Improvement in high-temperature performance of Co-free high-Fe AB5-type hydrogen storage alloys

The effect of the iron content on the structural and electrochemical characteristics (20–60 °C) of the La0.78Ce0.22Ni3.73Mn0.30Al0.17FexCo0.8−x (x = 0, 0.2, 0.5, 0.8) hydrogen storage alloys has been investigated systematically. With increasing Fe content and temperature, the discharge capacity and high rate dischargeability deteriorates, but the difference among the four alloys almost disappears with temperature increases. However the cycling life and self-discharge characteristic improve, especially at high temperature (60 °C), the cycling stability increases from 7.1% of high-Co alloy to 44.1% of high-Fe alloy and the charge retention increases from 51.8% to 70.9% respectively. In addition, the high-temperature dischargeability and high-temperature recovery properties also improve when x = 0.8. Electrochemical kinetics, potentiodynamic polarization, inductively coupled plasma-atomic emission spectroscopy and scanning electron microscope analyses were conducted to investigate the surface corrosion of the alloys. The results demonstrated that the dissolution of Ni, Mn and Al can be suppressed significantly in virtue of the sacrifice of Fe content, leading to a good relative anti-corrosion ability of high-Fe alloy, and consequently, excellent cycling stability, charge retention and other high-temperature performance obtained.