Microstructures and electrochemical properties of Co-free AB 5-type hydrogen storage alloys through substitution of Ni by Fe

Abstract

The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloy LaNi 4.05− x Al 0.45Mn 0.5Fe x (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 CaCu 5 phase structure disclosed by XRD pattern. However, small amount of the La 2O 3 phase, observed from SEM photographs, exists on the matrix of all the alloys and when x = 0.5, some web-like LaNi 2.28 phase is segregated out along the crystal boundary.