Electrode properties and thermal stability of melt-spun amorphous Mg67Ni28Pd5 hydride

We have examined electrode properties and thermal stability of the melt-spun amorphous Mg67Ni28Pd5 alloy subjected to electrochemical hydrogen charge. The maximum discharge capacity obtained at 308 K reaches 411 Ah/kg. The result shows that the melt-spun amorphous Mg-Ni based alloy has good hydrogen discharge characteristics even at room temperature. In the cycle test of the electrochemical measurement, the discharge capacity increases significantly with increasing cycle number in contrast to the significant degradation of the discharge capacity with cycle number for mechanically alloyed Mg-Ni based amorphous alloys. The present electrochemical data also indicate the existence of the plateau-like stage with very small gradient in the discharge hydrogen-composition isotherm curve. Furthermore, the hydrogen-absorbed amorphous alloy crystallizes through two stages consisting of the first-stage precipitation of Mg2Ni, followed by the second-stage precipitation of Mg2NiH4. The completed temperature of crystallization for the hydrogen-absorbed alloy increases by 65 K as compared with the as-spun amorphous single phase alloy. It is thus concluded that the stability of the Mg-Ni based amorphous alloy against crystallization increases by absorbing hydrogen.