Vanadium induces Ni-Co MOF formation from a NiCo LDH to catalytically enhance the MgH2 hydrogen storage performance

Abstract

Magnesium-based hydrogen storage materials, such as MgH₂, have attracted considerable attention because of its superior hydrogen storage capacities, inexpensive, and excellent reversibility. However, their high thermodynamic stabilities and slow kinetics lead to relatively high desorption temperatures, which severely limit the wide application of MgH₂. In this study, the inclusion of vanadium induced the formation Ni-Co metal–organic frameworks (MOF) from a NiCo layered double hydroxide (LDH), thereby increasing the number of defects and vacancies, and improving the hydrogen storage properties of MgH₂. The synthesized NiCo-MOF/V-O-doped MgH₂ system demonstrates excellent hydrogen storage capacity. More specifically, 5 wt.% of H₂ was released over 20 min at a relatively low dehydrogenation temperature of 250 °C, and almost complete dehydrogenation was achieved at 300 °C for 5 min. In addition, at 125 °C, the hydrogen storage material absorbed 5.5 wt.% H₂ in 10 min. Furthermore, the activation energy of dehydrogenation was determined to be 69.588 ± 6.302 kJ ·mol⁻¹ which is significantly lower than that of the ball-milled MgH₂ (i.e., 118.649 ± 2.825 kJ ·mol⁻¹). It was therefore inferred that during dehydrogenation process, a Mg₂Ni/Mg₂NiH₄ hydrogen pump is formed by Ni, while the V-H and Co-H bonds formed by Co and V during the reaction act synergistically to catalyze the absorption and desorption of hydrogen, thereby increasing the hydrogen storage capacity of MgH₂. These experiments provide new perspectives on the commercial application of MgH₂.