Transformation of Metallic Ti to TiH2 Phase in the Ti/MgH2 Composite and Its Influence on the Hydrogen Storage Behavior of MgH2

Abstract

The current work explores the in-situ formation of TiH₂ additive in a Ti/MgH₂ nanocomposite system. Mild mechanical milling leaves Ti chemically unchanged, while formation of stable TiH_2-x occurs upon strong mechanical milling. TiH_2-x further transforms to TiH₂ upon recycling the powder (dehydrogenation and subsequent hydrogenation) and lowers the activation energy of MgH₂ to 89.4 kJ (mol H₂ )^-1 [E_a of as-received MgH₂ is 153 kJ (mol H₂ )^-1 ]. This work also reiterates that metallic Ti additive mixed MgH₂ requires strong mechanical milling for better H₂ ab/de-sorption performance. The current observations support the view that lattice strain may be an important factor in the catalysis of additives incorporated MgH₂ hydrogen storage systems.

Keywords: Additives; catalytic mechanism; hydrogen storage; reaction kinetics; surface reaction.