We study the kinetics of hydrogen sorption in Mg-Ti-H nanoparticles prepared by gas phase condensation of mixed Mg-Ti vapors under a H2-containing atmosphere. Four samples with different Ti contents from 14 to 63 at.% Ti are examined in the 100− 150 C range. The hydrogen absorption kinetics coupled with the formation of MgH2 can be described a nucleation and growth model. The activation energy is in the range 43− 52 kJ/mol and the rate constant (at 150 C) increases from 27∙ 10 s-1 to 92∙ 10 s-1 with increasing Ti content. Hydrogen desorption is well modeled by a sequence of surface-limited and contracting-volume kinetics, except at the highest Ti content where nucleation and growth is observed. The activation energy of surface-limited kinetics is~ 32 kJ/mol. The rate constant (at 150 C) increases from 0.5∙ 10 s-1 to 1.2∙ 10 s-1 with the Ti content. These results open an unexplored kinetic window for Mg-based reversible hydrogen storage close to ambient temperature.
1 Jan 2019