Changes in hydrogen storage properties of binary mixtures of intermetallic compounds submitted to mechanical milling

Electrochemical loading of hydrogen in single and binary mixtures of the intermetallic compounds, TiNi, TiFe, Zr30Ni70 and Zr70Ni30 have been investigated after energetic mechanical milling. Enhanced hydrogen storage of the 50/50 (by weight) TiNi/ZrNi binary mixtures are only found after high energy milling (450 rpm for 12 h). The high energy milled 50/50 and 30/70 TiFe/Zr30Ni70 binary mixtures exhibited good electrochemical loading (~98 mA h g-1) at 25°C but this capacity was decreased by ~12% on increasing the temperature to 55°C. On the other hand, the 70/30 TiFe/Zr30Ni70 binary mixtures showed a 65% increase in the hydrogen capacity with temperature over the same range. High energy milling of the TiFe with carbon materials again led to a substantial increase in the storage capacity but here, this was attributed to a partial reduction of the surface oxides by the graphite /activated carbon. Thermal analysis of the samples using high pressure differential scanning calorimetry on the milled Zr70Ni30 sample showed a rapid deterioration of the hydrogen absorption /desorption features with thermal cycling over the range 100°C-310°C due to sintering of the samples.