Hydrogen desorption kinetics of the destabilized LiBH4[sbnd]AlH3 composites

Abstract

LiBH4 can be destabilized by AlH3 addition. In this work, the hydrogen desorption kinetics of the destabilized LiBH4AlH3 composites were investigated. Isothermal hydrogen desorption studies show that the LiBH4 + 0.5AlH3 composite releases about 11.0 wt% of hydrogen at 450 °C for 6 h and behaves better kinetic properties than either the pure LiBH4 or the LiBH4 + 0.5Al composite. The apparent activation energy for the LiBH4 decomposition in the LiBH4 + 0.5AlH3 composite estimated by Kissinger's method is remarkably lowered to 122.0 kJ mol−1 compared with the pure LiBH4 (169.8 kJ mol−1). Besides, AlH3 also improves the reversibility of LiBH4 in the LiBH4 + 0.5AlH3 composite. For the LiBH4 + xAlH3 (x = 0.5, 1.0, 2.0) composites, the decomposition kinetics of LiBH4 are enhanced as the AlH3 content increases. The sample LiBH4 + 2.0AlH3 can release 82% of the hydrogen capacity of LiBH4 in 29 min at 450 °C, while only 67% is obtained for the LiBH4 + 0.5AlH3 composite in 110 min. Johnson−Mehl−Avrami (JMA) kinetic studies indicate that the reaction LiBH4 + Al → ‘LiAlB’ + AlB2 + H2 is controlled by the precipitation and subsequently growth of AlB2 and LiAlB compounds with an increasing nucleation rate.