15 - Borohydrides as hydrogen storage materials

Abstract

Publisher Summary Borohydrides belong to a class of materials with the highest gravimetric hydrogen densities. There are many types of borohydrides depending on the composition of M, B and H, for example, M(BH4)n, M(B3H8)n, M(B6H6)n, M(B9H9)n and M(B12H12)n. This chapter focuses on M(BH4)n, tetrahydridoborate/tetrahydroborate. The study of M(BH4)n is important area of for research in the use of complex hydrides as hydrogen storage materials for some reasons and the chapter highlights these reasons. The chapter summarizes the basic properties of M(BH4)n and presents the synthesis methods and clarified structures of it. It also shows the general reaction of dehydrogenation and re-hydrogenation and thermodynamics and kinetics properties. It reports the crystal structures of some M(BH4)n and the determination of those structures and finding the correlation between structures and hydrogen storage properties are important for future development. Thermodynamic stability for M(BH4)n can be systematically predicted by considering the electro negativity of M. Based on the correlation, one can expect that M(BH4)n with appropriate stability and high hydrogen density. The investigation of M(BH4)n with appropriate stability is of great importance in the development of hydrogen storage material. To achieve fast reaction kinetics is another important research direction. For this purpose, finding an appropriate additive (dopant) and using a new heating system such as an electromagnetic field might be useful. Also using an intermediate phase and considering a low melting temperature might provide a useful way for promoting the reaction kinetics and achieving the reversible reaction under moderate conditions. The chapter further reviews the current potentiality and outlook for hydrogen storage and presents the earlier works on the borohydrides.