Tuning the structural stability of LiBH4 through boron-based compounds towards superior dehydrogenation

Abstract

The remarkable destabilization effects of H₃BO₃, HBO₂, and B₂O₃ on dehydrogenation of LiBH₄ are revealed in this work. The effectiveness of destabilizing the structural stability is in the order of H₃BO₃ > HBO₂ > B₂O₃. Besides, through optimizing the molar ratio of LiBH₄ and H₃BO₃ and milling treatment, the destabilization effect, especially for dehydrogenation kinetics, is further enhanced. For example, at a temperature as low as 110 °C, 5.8 wt% hydrogen can be liberated in seconds from 2LiBH₄–H₃BO₃ prepared through pre-milling. The investigation reveals that each of the LiBH₄–H₃BO₃, LiBH₄–HBO₂ and LiBH₄–B₂O₃ systems undergo multiple dehydrogenation stages corresponding to different destabilization mechanisms. The reaction at lower temperature is ascribed to the H⁺⋯H⁻ coupling mechanism which should be enhanced by the [OH]⁻⋯[BH₄]⁻ interaction mode. Pre-milling treatment of LiBH₄ and H₃BO₃ also promotes the H⁺⋯H⁻ interaction which may have originated from the increasing contact area as a result of the fine particles, and therefore probably reduced the reaction activation energy. Consequently, it gives rise to the superior dehydrogenation performance of lower temperature, rapid kinetics, pure hydrogen and high capacity, which are required for off-board hydrogen energy vehicle application.