Inelastic Neutron Scattering, A Unique Tool to Study Hydrogen In Materials

Inelastic neutron scattering can measure the vibrational spectra of materials on the whole range of vibrational motions (0-4400 cm−1) and effectively open up the field of neutron spectroscopy [1]. INS is a technique mainly used to study hydrogen-containing materials due to the high cross-section of hydrogen [2].<br/>The VISION spectrometer at the SNS in Oak Ridge, Tennessee, has increased overall flux at low energy transfers up to 40 times over its competitors and has unprecedented sensitivity.<br/>In this paper, the author will present examples of the technique's unique capabilities for studying metal hydrides and molecular hydrogen in confinement.<br/>In ZrVH2, the inelastic neutron scattering spectra analysis reveals that these structures originate from hydrogen vibrations confined by neighboring hydrogens, partially at distances as short as 1.6 Å. This is an experimental demonstration of the violation of Switendick's criterion, which predicts the minimal possible hydrogen-hydrogen distance in a metal hydride is around 2.1Å.[3]<br/>Inelastic neutron scattering (INS) and neutron diffraction (ND) experiments were performed at the VISION beamline, demonstrating the existence of rapid and efficient hydrogen clathrate hydrate formation in a confined nanospace. It shows that specially designed activated carbon materials can surpass these obstacles of hydrogen clathrate formation by acting as nanoreactors promoting the nucleation and growth of H2 hydrates. The confinement effects in the inner cavities promote massive growth of hydrogen hydrates at moderate temperatures, using pure water, with high-speed kinetics, and at lower pressures than the bulk system. [4]<br/>Adsorption on various adsorbents of hydrogen and helium at temperatures close to their boiling points shows, in some cases, unusually high monolayer capacities. Theoretical and INS studies of molecular hydrogen on mesoporous silica demonstrate the formation of such a super-dense phase. [5]<br/><br/>[1] Mitchell, P.C., Parker, S.F., Ramirez-cuesta, T.A. and Tomkinson, J. eds., 2005. Vibrational Spectroscopy with Neutrons-With Applications In Chemistry, Biology, Materials Science And Catalysis (Vol. 3). World Scientific.<br/>[2] Ramirez-Cuesta, A.J., Jones, M.O. and David, W.I., 2009. Neutron scattering and hydrogen storage. Materials Today, 12(11), pp.54-61.<br/>[3] Borgschulte, A., Terreni, J., Billeter, E., Daemen, L., Cheng, Y., Pandey, A., Lodziana, Z., Hemley, R.J. and Ramirez-Cuesta, A.J., 2020. Inelastic neutron scattering evidence for anomalous H–H distances in metal hydrides. Proceedings of the National Academy of Sciences, 117(8), pp.4021-4026.<br/>[4] Farrando-Perez, Judit, Rafael Balderas-Xicohtencatl, Yongqiang Cheng, Luke Daemen, Carlos Cuadrado-Collados, Manuel Martinez-Escandell, Anibal J. Ramirez-Cuesta, and Joaquin Silvestre-Albero. "Rapid and efficient hydrogen clathrate hydrate formation in confined nanospace." Nature communications 13, no. 1 (2022): 1-6.<br/>[5] Balderas-Xicohténcatl, R., Lin, H.H., Lurz, C., Daemen, L., Cheng, Y., Cychosz Struckhoff, K., Guillet-Nicolas, R., Schütz, G., Heine, T., Ramirez-Cuesta, A.J. and Thommes, M., 2022. Formation of a super-dense hydrogen monolayer on mesoporous silica. Nature Chemistry, pp.1-6.