Mechanochemical reactions and hydrogen storage capacities in MBH 4 –SiS 2 systems (M=Li or Na)
The hydrogen storage properties, and phase compositions of mechanochemically prepared mixtures of xMBH 4 -SiS 2 (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 °C with a T onset of 88 °C without detectable diborane emission. The dehydrogenated sample reversibly absorbs 1.5 wt % of H 2 at 385 °C under 160 bar pressure. The H 2 release from materials with varying LiBH 4 :SiS 2 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 LiBH 4 SiS 2 system consist of one-dimensional chains of edge-sharing SiS 4/2 tetrahedra in which the non-bridging S-ends are terminated with Li + , which are further coordinated to the [BH 4 ] – anions. Here, a variety of possible polymorphs in the Li—Si—S-(BH 4 ) composition space have been identified using first principles and thermodynamic modeling that supports the likelihood of formation of such novel complexes.