Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy
Hydrogen spillover is an elusive process, and its characterization, using experimental probes and ab initio modeling, poses a serious challenge. In this work, the nuclear quantum dynamics of hydrogen in a palladium-decorated cubic polymorph of tungsten oxide, Pd/cWO<sub>3</sub>, are char...
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MDPI AG
2023-07-01
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| Series: | Energies |
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| Online Access: | https://www.mdpi.com/1996-1073/16/14/5496 |
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| author | Erwin Lalik Stewart F. Parker Gavin Irvine Ivan da Silva Matthias Josef Gutmann Giovanni Romanelli Kacper Drużbicki Robert Kosydar Matthew Krzystyniak |
| author_facet | Erwin Lalik Stewart F. Parker Gavin Irvine Ivan da Silva Matthias Josef Gutmann Giovanni Romanelli Kacper Drużbicki Robert Kosydar Matthew Krzystyniak |
| author_sort | Erwin Lalik |
| collection | DOAJ |
| description | Hydrogen spillover is an elusive process, and its characterization, using experimental probes and ab initio modeling, poses a serious challenge. In this work, the nuclear quantum dynamics of hydrogen in a palladium-decorated cubic polymorph of tungsten oxide, Pd/cWO<sub>3</sub>, are characterized by the technique of neutron Compton scattering augmented by ab initio harmonic lattice modeling. The deeply penetrating nature of the neutron scattering process, the lack of spectroscopic selection rules, the inherent high sensitivity to hydrogen, the high energy and momentum resolution for hydrogen, and the mass selectivity of the technique render the neutron Compton scattering a very potent and unique tool for investigating the local dynamics of hydrogen species in bulk matrices. The total neutron Compton scattering response of hydrogen is described in terms of the hydrogen momentum distribution. The distribution is deconvoluted under the assumption of three pools of hydrogen with distinctly different nuclear quantum dynamical behavior: (i) hydrogen-terminated beta-palladium hydride, (ii) hydrogen in acid centers (OH+ groups) on the surface of the cubic phase of tungsten oxide, and (iii) quasi-free atomic hydrogen inside the saturated hydrogen bronze resulting from the spillover process. The ab initio modeling of lattice dynamics yields theoretical predictions for the values of the widths of proton momentum distributions in the first two hydrogen pools, which allows for obtaining the contribution and the width of the momentum distribution of the quasi-free atomic hydrogen resulting from the hydrogen spillover process. The analysis reveals that the local binding strength of the quasi-free hydrogen is characterized by the values of nuclear momentum distribution width, nuclear kinetic energy, and force constant of the underlying potential of the mean force close to those of free, unconstrained hydrogen atomic species in a gas of non-interacting particles described by the Maxwell–Boltzmann distribution. Moreover, this picture of the local dynamics of the quasi-free hydrogen is consistent with the proton polaron model of hydrogen-induced coloration of bulk hydrogenated WO<sub>3</sub>. |
| first_indexed | 2024-03-11T01:06:47Z |
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| id | doaj.art-6d27479b6edf45cb860105ca082fb4a3 |
| institution | Directory Open Access Journal |
| issn | 1996-1073 |
| language | English |
| last_indexed | 2024-03-11T01:06:47Z |
| publishDate | 2023-07-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Energies |
| spelling | doaj.art-6d27479b6edf45cb860105ca082fb4a32023-11-18T19:11:18ZengMDPI AGEnergies1996-10732023-07-011614549610.3390/en16145496Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron SpectroscopyErwin Lalik0Stewart F. Parker1Gavin Irvine2Ivan da Silva3Matthias Josef Gutmann4Giovanni Romanelli5Kacper Drużbicki6Robert Kosydar7Matthew Krzystyniak8Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Cracow, PolandISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UKSchool of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UKISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UKISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UKDipartimento di Fisica and NAST Centre, Università degli Studi di Roma Tor Vergata, 00133 Rome, ItalyMaterials Physics Center, CSIC-UPV/EHU, Paseo de Manuel Lardizabal 5, 20018 Donostia-San Sebastian, SpainJerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Cracow, PolandISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UKHydrogen spillover is an elusive process, and its characterization, using experimental probes and ab initio modeling, poses a serious challenge. In this work, the nuclear quantum dynamics of hydrogen in a palladium-decorated cubic polymorph of tungsten oxide, Pd/cWO<sub>3</sub>, are characterized by the technique of neutron Compton scattering augmented by ab initio harmonic lattice modeling. The deeply penetrating nature of the neutron scattering process, the lack of spectroscopic selection rules, the inherent high sensitivity to hydrogen, the high energy and momentum resolution for hydrogen, and the mass selectivity of the technique render the neutron Compton scattering a very potent and unique tool for investigating the local dynamics of hydrogen species in bulk matrices. The total neutron Compton scattering response of hydrogen is described in terms of the hydrogen momentum distribution. The distribution is deconvoluted under the assumption of three pools of hydrogen with distinctly different nuclear quantum dynamical behavior: (i) hydrogen-terminated beta-palladium hydride, (ii) hydrogen in acid centers (OH+ groups) on the surface of the cubic phase of tungsten oxide, and (iii) quasi-free atomic hydrogen inside the saturated hydrogen bronze resulting from the spillover process. The ab initio modeling of lattice dynamics yields theoretical predictions for the values of the widths of proton momentum distributions in the first two hydrogen pools, which allows for obtaining the contribution and the width of the momentum distribution of the quasi-free atomic hydrogen resulting from the hydrogen spillover process. The analysis reveals that the local binding strength of the quasi-free hydrogen is characterized by the values of nuclear momentum distribution width, nuclear kinetic energy, and force constant of the underlying potential of the mean force close to those of free, unconstrained hydrogen atomic species in a gas of non-interacting particles described by the Maxwell–Boltzmann distribution. Moreover, this picture of the local dynamics of the quasi-free hydrogen is consistent with the proton polaron model of hydrogen-induced coloration of bulk hydrogenated WO<sub>3</sub>.https://www.mdpi.com/1996-1073/16/14/5496heterogeneous catalysishydrogen bronzeshydrogen spilloverneutron Compton scatteringnuclear quantum effects |
| spellingShingle | Erwin Lalik Stewart F. Parker Gavin Irvine Ivan da Silva Matthias Josef Gutmann Giovanni Romanelli Kacper Drużbicki Robert Kosydar Matthew Krzystyniak Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy Energies heterogeneous catalysis hydrogen bronzes hydrogen spillover neutron Compton scattering nuclear quantum effects |
| title | Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy |
| title_full | Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy |
| title_fullStr | Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy |
| title_full_unstemmed | Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy |
| title_short | Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy |
| title_sort | hydrogen spillover in tungsten oxide bronzes as observed by broadband neutron spectroscopy |
| topic | heterogeneous catalysis hydrogen bronzes hydrogen spillover neutron Compton scattering nuclear quantum effects |
| url | https://www.mdpi.com/1996-1073/16/14/5496 |
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