The Effect of High-Energy Ball Milling Conditions on Microstructure and Hydrogen Desorption Properties of Magnesium Hydride and Single-Walled Carbon Nanotubes

Nikita E. Kurdyumov,Viktor N. Kudiyarov,Roman R. Elman

doi:10.3390/met11091409

Abstract

Magnesium hydride is considered to be one of the most promising hydrogen storage materials, although it nevertheless has some problems, such as the high value of the activation energy of hydrogen desorption. To solve this problem, some scientists have proposed adding nanocarbon materials, in particular carbon nanotubes, to magnesium hydride. Currently, a detailed understanding of the mechanisms of obtaining composites based on magnesium hydride and carbon nanotubes is lacking, as is our understanding of the effect of nanocarbon additives on the activation energy and temperature of hydrogen desorption depending on the parameters of the composite synthesis. In addition, the data obtained at various values of milling parameters are very different, and in some works the effect of carbon nanomaterials on the hydrogen properties of magnesium hydride was not confirmed at all. Thus, it is important to determine the effect of nanocarbon additives on the properties of hydrogen storage of magnesium hydride under various milling parameters. This work is devoted to the study of the effect of nanocarbon additives on magnesium hydride and the determination of the dependences of the hydrogen desorption temperature and activation energy on the synthesis parameters. Composite powders containing MgH2 with 5 wt.% single-walled carbon nanotubes (SWCNT) were prepared using a planetary ball mill. The milling was carried out at various milling speeds, namely 300, 660, and 900 rpm. Results suggested that the structure of the nanotubes is preserved with prolonged grinding of magnesium hydride and SWCNT in a ball mill for 180 min at a relatively low grinding speed of 300 rpm. The composite obtained with these parameters has the lowest temperature of hydrogen desorption and an activation energy of H2 desorption of 162 ± 1 kJ/mol H2, which is 15% lower than that of the magnesium hydride MgH2 (189 ± 1 kJ/mol H2).

Highlights

The development of promising materials for hydrogen storage is one of the most important challenges for the improvement of hydrogen economy [1,2,3]
Within the course of the work, it was shown by scanning electron microscopy that an increase in the frequency of revolutions significantly affects the structure of carbon nanotubes, which are already destroyed after ball milling at 660 rpm for 60 min
A short milling time leads to an uneven distribution of carbon nanotubes in the volume of the MgH2–5 wt.% single-walled carbon nanotubes (SWCNT) composite and an unexpressed catalytic effect

Summary

Introduction

The development of promising materials for hydrogen storage is one of the most important challenges for the improvement of hydrogen economy [1,2,3]. One such effective and attractive hydrogen storage method is storage in metal hydrides. The use of magnesium as a reversible hydrogen storage material is problematic because of the high temperature (over 300 ◦C) [8,9] required for hydrogen desorption from magnesium hydride at an acceptable rate. This fact limits the use of magnesium hydride as a material for hydrogen storage

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