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Hydrogen spillover in tungsten oxide bronzes as observed by broadband neutron spectroscopy

Vendredi 5 avril 11:00 - Duree : 1 heure
Lieu : ILL 4, Seminar Room, 71 avenue des Martyrs - Grenoble

Orateur : Matthew KRZYSTYNIAK (ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom)

General ILL Seminar - College 7 :

Résumé :

Hydrogen spillover is an elusive process, and its characterization, by means of experimental probes and ab initio modelling, poses a serious challenge. In this work, the nuclear quantum dynamics of hydrogen in a palladium-decorated cubic polymorph of tungsten oxide, Pd/cWO3, are characterized by the unique technique of neutron Compton scattering augmented by ab initio harmonic lattice modelling. The total neutron Compton scattering response of hydrogen is characterized 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 modelling 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 proton pool. The width of the momentum distribution, the value of kinetic energy and the effective force constant of the potential of the mean force underlying this distribution have been obtained for the first time for the quasi-free atomic hydrogen resulting from the hydrogen spillover process.

Contact : tellier@ill.fr

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