination of p4g Ni(100)-(2 × 2)C by LEED

Low-temperature p2mg (2 × 1) structure of ultrathin epitaxial films Fe/Cu(100)

The clean and H-induced reconstruction of W(100) studied by LEED at slanting primary bean incidence

A LEED structure analysis is performed for the W(100) c(2*2) surface reconstruction. Models with pure vertical displacements of the surface atoms can be clearly ruled out while others with predominant lateral displacements in the (11) and (01) directions result in a very good agreement with the experimental curves. However, a clear discrimination between these models is prevented by the insensitivity of normal incidence spectra to the direction of atomic displacements parallel to the surface. A minimum Pendry r-factor of r=0.26 is achieved for a refined model suggested by Debe and King (1979) with a multilayer relaxation (first inter-layer spacing d12=witht1.47 AA second inter-layer spacing d23=1.60 AA, and a reconstruction in the first and second layer with lateral displacements in the (11) direction (first layer: 0.24 AA; second layer: 0.02 AA).

H. Landskron

Papers

Hydrogen-induced restructuring of close-packed metal surfaces: H/Ni(111) and H/Fe(110).

Structure determination of p4g Ni(100)-(2 × 2)C by LEED

Low-temperature p2mg (2 × 1) structure of ultrathin epitaxial films Fe/Cu(100)

The clean and H-induced reconstruction of W(100) studied by LEED at slanting primary bean incidence

LEED intensity analysis of the clean W(100) c(2×2) surface reconstruction