Effects of substituting Co with Fe on the microstructures and electrochemical characteristics of the as-cast and quenched Mm(NiMnSiAl)4.3Co0.6−xFex (x = 0-0.6) electrode alloys

The microstructures of the rare-earth-based AB5-type Mm(NiMnSiAl)4.3Co0.6−xFex (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) hydrogen storage alloys were analysed by XRD, SEM and TEM, and electrochemical characteristics of the as-cast and quenched alloys were measured. The effects of substituting Co with Fe on microstructures and electrochemical characteristics of the as-cast and quenched alloys were investigated in detail. The obtained results show that the effects of substituting Co with Fe on the phase structures of the as-cast and quenched alloys are imperceptible, but its effects on electrochemical characteristics of the alloys are notable. The discharge capacities decrease, but the cycle lives of the alloys were improved with the increase of the amount of Fe substitution. Especially, substituting Co with Fe can significantly enhance the cycle lives of the as-quenched alloys, which is mainly attributed to the grain refinement caused by substituting Co with Fe.