Affiliation:
1. Laboratory for Advanced Analytical Technologies Swiss Federal Laboratories for Materials Science and Technology Empa Überlandstrasse 129 Dübendorf CH‐8600 Switzerland
2. Department of Chemistry University of Zurich Winterthurerstrasse 190 Zürich CH‐8057 Switzerland
3. Institute of Nuclear Physics Polish Academy of Sciences Krakow PL‐31342 Poland
Abstract
AbstractProvision of atomic hydrogen by hydrogen dissociation catalysts only moderately accelerates the hydrogenation rate of magnesium. They shed light on this well‐known but technically challenging fact through a combined approach using an unconventional surface science technique together with Density Functional Theory (DFT) calculations. The calculations demonstrate the drastic electronic structure changes during transformation of Mg to MgH2, which make fractional hydrogen coverage on the surface, as well as substoichiometric hydrogen content in the bulk energetically unfavorable. Reflecting Electron Energy Loss Spectroscopy (REELS) is used to measure the surface and bulk plasmon during hydrogen sorption in magnesium. The measurements show that the hydrogenation proceeds via the growth of magnesium hydride without the presence of chemisorbed hydrogen on the metallic magnesium surface exactly as indicated by the calculations. This is due to the low stability of sub‐stoichiometric amounts of chemisorbed H correlating with the unfavorable charge state of Mg. They are merely bound to the unchanged adjacent Mg layers, thereby explaining the failure of classical hydrogenation catalysts, which effectively only hydrogenate Mg in their direct vicinity. The acceleration of hydrogen sorption kinetics in Mg must affect the polarization in the interface between Mg and MgH2 during hydrogenation.
Funder
Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung
Academic Computer Centre Cyfronet, AGH University of Science and Technology
UZH Foundation
Subject
General Physics and Astronomy,General Engineering,Biochemistry, Genetics and Molecular Biology (miscellaneous),General Materials Science,General Chemical Engineering,Medicine (miscellaneous)