Enhancing hydrogen storage properties of MgH2 through addition of Ni/CoMoO4 nanorods

In this work, one-dimensional NiMoO4 and CoMoO4 nanorods are prepared and introduced into MgH2 to improve its hydrogen storage properties. It is observed that the MgH2–NiMoO4 system exhibits lower dehydrogenation temperature and faster kinetics than the MgH2–CoMoO4 system and pure MgH2, indicating the superior promoting effect of NiMoO4 over CoMoO4. Concretely, NiMoO4 reacts with MgH2 during the first dehydrogenation to in situ form Mg2Ni and Mo0, both of which are crucial factors for the following hydrogen cycling process. The 'Mg2Ni/Mg2NiH4' mutual transformation upon hydrogen release/uptake is the well-known 'hydrogen pump' effect which boosts the hydrogen storage performance of MgH2. Moreover, theoretical calculations reveal the dual roles of Mo0 played for the hydrogen storage in MgH2: i) it accelerates the hydrogen de/absorption of MgH2 through weakening the Mg–H bonding; ii) it facilitates the mutual 'Mg2Ni/Mg2NiH4' transformation as the formation energy of Mg2NiH4 decreases under the influence of Mo0, which we call 'facilitated hydrogen pump' effect in this work. Ascribing to the collaborative action between Ni- and Mo- containing species, the hydrogen storage kinetics of MgH2 has been accelerated.