Main content area

Improved hydrogen desorption properties of MgH2 by graphite and NiF2 addition: experimental and first-principles investigations

Zhang, J., Qu, H., Yan, S., Yin, L. R., Yu, X. F., Zhou, D. W.
Journal of materials science 2017 v.52 no.14 pp. 8681-8689
X-ray diffraction, additives, dehydrogenation, desorption, differential scanning calorimetry, enthalpy, graphene, hydrides, hydrogen, milling, scanning electron microscopy, temperature
The high dehydrogenation temperature is still the impediment for the practical application of magnesium-based hydride (MgH₂) as a potential hydrogen storage medium. In order to improve the hydrogen desorption properties of MgH₂, the graphite and NiF₂ are selected as additives, and the MgH₂–graphite and MgH₂–graphite–NiF₂ composites are prepared by high-energy ball milling. Using experimental X-ray diffraction, scanning electron microscopy, differential scanning calorimetry characterizations and first-principle calculations, the effects and mechanisms of graphite and NiF₂ addition on the hydrogen desorption properties of MgH₂ are systematically investigated. Experimental results show that the single addition of graphite is beneficial to the refinement of MgH₂ grains and particles. The size of MgH₂ particles can be further decreased after the co-addition of graphite and NiF₂. Either the single addition of graphite or the co-addition of graphite and NiF₂ reduces the dehydrogenation temperature of MgH₂. As compared with pure milled MgH₂, the dehydrogenation peak temperatures are decreased by 31 and 63 °C for MgH₂–graphite and MgH₂–graphite–NiF₂ composites, respectively. Apparently, the co-addition of graphite and NiF₂ exhibits the synergistic catalytic effects in improving the hydrogen desorption properties of MgH₂. The first-principle calculations reveal that the co-addition of graphite and NiF₂ leads to the structural distortion of MgH₂ and results in the charge transfer between the additives and MgH₂, which induce the weakened structural stability and decreased dehydrogenation enthalpy of MgH₂. These may be the underlying reasons for the reduced dehydrogenation temperature of MgH₂ with graphite and NiF₂ addition.