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 Mo-0, 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 Mo-0 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/Mg-2 NiH4' transformation as the formation energy of Mg2NiH4 decreases under the influence of Mo-0, 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. (C) 2020 Elsevier Ltd. All rights reserved.