Improvement in the Hydrogen-Storage Properties of Mg₂Ni by Adding LiBH₄

Abstract

To improve the hydrogen-storage properties of Mg₂Ni, LiBH₄ was added by milling in hydrogen atmosphere (reactive mechanical milling, RMM). Mg₂Ni-10LiBH₄ was prepared with a composition of 90 wt% Mg₂Ni + 10 wt% LiBH₄. The quantity of released hydrogen (H_r) versus temperature T curve for Mg₂Ni10LiBH₄ 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 Mg₂Ni10LiBH₄ showed that this sample contained Mg₂Ni, Mg₂NiH₄, o-LiBH₄, h-LiBH₄, Ni, and MgH₂. 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-LiBH₄ and h-LiBH₄. The peak at 563 K is for the hydrogen release from Mg₂NiH₄ and the peak at 600 K is for the hydrogen release from Mg₂NiH₄ and MgH₂. The RMM of Mg₂Ni with added LiBH₄ 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.