Computational Design of Dual Cation Ammine Metal Borohydrides: LiTi(BH4)5(NH3)X

Abstract

Global energy need is mostly fulfilled via fossil fuels. Usage of these sources causes harmful consequences to both environment and human beings. Besides, they have limited reserves and therefore alternative fuels must be discovered. Hydrogen is one of these alternatives due to its high energy content and environmentally friendly nature. However, there are many challenging problems waiting to be addressed for its widespread use. One of them is hydrogen storage which is especially very important for on-board applications. Even hydrogen can be stored as in the form of gas or liquid, these mediums are not practical in everyday use. As an alternative, hydrogen can also be stored in the solid form. For this purpose, both metal borohydrides and ammines are proposed due to their high gravimetric and volumetric densities. Metal borohydrides have some severe drawbacks e.g., requirement of a very high temperature for the hydrogen decomposition. Therefore, they can be mixed with ammines to produce new materials with a better thermodynamics. Dual-cation ammine metal borohydrides (AMBs) just suit well for this purpose. In this study, we computationally designed new AMBs in the form of LiTi(BH4)5(NH3)x x = 2, 3, 4 using a strategy which combines crystal structure prediction with density functional theory computations.