Investigation of Effect of Milling Atmosphere and Starting Composition on Mg2FeH6 Formation

Alexandre Asselli,Jacques Huot

doi:10.3390/met4030388

Abstract

In this study we investigated the synthesis and the hydrogen storage properties of Mg2FeH6. The complex hydride was prepared by ball milling under argon and hydrogen atmosphere from 2Mg + Fe and 2MgH2 + Fe compositions. The samples were characterized by X-ray powder diffraction and scanning electron microcopy. Kinetics of hydrogen absorption and desorption were measured in a Sievert’s apparatus. We found that the milling atmosphere plays a more important role on Mg2FeH6 synthesis than the starting compositions. Ball milling under hydrogen pressure resulted in smaller particles sizes and doubled the yield of Mg2FeH6 formation. Despite the microstructural differences after ball milling, all samples had similar hydrogen absorption and desorption kinetics. Loss of capacity was observed after only five cycles of hydrogen absorption/desorption.

Highlights

The complex hydride Mg2FeH6 has the highest known volumetric density of hydrogen (150 kg m−3), which is more than twice higher than hydrogen in liquid state (70.8 kg m−3) [1]
The X-ray powder diffraction (XRPD) patterns show that Mg2FeH6 was synthesized by ball milling regardless of starting compositions and milling atmospheres
We investigated the effect of milling atmosphere and starting compositions on Mg2FeH6 formation

Summary

Introduction

The complex hydride Mg2FeH6 has the highest known volumetric density of hydrogen (150 kg m−3), which is more than twice higher than hydrogen in liquid state (70.8 kg m−3) [1]. This high hydrogen density is attractive for solid-state hydrogen storage applications. In 1984, Didisheim et al [4] reported the first synthesis of Mg2FeH6 by sintering the metallic elements at high temperature (450–520 °C) under hydrogen pressure (20–120 bar) during several days (2–10 days). Selvan and Yvon [5] showed that the most convenient condition to synthesize the Mg2FeH6 was by sintering of 2Mg + Fe at 450 °C under 90 bar of H2 pressure during 10 days. Huot et al [6]

Methods

Results

Conclusion