Microstructures and electrochemical properties of Co-free AB5-type hydrogen storage alloys through substitution of Ni by Fe

The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloy LaNi4.05−xAl0.45Mn0.5Fex (0 ≤ x ≤ 0.5) have been investigated with different additions of Fe in replacement of Ni. With the increase of Fe content the maximum discharge capacity gradually decreases from 334.8 mAh g−1 to 292.8 mAh g−1, however the cycle stability is improved correspondingly. The capacity decay can remain 28.6% (x = 0.5) after 300 charge/discharge cycles. The high rate discharge (HRD) ability of the alloys (x ≤ 0.5) is improved with the increase of Fe content. It is found that all of the alloys are single CaCu5 phase structure disclosed by XRD pattern. However, small amount of the La2O3 phase, observed from SEM photographs, exists on the matrix of all the alloys and when x = 0.5, some web-like LaNi2.28 phase is segregated out along the crystal boundary.