Role of chemical interaction between MgH₂ and TiO₂ additive on the hydrogen storage behavior of MgH₂

Highlights: • Reaction of MgH₂ + xTiO₂ (x = 0.25, 0.33, 0.5 and 1) mixture has been investigated. • The additive TiO₂ transforms as an in-built Mg_xTi_yO_x+y rock salt nanocatalyst. • Catalytic activity of Mg_xTi_yO_x+y varies with respect to the dissolved Ti content. • The reason for the high activation energy in cycled MgH₂ samples is explained. - Abstract: The present study explores how the additive titania chemically reacts with magnesium hydride and influences the dehydrogenation of MgH₂. Quantitative X − ray diffraction study of ball milled MgH₂ + xTiO₂ (x = 0.25, 0.33, 0.5 and 1) suggests that Ti substituted MgO is the main reaction product in all the product powders. Convincing evidence is obtained to conclude that Ti dissolution in MgO makes a dramatic behavioral change to MgO; passive MgO turns as an active in-built catalyst. The analysis correlating the dehydrogenation kinetics, composition of in-situ catalyst and sample durability suggests that effectiveness of Ti substituted MgO (Mg_xTi_yO_x+y) as a catalyst for MgH₂ depends on the concentration of Ti in Mg_xTi_yO_x+y rock salt. These observations are immensely helpful for understanding the hydrogen desorption mechanism of metal oxide additives loaded MgH₂ system.