Fast Hydrogen Sorption Kinetics in Mg-VCl₃ Produced by Cryogenic Ball-Milling

Hydrogen storage in Mg/MgH₂ materials is still an active research topic. In this work, a mixture of Mg-15wt.% VCl₃ was produced by cryogenic ball milling and tested for hydrogen storage. Short milling time (1 h), liquid N₂ cooling, and the use of VCl₃ as an additive produced micro-flaked particles approximately 2.5-5.0 µm thick. The Mg-15wt.% VCl₃ mixture demonstrated hydrogen uptake even at near room-temperature (50 °C). Mg-15wt.% VCl₃ achieved ~5 wt.% hydrogen in 1 min at 300 °C/26 bar. The fast hydriding kinetics is attributed to a reduction of the activation energy of the hydriding reaction (E_{a hydriding} = 63.8 ± 5.6 kJ/mol). The dehydriding reaction occurred at high temperatures (300-350 °C) and 0.8-1 bar hydrogen pressure. The activation energy of the dehydriding reaction is 123.11 ± 0.6 kJ/mol. Cryomilling and VCl₃ drastically improved the hydriding/dehydriding of Mg/MgH₂.