Significantly improved de/rehydrogenation properties of lithium borohydride modified with hexagonal boron nitride

Abstract

The remarkable hydrogen de/absorption properties of lithium borohydride are achieved by mechanically milling LiBH₄ with hexagonal boron nitride (h-BN). It is found that the dehydrogenation properties of LiBH₄ are improved with increasing the amount of h-BN. The 30 mol% h-BN doped LiBH₄ composite starts to release hydrogen from just 180 °C, which is 100 °C lower than the onset dehydrogenation temperature of ball milled LiBH₄. Moreover, the 30 mol% h-BN doped LiBH₄ composite can release 12.6 wt% hydrogen in 2 h at 400 °C, while only 0.98 wt% H₂ is gained from ball milled LiBH₄. The apparent activation energy (E_a) of hydrogen desorption had been reduced from 198.31 kJ mol⁻¹ for ball milled LiBH₄ to 155.8 kJ mol⁻¹ for 30 mol% h-BN doped LiBH₄. In addition, the rehydrogenation of the composite is achieved under 400 °C and 10 MPa of H₂. These remarkable results are largely attributed to the lone pair electrons of nitrogen induced destabilization of LiBH₄ and their heterogeneous nucleation.