Abstract

Hydriding combustion synthesis (HCS) has been regarded as an innovative process to produce magnesium based hydrogen storage alloys. In the present paper, a Mg-Mg 2 Ni composite hydrogen storage alloy was prepared by the HCS process under moderate conditions. Phase composition, synthesis mechanism and hydrogen storage properties were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and pressure composition temperature (PCT). The results indicated that the HCS product was composed mainly of MgH 2 , Mg 2 NiH 4 and Mg 2 NiH 0 . 3 . A gas-solid reaction mechanism played an important role in the HCS process. The hydriding activity of the as synthesised product was very high so that it absorbed 4 . 61 mass% hydrogen in the first hydriding process without any activation treatment and the maximum hydrogen storage capacity achieved was 5 . 24 mass%. Moreover, the hydriding rate was excellent. For example, it could absorb .3 . 20 and 4 . 05 mass% hydrogen within 4 min in the first and forth hydriding/dehydriding cycle respectively. The relationships between the plateau pressure and temperature were: lgP(0 . 1 MPa)524250 . 5/Tz7 . 9635 (hydriding), lgP(0 . 1 MPa)5 24125 . 4/Tz7 . 6502 (dehydriding) for the lower plateau, and lgP(0 . 1 MPa)522894 . 6/Tz5 . 9656 (hydriding), lgP(0 . 1 MPa)523855 . 9/Tz7 . 3435 (dehydriding) for the higher plateau.