MAGNESIUM-BASED HYDROGEN STORAGE MATERIALS MODIFIED BY MECHANICAL ALLOYING

摘要

The effects of mechanical alloying on microstructure and electrochemical performance of a Mg- Ni-Y-Al hydrogen storage alloy in 6 M KOH solution were studied. The ball-milled powders were exam- ined by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffrac- tion (SED) and energy dispersion spectrometry (EDS). TEM and EDS results clearly reveal that the smaller nickel clusters or particles were well dispersed on the surface of larger magnesium alloy particles by mechanical grinding for 72 h. With an increase in milling time to 240 h, the nickel clusters or particles dis- appeared and a new monophase alloy with amorphous structure was formed. The electrochemical capacity of the modified material significantly increased with increasing milling time within 72 h and then dropped to nearly nil when the milling time reached 240 h. The capacity decay, however, was always improved with increasing grinding time. Further analysis and discussion were made based on d.c. polarization and a.c. impedance spectroscopy measurement results.