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

Abstract

Abstract The hydrogen storage properties, and phase compositions of mechanochemically prepared mixtures of xMBH4-SiS2 (x\xa0=\xa02–8), where M\xa0=\xa0Li or Na, were investigated using gas sorption analysis, powder X-ray diffraction, and infrared and solid-state NMR spectroscopic methods. The 2LiBH4:1SiS2 system forms an amorphous product that releases ca. 4.3\xa0wt % of H2 below 385\xa0°C with a Tonset of 88\xa0°C without detectable diborane emission. The dehydrogenated sample reversibly absorbs 1.5\xa0wt % of H2 at 385\xa0°C under 160\xa0bar pressure. The H2 release from materials with varying LiBH4:SiS2 ratios peaks at 8.2\xa0wt % for the 6LiBH4:1SiS2 composition, with a reversible hydrogen storage capacity of 2.4\xa0wt %. The H2 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.