Unravelling the hydrogen absorption process in Pd overlayers on a Au(111) surface

Quaino, Paola; Nazmutdinov, Renat R.; Peiretti, Leonardo Federico; Santos, Elizabeth

doi:10.1039/c5cp06443k

Cited by 10 publications

(10 citation statements)

References 60 publications

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“…This effect can be also explained by the density of state (DOS) changes in Au and Pd alloy. Quaino et al showed by density functional theory (DFT) calculations for Au(111) surface on Pd, that the Fermi level of an alloy was lower in energy due to the Au:Pd bond formation [54]. We have also confirmed this prediction by DFT calculations in Fig.…”

Section: Surface Adsorption / Desorption On Au-pd Alloysupporting

confidence: 78%

Optical readout of hydrogen storage in films of Au and Pd

et al. 2017

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For hydrogen sensor and storage applications, films of Au and Pd were (i) cosputtered at different rates or (ii) deposited in a sequential layer-by-layer fashion on a cover glass. Peculiarities of hydrogen uptake and release were optically monitored using 1.3 µm wavelength light. Increase of optical transmission was observed for hydrogenated Pd-rich films of 10-30 nm thickness. Up to a three times slower hydrogen release took place as compared with the hydrogen uptake. Compositional ratio of Au:Pd and thermal treatment of films provided control over the optical extinction changes and hydrogen uptake/release time constants. Higher uptake and release rates were observed in the annealed Au:Pd films as compared to those deposited at room temperature and were faster for the Au-richer films. Three main parameters relevant for sensors: sensitivity, selectivity, stability (reproducibility) are discussed together with the hydrogenation mechanism in Au:Pd alloys.

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Section: Surface Adsorption / Desorption On Au-pd Alloysupporting

confidence: 78%

Optical readout of hydrogen storage in films of Au and Pd

et al. 2017

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“…This approximation is supported by previous DFT studies. 44 The local densities of states (LDOS) projected on the dband for the various structures investigated are shown in Figure 8. The d-band shows an upward shift with a decreasing shell thickness, with a slight peak narrowing.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Strain Effects on the Oxidation of CO and HCOOH on Au–Pd Core–Shell Nanoparticles

et al. 2017

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The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermediate species only in the case of CS1. This observation allowed us to conclude that the higher activity of CS10 toward this reaction is due to a fast HCOOads oxidation step, probably involving OHads, to generate CO2. Density functional theory calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameter contributing to the change in mechanism is the effective lattice strain.

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“…It might also be possible to have hcp + fcc 3f sites occupied as in the Pd 4 ensemble shown in Scheme 2p, similar to the structure proposed for the adsorption of hydrogen atoms on adjacent 3-fold hollow sites. 60,61 However, the repulsion between two adjacent adsorbed CO molecules suggests that this structure would be energetically unfavorable.…”

Section: C Site Distribution As a Function Of Alloy Compositionmentioning

confidence: 99%

Combining IR Spectroscopy and Monte Carlo Simulations to Identify CO Adsorption Sites on Bimetallic Alloys

2019

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The atomic distribution on the surface of alloys dictates the nature of the ensembles available as possible active sites during catalytic reactions. In the present work, an infrared spectroscopic study of carbon monoxide adsorption on the surface of AuPd/Pd(111) alloys, combined with Monte Carlo simulations of the surface and bulk atomic distribution, identifies the correct distribution of available surface adsorption sites. For gold coverages >0.9 monolayers (ML), CO adsorbs weakly on top of Au atoms and with higher adsorption energy on top of Pd atoms (CO top ), distributed mostly as monomers on the surface. For θ Au = 0.8−0.4 ML, Pd− CO top is the predominant species, even though several other sites with multiple coordination are available. The simulations show no perfect ordering of the surface but a slight tendency to form lines of Pd atoms, thus favoring the appearance of bridge but not 3-fold hollow sites. Using 13 CO: 12 CO isotopic mixtures, the frequency shifts due to chemical and intermolecular coupling effects has been determined for the CO top IR signal. These effects mostly cancel each other out, so that only small frequency shifts are seen, implying the presence of significant electronic/ligand effects. At θ Au < 0.5 ML, hollow sites are experimentally observed in agreement to the simulated model surfaces. Their IR absorption bands are tentatively distinguished as fcc and hcp hollow sites by correlating with the simulated distribution of Au and Pd atoms on subsurface sites, where for θ Au < 0.5 ML an enrichment by Au atoms is seen in the near-surface region.

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Unravelling the hydrogen absorption process in Pd overlayers on a Au(111) surface

Cited by 10 publications

References 60 publications

Optical readout of hydrogen storage in films of Au and Pd

Optical readout of hydrogen storage in films of Au and Pd

Strain Effects on the Oxidation of CO and HCOOH on Au–Pd Core–Shell Nanoparticles

Combining IR Spectroscopy and Monte Carlo Simulations to Identify CO Adsorption Sites on Bimetallic Alloys

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