Studies on co-free rare-earth-based hydrogen storage alloys

A series of multi-component, Co-free Mm-based alloys were prepared. The effect of partial substitution of alloy components on the electrochemical properties was investigated. The results show that the electrochemical cycling stability is greatly improved by slightly raising the Al content in alloys and adding a small amount of Si and Cu. A satisfactory cycling stability is obtained with an alloy composition of MmNi 3.60Mn 0.36Al 0.54Cu 0.4Si 0.1. The replacement of Mm by a small amount of Ti or Zr is useful in improving the durability of alloys, but the rate capability decreases. The reason is discussed and explained by the EIS technique and consideration of the polarization resistance of electrodes.