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

We have examined electrode properties and thermal stability of the melt-spu n amorphous Mg67Ni28Pd5 alloy subjected to electrochemical hydrogen charge. The maximum discharge capacity obtained at 308 K reaches 411 Ah/kg. The re sult shows that the melt-spun amorphous Mg-Ni based alloy has good hydrogen discharge characteristics even at room temperature. In the cycle test of t he electrochemical measurement, the discharge capacity increases significan tly 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 discha rge hydrogen-composition isotherm curve. Furthermore, the hydrogen-absorbed amorphous alloy crystallizes through two stages consisting of the first-st age precipitation of Mg2Ni, followed by the second-stage precipitation of M g2NiH4. The completed temperature of crystallization for the hydrogen-absor bed alloy increases by 65 K as compared with the as-spun amorphous single p hase alloy. It is thus concluded that the stability of the Mg-Ni based amor phous alloy against crystallization increases by absorbing hydrogen.