Direct Rehydrogenation of LiBH4 from H-Deficient Li2B12H12−x

Yigang Yan,Weitong Cai,Hui Wang,Arndt Remhof,Min Zhu,Daniel Rentsch

doi:10.3390/cryst8030131

Abstract

Li2B12H12 is commonly considered as a boron sink hindering the reversible hydrogen sorption of LiBH4. Recently, in the dehydrogenation process of LiBH4 an amorphous H-deficient Li2B12H12−x phase was observed. In the present study, we investigate the rehydrogenation properties of Li2B12H12−x to form LiBH4. With addition of nanostructured cobalt boride in a 1:1 mass ratio, the rehydrogenation properties of Li2B12H12−x are improved, where LiBH4 forms under milder conditions (e.g., 400 °C, 100 bar H2) with a yield of 68%. The active catalytic species in the reversible sorption reaction is suggested to be nonmetallic CoxB (x = 1) based on 11B MAS NMR experiments and its role has been discussed.

Highlights

Hydrogen is considered to be an ideal synthetic energy carrier to replace the limited quantity of fossil fuels available
The decomposition pathway of LiBH4 depends on temperature and H2 pressure with Li2 B12 H12 formed as the main intermediate compound following a two-step route [10,13]: LiBH4 → 5/6 LiH + 1/12 Li2 B12 H12 + 13/12 H2 → LiH + B + 3/2 H2 (1)
We systematically investigated the rehydrogenation properties of Li2 B12 H12−x to form LiBH4

Summary

Introduction

Hydrogen is considered to be an ideal synthetic energy carrier to replace the limited quantity of fossil fuels available. Lithium borohydride (LiBH4 ), exhibiting a hydrogen density of 18.5 wt %, is one of the currently most discussed lightweight complex hydrides [7,8,9,10,11,12,13,14,15,16,17,18]. It crystalizes in two polymorphs, with structural transition from an orthorhombic low-temperature phase to a hexagonal high-temperature (HT) phase above 110 ◦ C [7]. The decomposition pathway of LiBH4 depends on temperature and H2 pressure with Li2 B12 H12 formed as the main intermediate compound following a two-step route [10,13]: LiBH4 → 5/6 LiH + 1/12 Li2 B12 H12 + 13/12 H2 → LiH + B + 3/2 H2

Results

Discussion

Conclusion