Hydrogen sorption properties of graphite-modified magnesium nanocomposites prepared by ball-milling

Abstract

The hydrogen absorption–desorption characteristics of the nanocomposites 90 wt.% Mg 2Ni–10 wt.% C (graphite) and 75 wt.% Mg–15 wt.% Mg 2Ni–10 wt.% C obtained by mechanical alloying have been investigated. Modification with graphite has been found to improve the hydriding kinetics of Mg 2Ni at a temperature of 573 K and below. The composite 75 wt.% Mg–15 wt.% Mg 2Ni–10 wt.% C has a high hydrogen absorption capacity and is characterised by very good kinetic parameters of hydriding at 473 and 423 K. Modification of the surface of this composite with graphite accelerates the desorption of hydrogen. The results obtained as well as the XPS data have confirmed the opinion expressed previously by several authors about the effect of graphite on the magnesium oxide layer present on the composite surface during hydriding. The difference observed between the dehydriding rates of the two graphite-containing composites is probably due to a difference in size of the interface formed on both magnesium systems as a result of hydrogen absorption.