Influence
of Nickel and Silicon Addition on the Deuterium Siting and Mobility
in fcc Mg–Ti Hydride Studied with <sup>2</sup>H MAS NMR
- Publication date
- Publisher
Abstract
Fluorite-structured Mg–Ti
hydrides are interesting for hydrogen storage applications because
of their high gravimetric hydrogen storage capacity, and improved
(de)hydrogenation kinetics compared to MgH<sub>2</sub>. In the present
study we have investigated the potential catalytic effect of Ni and
Si as third element on the siting and mobility of electrochemically
loaded deuterium in ball-milled Mg<sub>0.63</sub>Ti<sub>0.27</sub>Ni<sub>0.10</sub> and Mg<sub>0.63</sub>Ti<sub>0.27</sub>Si<sub>0.10</sub> alloys. Magic angle spinning (MAS) <sup>2</sup>H NMR reveals that
Ni and Si induce new types of deuterium sites in addition to the Mg-rich
and Ti-rich sites already present in Mg<sub>0.65</sub>Ti<sub>0.35</sub>D<sub>1.2</sub>. 2D exchange NMR spectroscopy shows a substantial
deuterium exchange between the various types of sites, which reflects
their close interconnectivity in the crystal structure. Furthermore,
the time scale and temperature dependence of the deuterium mobility
have been quantified by 1D exchange NMR. The obtained effective residence
times for deuterium atoms in the Mg-rich and Ti-rich nanodomains in
Mg<sub>0.65</sub>Ti<sub>0.35</sub>D<sub>1.2</sub>, Mg<sub>0.63</sub>Ti<sub>0.27</sub>Ni<sub>0.10</sub>D<sub>1.3</sub>, and Mg<sub>0.63</sub>Ti<sub>0.27</sub>Si<sub>0.10</sub>D<sub>1.1</sub> at 300 K are 0.4,
0.3, and 0.8 s, respectively, and the respective apparent activation
energies 17, 21, and 27 kJ mol<sup>–1</sup>. The addition of
Ni promotes deuterium mobility inside Mg–Ti hydrides, which
is in agreement with the observed catalytic effect of Ni on the electrochemical
(de)hydrogenation of these materials
