Mechanochemical reactions and hydrogen storage capacities in MBH4-SiS2 systems (M=Li or Na)

The hydrogen storage properties, and phase compositions of mechanochemically prepared mixtures of xMBH(4)-SiS2 (x = 2-8), where M = Li or Na, were investigated using gas sorption analysis, powder X-ray diffraction, and infrared and solid-state NMR spectroscopic methods. The 2LiBH(4):1SiS(2) system forms an amorphous product that releases ca. 4.3 wt % of H-2 below 385 degrees C with a T-onset of 88 degrees C without detectable diborane emission. The dehydrogenated sample reversibly absorbs 1.5 wt % of H-2 at 385 degrees C under 160 bar pressure. The H-2 release from materials with varying LiBH4:SiS2 ratios peaks at 8.2 wt % for the 6LiBH(4):1SiS(2) composition, with a reversible hydrogen storage capacity of 2.4 wt %. The H-2 desorption capacities of the Li-containing systems surpass those of Na-containing systems. Solid-state NMR studies indicate that products of mechanochemical reactions in the LiBH4-SiS2 system consist of one-dimensional chains of edge-sharing SiS4/2 tetrahedra in which the non-bridging S-ends are terminated with Li+, which are further coordinated to the [BH4](-) anions. A variety of possible polymorphs in the Li-Si-S-(BH4) composition space have been identified using first principles and thermodynamic modeling that supports the likelihood of formation of such novel complexes. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.