No abstract

The present investigation is aimed to study MmNi 5-type (Mm = Mischmetal) hydrogen storage alloys with composition, Mm 0•8 La 0•2 Ni 3•7 Al 0•38 Co 0•3 Mn 0•6−x Mo 0•02 Fe x (x = 0, 0•1, 0•2 and 0•3). The alloys are synthesized by radio-frequency induction melting. To study their electrochemical properties via measurements of discharge capacity, activation process, rate capability and cyclic stability, electrodes are fabricated using as-synthesized and annealed version of the alloys. The maximum discharge capacity is recorded as 288 mAhg −1 for the iron concentration, x = 0•1, as compared to 270 mAhg −1 for the alloy electrode without iron. Similarly, 99% cyclic stability is observed in annealed alloy electrode (x = 0•1) as compared to 78% in the alloy electrode without iron. Hence, small amount of iron-substitution (x = 0•1) in the alloy is found to improve the electrochemical properties. This improvement is thought to be due to less pulverization of the alloy in electrochemically-cycled alloy, as confirmed through structural and microstructural characterizations carried out by X-ray diffraction phase analysis and scanning electron microscopy of as-fabricated and electrochemically-cycled electrodes.