Abstract: The microstructures and electrode properties of Cr or Co-doped V_2.1TiNi_0.5Hf_0.05M_0.113 (M=Cr, Co) hydrogen storage alloys were investigated. It is found that all alloys consist of a main phase of V-based solid solution with b.c.c. structure and a secondary phase of C14-type Laves phase with a three-dimensional network structure. After the doping of Cr or Co into V_2.1TiNi_0.5Hf_0.05, the abundance and unit cell volume of the main phase decrease, and those of the secondary phase increase. The electrochemical measurements show that the discharge capacities of Cr-doped V_2.1TiNi_0.5Hf_0.05Cr_0.113 alloy and Co-doped V_2.1TiNi_0.5Hf_0.05Co_0.113 alloy are less than that of V_2.1TiNi_0.5Hf_0.05 alloy, but their cycle stability and high-rate dischargeability are improved markedly. The results show that Cr or Co doping into V_2.1TiNi_0.5Hf_0.05 alloy is significantly beneficial for the cycling stability.

Key words:  V-based hydrogen storage alloys; Cr doping; Co doping; electrode properties; microstructure