Structural and enhanced hydrogen storage properties of the Li12Mg3Si3Al phase

Abstract

The multicomponent alumosilicide Li₁₂Mg₃Si₃Al (cubic, space group I-43d, cI76) belongs to the structural family based on the Cu₁₅Si₄ type. The Li atoms are ordered and occupy the site with symmetry 1 and the Mg atoms occupy the site with -4.. symmetry. The Si/Al statistical mixture occupies the site with .3. symmetry. The coordination polyhedra around the Li atoms are 13-vertex distorted pseudo-Frank-Kasper polyhedra. The environments of the Mg and Si/Al atoms are icosahedral. The hydrogen storage characteristics of Li₁₂Mg₃Si₃Al were investigated. The reversible hydrogen storage capacity of the title compound is excellent and the gravimetric storage capacity of this new material, corresponding to 9.1 wt% H₂, is higher compared to Li₁₂Mg₃Si₄ (8.8 wt%). The enthalpy of hydrogen desorption is 86 kJ mol^-1 and is lower compared to known lithium-based hydrides.

Keywords: crystal structure; hydrogen storage material; hydrogenation; intermetallic; lithium and magnesium alloy; quaternary alloy.