Improved hydrogen storage reversibility of LiBH4 destabilized by Y(BH4)3 and YH3

Abstract

In the present study, the synthesis of two different LiBH4-Y(BH4)3 and LiBH4-YH3 composites was performed by mechanochemical processing of the 4LiBH4-YCl3 mixture and as-milled 4LiBH4-YCl3 plus 3LiH. The effect of in situ formation of Y(BH4)3 and YH3 on the hydrogen storage properties of LiBH4 showed that both systems are effective promoters but differ substantially from each other in terms of the dehydrogenation pathway. During LiBH4-Y(BH4)3 dehydriding, Y(BH4)3 decomposes first generating in situ freshly YH3 and subsequently, it destabilizes LiBH4 with the formation of minor amounts of YB4. About 20% of reversible hydrogen storage was obtained via the rehydriding of YB4-LiH at 400 °C and 6.5 MPa. As a novel result, the Y2/3(B12H12) compound was identified during dehydriding of Y(BH4)3. In the case of LiBH4-YH3 dehydrogenation, the increase of the hydrogen back pressure favors the formation of crystalline YB4, whereas a reduction to <0.1 MPa induces the formation of minor amounts of Li2B12H12. Although for hydrogen pressures > 0.1 MPa direct LiBH4 decomposition can occur, the main dehydriding pathway for LiBH4-YH3 composite yields YB4 and LiH. A combination of the composite nanostructuring reached by mechanochemistry and/or the presence of LiCl possibilities good hydrogen storage reversibility (about 80%) regardless of the hydrogen back pressure.