Quasi‐One‐Dimensional Behaviour of Hydrogen in H0.35MoO3 and H0.33WO3 as Revealed by Proton NMR

Ritter, Cl.; Müller‐Warmuth, W.; Spiess, Hans Wolfgang; Schöllhorn, R.

doi:10.1002/bbpc.198200047

Cited by 35 publications

(33 citation statements)

References 19 publications

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“…Except for LDA at x = 0.25, the O a -a position is energetically the most favorable site for H regardless of the exchange-correlation functional and the H content. This is consistent with experiments for x < 0.25 [16][17][18][19], where H resides along the zig-zag chains of the O a sites in the intrabilayer region.…”

Section: H Adsorption Energy In Bulk Moo3supporting

confidence: 91%

“…The most significant inconsistency regards the O site claimed to be the energetically most favorable for H to be adsorbed. Some studies [29,35,36] reported that the O a site is energetically more favorable than the other O sites, consistent with powder neutron diffraction [16,17] and nuclear magnetic resonance [18,19] for bulk H x MoO 3 with x ≤ 0.5. Other ab initio reports [23,24,26,28], in contrast, claimed that the O t site is more favorable than the O a site.…”

Section: Review On Previous Ab Initio Studiessupporting

confidence: 55%

“…In experiments, these issues have been addressed by considering hydrogen bronze, i.e., H x MoO 3 with 0 < x ≤ 2. For a relatively low H content of x ≤ 0.5, powder neutron diffraction [16,17] and nuclear magnetic resonance [18,19] showed that H is bound to the asymmetric oxygen (O a ) sites and resides in the intrabilayer region. For higher H contents of 1.55 < x ≤ 2, pow- * yuji.ikeda@imw.uni-stuttgart.de der neutron diffraction [20,21] showed that H is bound to the terminal oxygen (O t ) sites and resides in the interbilayer region.…”

Section: Introduction 1motivationmentioning

confidence: 99%

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Comprehensive understanding of H adsorption on MoO3 from systematic ab initio simulations

Ikeda,

Estes,

Grabowski

2021

Preprint

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During many of its applications (especially as a catalyst support material), MoO3 acts as a medium for hydrogen storage via hydrogen spillover (H atom donation from proton and electron sources to a support), for which the energetics of H atoms on MoO3 are of importance. Despite the seeming simplicity of hydrogen spillover, previously reported ab initio results for the H adsorption on MoO3 contradict both experimental work and other ab initio results. In the present study, we resolve these discrepancies and provide a comprehensive ab initio understanding of H adsorption for MoO3 in the bulk and on the surface. To this end, we systematically investigate various exchange-correlation functionals and various H concentrations, and we carefully track the various relevant H positions. For a dilute H concentration, the asymmetric oxygen site (Oa) is found to be energetically the most favorable. With increasing H content, the difference of the H adsorption energies between the terminal (Ot) and the Oa sites becomes smaller. Previous contradictions are ascribed mostly to the disregard of the H position along the Oa-Oa zig-zag chains in the intrabilayer region. Using the modern non-empirical strongly-constrained and appropriately-normed (SCAN) meta-generalized gradient approximation (GGA), the dilute-limit H adsorption energies are obtained as −2.89 eV/(H atom) and −2.97 eV/(H atom) in the bulk and on the surface, respectively, and the activation energy of H diffusion between the Oa sites as 0.11-0.15 eV/(H atom), consistent with previous experiments.

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Section: H Adsorption Energy In Bulk Moo3supporting

confidence: 91%

Section: Review On Previous Ab Initio Studiessupporting

confidence: 55%

Section: Introduction 1motivationmentioning

confidence: 99%

See 1 more Smart Citation

Comprehensive understanding of H adsorption on MoO3 from systematic ab initio simulations

Ikeda,

Estes,

Grabowski

2021

Preprint

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“…The O2 sites (with an adsorption energy of 3.58 eV) are the most energetically favorable for hydrogen adsorption compared with the O1 (3.06 eV) and O3 (1.13 eV) sites (Supplementary Table 4). In addition, hydrogens are alternately located along the zig-zag chains of intralayer oxygen atoms ([001] direction) within MoO 6 octahedra 31 . By comparing the calculated thermodynamic stabilities for hydrogen diffusion along the [203] direction and along the [001] direction, we find the former to be slightly more energetically favorable (15 meV), possibly because of the cationic repulsion (Supplementary Fig.…”

