Thermodynamic tuning of lithium borohydride using various metallic sources

Abstract

Lithium borohydride (LiBH4) has been shown great interest as a hydrogen storage material owing to its large hydrogen storage capacity of 18.5 wt%, but unfortunately to release the vast majority of the stored hydrogen requires temperatures in excess of 600 °c. To improve the temperature at which LiBH4 decomposes, and to improve its poor reversibility, a process known as thermodynamic tuning can be used. Thermodynamic tuning involves creating new, more favourable reaction pathways and in this work the addition of nickel, silicon, iron and cobalt were investigated. The addition of nickel in the LiBH4:2Ni system was shown to be the most effective in reducing the decomposition temperature to occur below 300 °c while also improving reversibility to occur in the solid state at temperatures of 250 °c or lower. The addition of silicon was found to not be effective in reducing the decomposition temperature of LiBH4 even though it was thermodynamically predicted to do so. Attempts to improve the kinetics of the system with a titanium catalyst only showed an improvement when large quantities of the catalyst were used implying that the reaction with the catalyst was the driving force. Addition of both cobalt and iron were also effective in reducing the temperature of LiBH4 decomposition, in a similar reaction to the nickel systems by forming borides. The mass loss in the solid state (<300 °c) was, however, inferior to the addition of nickel