An exciting synergistic effect: realizing large-sized MgH₂ dehydrogenation at lowered temperatures by locally assembling a heterophase composite

Fascinating hydrogen sorption properties of MgH₂ are usually achieved by alloying, catalyzing, surface modification, and in most cases, nanosizing of either the grains or the particles because the bulk MgH₂ is difficult to desorb H₂ at mild conditions. Here an efficiently synergistic strategy to tune the desorption behavior of micro-sized MgH₂ is proposed. Through a well-designed solid state hydriding combustion synthesis (HCS) process, Mg–Ni hydrides distribute uniformly throughout the whole particle, locally forming a multi-phase hydrides system. The whole hydrogen content is released at a lowered temperature characteristic of Mg₂NiH₄ (210–240 °C). Desorption temperature of MgH₂ in the multi-phase hydrides system is decreased by 173 °C and dehydrogenation activation energy is reduced by half compared with that of the simple mixture. A simultaneous desorption process of the multi-phase hydrides is firstly demonstrated by in situ X-ray diffraction, based on which a remarkable synergistic desorption mechanism is proposed, owing to the interfacial engineering and catalyzing effect of Mg₂Ni. Fresh insights into the cooperative effect between the distinct hydrides and other related complex systems are presented as well: when properly coupled, large bulk state hydrides (>20 μm) can also exhibit desirable practical behaviors, even in the absence of additional catalysts or modifying agents.