Section: Analysis Of Intermediate States During Hydrogenationmentioning

confidence: 99%

Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation

Yin

et al. 2020

Nat Commun

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Phonon polaritons (PhPs) have attracted significant interest in the nano-optics communities because of their nanoscale confinement and long lifetimes. Although PhP modification by changing the local dielectric environment has been reported, controlled manipulation of PhPs by direct modification of the polaritonic material itself has remained elusive. Here, chemical switching of PhPs in α-MoO 3 is achieved by engineering the α-MoO 3 crystal through hydrogen intercalation. The intercalation process is non-volatile and recoverable, allowing reversible switching of PhPs while maintaining the long lifetimes. Precise control of the intercalation parameters enables analysis of the intermediate states, in which the needle-like hydrogenated nanostructures functioning as in-plane antennas effectively reflect and launch PhPs and form well-aligned cavities. We further achieve spatially controlled switching of PhPs in selective regions, leading to in-plane heterostructures with various geometries. The intercalation strategy introduced here opens a relatively non-destructive avenue connecting infrared nanophotonics, reconfigurable flat metasurfaces and van der Waals crystals.

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“…[42][43][44][45][46][47][48][49] Sheik, Saleem and Aruldhas 50 observed very intense IR bands at 3215, 3185, 3172, and 3155 cm -1 in molybdenum hydrates. The position of the high-frequency band observed by these authors is in good agreement with the absorption at 3220 cm -1 detected in this experiment.…”

Section: R )mentioning

confidence: 99%

Mechanically Activated MoO₃. 5. Redox Behavior

et al. 1996

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Mechanical activation leads to a variety of defects in MoO3. The behavior of paramagnetic defects in unmilled MoO3 and in MoO3 mechanically activated in a planetary mill for 600 min was investigated by ESR spectroscopy. MoO3 milled for 600 min, and unmilled MoO3 though in a smaller concentration, contain Mo 5+ ions. N2 treatment at elevated temperatures increases the Mo 5+ concentration in the samples due to oxygen loss. Both MoO3 samples contain octahedrally coordinated Mo 5+ species prior to any treatment which interact with a proton in close proximity. An additional signal is observed in both samples that is characteristic of F centers. An inverse Curie-Weiss behavior between 90 and 300 K indicates the pairing of electrons at lower temperatures. Fivefold coordinated Mo 5+ species in distorted, square-pyramidal symmetry are generated in the bulk of unmilled MoO3 during N2 flushing at 523 and 623 K. MoO3 milled for 600 min contains, besides 6-fold coordinated Mo 5+ in C2v symmetry, a second Mo 5+ species in almost C4v symmetry. The Mo-O distances in the equatorial plane are shortened and these Mo 5+ centers are assigned to a precursor structure of crystallographic shear planes. Besides 6-fold coordinated Mo 5+ , tetrahedrally coordinated Mo 5+ centers are also generated, if milled MoO3 is treated in N2 at 623 or 673 K which are assigned to the Mo sites on shear defects protruding from the surface. The total intensity of the Mo 5+ signals follows the Curie-Weiss law between 90 and 200 K. Above 200 K a deviation from linearity is observed. Hence, a considerable part of the Mo 5+ centers does not contribute to the signal intensity at higher temperatures. In situ Raman spectroscopy of mechanically activated MoO3 revealed the formation of some nonstoichiometric MoO3-x after thermal treatment at 673 K in N2 for 1 h. In addition, diffuse reflectance infrared spectroscopy (DRIFTS) was used to characterize the stability of OH groups on the surface of MoO3 and in the bulk of the milled sample. The OH species located in the bulk of MoO3 was found to be stable even at 673 K under flowing N2.

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Quasi‐One‐Dimensional Behaviour of Hydrogen in H_0.35MoO₃ and H_0.33WO₃ as Revealed by Proton NMR

Cited by 35 publications

References 19 publications

Comprehensive understanding of H adsorption on MoO3 from systematic ab initio simulations

Comprehensive understanding of H adsorption on MoO3 from systematic ab initio simulations

Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation

Mechanically Activated MoO₃. 5. Redox Behavior

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Quasi‐One‐Dimensional Behaviour of Hydrogen in H0.35MoO3 and H0.33WO3 as Revealed by Proton NMR

Cited by 35 publications

References 19 publications

Comprehensive understanding of H adsorption on MoO3 from systematic ab initio simulations

Comprehensive understanding of H adsorption on MoO3 from systematic ab initio simulations

Chemical switching of low-loss phonon polaritons in α-MoO3 by hydrogen intercalation

Mechanically Activated MoO3. 5. Redox Behavior

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Quasi‐One‐Dimensional Behaviour of Hydrogen in H_0.35MoO₃ and H_0.33WO₃ as Revealed by Proton NMR

Mechanically Activated MoO₃. 5. Redox Behavior