Improvement in the Hydrogen-Storage Properties of Mg<sub>2</sub>Ni by Adding LiBH<sub>4</sub>

Abstract

To improve the hydrogen-storage properties of Mg<sub>2</sub>Ni, LiBH<sub>4</sub> was added by milling in hydrogen atmosphere (reactive mechanical milling, RMM). Mg<sub>2</sub>Ni-10LiBH<sub>4</sub> was prepared with a composition of 90 wt% Mg<sub>2</sub>Ni + 10 wt% LiBH<sub>4</sub>. The quantity of released hydrogen (H<sub>r</sub>) versus temperature T curve for Mg<sub>2</sub>Ni10LiBH<sub>4</sub> was obtained by heating at a rate of 4~5 K in 1.0 bar hydrogen. The hydrogen-storage properties of the sample were investigated. The phases formed were examined from the x-ray diffraction (XRD) patterns of the samples after RMM, and after hydrogen-absorption and release cycling. The XRD pattern of Mg<sub>2</sub>Ni10LiBH<sub>4</sub> showed that this sample contained Mg<sub>2</sub>Ni, Mg<sub>2</sub>NiH<sub>4</sub>, o-LiBH<sub>4</sub>, h-LiBH<sub>4</sub>, Ni, and MgH<sub>2</sub>. The dHr/dT versus T curve exhibited three peaks at 325 K, 563 K, and 600 K, respectively. The peak at 325 K is for the hydrogen release from o-LiBH<sub>4</sub> and h-LiBH<sub>4</sub>. The peak at 563 K is for the hydrogen release from Mg<sub>2</sub>NiH<sub>4</sub> and the peak at 600 K is for the hydrogen release from Mg<sub>2</sub>NiH<sub>4</sub> and MgH<sub>2</sub>. The RMM of Mg<sub>2</sub>Ni with added LiBH<sub>4</sub> creates defects and cracks. RMM facilitates nucleation, increases reactivity, and shortens the diffusion distances of hydrogen atoms. Expansion and contraction of lattices due to cycling has effects similar to, but weaker than, the effects of RMM.