Remarkable hydrogen storage properties for nanocrystalline MgH2 synthesised by the hydrogenolysis of Grignard reagents

Abstract

The possibility of generating MgH₂ nanoparticles from Grignard reagents was investigated. To this aim, five Grignard compounds, i.e. di-n-butylmagnesium, tert-butylmagnesium chloride, allylmagnesium bromide, m-tolylmagnesium chloride, and methylmagnesium bromide were selected for the potential inductive effect of their hydrocarbon group in leading to various magnesium nanostructures at low temperatures. The thermolysis of these Grignard reagents was characterised in order to determine the optimal conditions for the formation of MgH₂. In particular, the use of di-n-butylmagnesium was found to lead to self-assembled and stabilized nanocrystalline MgH₂ structures with an impressive hydrogen storage capacity, i.e. 6.8 mass%, and remarkable hydrogen kinetics far superior to that of milled or nanoconfined magnesium. Hence, it was possible to achieve hydrogen desorption without any catalyst at 250 °C in less than 2 h, while at 300 °C, hydrogen desorption took only 15 min. These superior performances are believed to result from the unique physical properties of the MgH₂ nanocrystalline architecture obtained after hydrogenolysis of di-n-butylmagnesium.