Structural and electrochemical characteristics of V2.1TiNi0.5Hf0.05M0.152 (MÂ =Â Co, Cr) hydrogen storage electrode alloys

The structural and electrochemical characteristics of V2.1TiNi0.5Hf0.05M0.152 (M = Co, Cr) hydrogen storage electrode alloys have been investigated. It is found that all the alloys consist of two phases indexed as a main phase of V-based solid solution with a bcc structure and a secondary phase of C14-type Laves phase. The addition of Co or Cr into the V2.1TiNi0.5Hf0.05 alloy decreases the amount of the main phase and increases the amount of the secondary phase. After adding Co or Cr into the V2.1TiNi0.5Hf0.05 alloy, the unit cell of the main phase contracts and that of the secondary phase expands. Electrochemical measurements show that the maximum discharge capacities of the Co- and Cr-added alloys are much less than those of the V2.1TiNi0.5Hf0.05 alloy, but their cycle stability and high-rate dischargeability are markedly improved. The results show that the addition of Co or Cr into the V2.1TiNi0.5Hf0.05 alloy is very helpful in improving the cycling stability.