Hydrogen Spillover in Tungsten Oxide Bronzes as Observed by Broadband Neutron Spectroscopy

Erwin Lalik, Stewart F. Parker, Gavin Irvine, Ivan da Silva, Matthias Josef Gutmann, Giovanni Romanelli, Kacper Drużbicki, Robert Kosydar and Matthew Krzystyniak ()
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Erwin Lalik: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Cracow, Poland
Stewart F. Parker: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
Gavin Irvine: School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK
Ivan da Silva: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
Matthias Josef Gutmann: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
Giovanni Romanelli: Dipartimento di Fisica and NAST Centre, Università degli Studi di Roma Tor Vergata, 00133 Rome, Italy
Kacper Drużbicki: Materials Physics Center, CSIC-UPV/EHU, Paseo de Manuel Lardizabal 5, 20018 Donostia-San Sebastian, Spain
Robert Kosydar: Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Cracow, Poland
Matthew Krzystyniak: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK

Energies, 2023, vol. 16, issue 14, 1-20

Abstract: 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 3 , 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 3 .

Keywords: heterogeneous catalysis; hydrogen bronzes; hydrogen spillover; neutron Compton scattering; nuclear quantum effects (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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