Synthesis and Hydrogen Storage Behaviour of Pure Mg₂FeH₆ at Nanoscale

Abstract

Pure Mg₂FeH₆ compounds with two different morphologies have been successfully synthesized directly by mechanical milling (MM) and sintering of a mixture of 2Mg+Fe nanoparticles under an H₂ atmosphere, respectively. The successful preparation of pure Mg₂FeH₆ can be attributed to the small particle sizes of Mg and Fe nanoparticles prepared by hydrogen plasma-metal reaction (HPMR), which provides shorter diffusion distance for hydrogen and the metals. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that the Mg₂FeH₆ synthesized by mechanical milling has larger particle size but smaller crystallite size compared with the Mg₂FeH₆ synthesized by sintering. The Mg₂FeH₆ synthesized by mechanical milling can desorb more than 4.5 mass% hydrogen in 10 min under an initial hydrogen pressure of 0.001 bar at 573 K. Compared with the Mg₂FeH₆ synthesized by sintering under the same conditions as the Mg₂FeH₆ synthesized by mechanical milling, it is suggested that decrease of crystallite size is beneficial for enhancing desorption property of Mg₂FeH₆.