Hydrogen production from solid reactions between MAlH_4 and NH_4Cl

摘要

Solid reactions between alkali aluminum hydrides (MAlH_4, M = Li or Na) and NH_4Cl (at mole ratio 1:1) at 170 ℃ were investigated quantitatively using temperature programmed reaction (TPR), thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The release of 3 mol of H_2 from per mole of MAlH_4 was measured, corresponding to 5.6 wt.% H_2 capacity for the NaAlH_4/NH_4Cl system and 6.6 wt.% for LiAlH_4/NH_4Cl, respectively. By ball milling of the precursor compounds prior to the mixing, the reaction proceeded fast and NH_3 production as the by-product could be avoided. The quick solid reactions may be attributed to the low melting temperatures of MAlH_4 and the exothermic nature of the reactions. The reaction mechanism was also discussed.