EFFECT OF VARIOUS ADDITIVES ON THE HYDROLYSIS PERFORMANCE OF NANOSTRUCTURED MgH₂ SYNTHESIZED BY HIGH-ENERGY BALL MILLING IN HYDROGEN

Abstract

Magnesium hydride is a promising material for hydrogen generation via hydrolysis owing to high hydrogen storage capacity, mild reaction conditions, and low cost of magnesium metal. Unfortunately, the hydrolysis reaction of MgH₂ is rapidly hindered due to the formation of a passive Mg(OH)₂ layer. Various additives can be used to improve the efficiency of the reaction. The present study examines the influence of 5 wt.% EDTA and TiC–2TiB₂ additives on the hydrolysis of the nanostructured MgH₂ and compares it with the hydrolysis performance of pure MgH₂ and MgH₂ + 5 wt.% AlCl₃ for the first time. MgH₂ was synthesized by high-energy ball milling of Mg powder in hydrogen gas, while MgH₂-based nanocomposites were prepared either by mixing the obtained MgH₂ with 5 wt.% of additives or by milling Mg with 5 wt.% of additive in hydrogen. The synthesized MgH₂ is nanosized, containing a mixture of β-MgH₂ and high-pressure γ-modification of MgH₂. The hydrogen generation performance in terms of MgH₂ conversion rate and hydrogen yield was determined volumetrically. It was found that the MgH₂ + 5 wt.% EDTA composite displays the lowest reactivity among the tested materials, probably due to the interaction of MgH₂ with EDTA during the ball milling. Pure MgH₂ and MgH₂ + 5 wt.% (TiC–2TiB₂) composite demonstrate almost twice as better hydrolysis performance, which is, however, still quite far from application requirements. The maximum hydrogen yield of 557 mL/g MgH₂ and conversion rate of 30.3% was observed for MgH₂ + 5 wt.% AlCl₃ composition after 10 min of hydrolysis, which can be attributed to the destabilization of the Mg(OH)₂ layer by chlorine ions.