Hydrogen storage properties of eutectic metal borohydrides melt-infiltrated into porous Al scaffolds

Abstract

Porous Al scaffolds were synthesised and melt-infiltrated with various eutectic metal borohydride mixtures (0.725LiBH4-0.275KBH4, 0.68NaBH4-0.32KBH4, 0.4NaBH4-0.6 Mg(BH4)2) to simultaneously act as both a confining framework and a reactive destabilising agent for H2 release. The scaffolds were synthesised by sintering a pellet of NaAlH4/2 mol%TiCl3 at 450 °C under dynamic vacuum. During the sintering process the sodium alanate (NaAlH4) decomposed to Al metal. The vacuum applied at elevated temperature promoted the Na metal to vaporise and be extruded from the pellet. The pores of the resulting Al scaffold were created during removal of the H2 and the Na from the body of the NaAlH4/2 mol%TiCl3 pellet. According to the morphological observations carried out by a Scanning Electron Microscope (SEM), melt-infiltrated eutectic mixtures of metal borohydrides were highly dispersed into the porous scaffolds. Temperature Programmed Desorption (TPD) experiments, revealed that the melt-infiltrated samples exhibited faster H2 desorption kinetics in comparison to bulk samples, with onset temperatures (Tdes) lower than the bulk by 150–250 °C. The as-synthesised porous Al scaffolds acted as a reactive containment vessel for these eutectic mixtures that simultaneously nanoconfined and destabilised the mixtures.