Investigations on hydrogen storage performances and mechanisms of as-cast TiFe0.8-mNi0.2Com (m=0, 0.03, 0.05 and 0.1) alloys

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In order to improve the hydrogen storage performances of TiFe-based alloys, a new type of TiFe0.8-mNi0.2Com (m = 0, 0.03, 0.05 and 0.1) alloys were prepared through vacuum medium-frequency induction melting. XPS results showed that the composition of surface oxide film contains TiO2, FeO and NiO for the cobalt-free alloy, and it also includes CoO and Co3O4 besides the above oxides for the cobalt-containing alloys. The activation temperature is 523, 403, 383 and 373 K for the TiFe0.8-mNi0.2Com (m = 0, 0.03, 0.05 and 0.1) alloys, respectively. The changes of the composition and microstructure of the surface oxide film are the root causes of the reduction of the activation temperature. XRD and SEM analyses showed that all the alloys are composed of the majority phase of TiFe phase and non-hydrogenated phase of Ti2Fe phase. Adding appropriate amount of cobalt is beneficial to inhibiting the generation of Ti2Fe phase and increasing the cell volume of TiFe phase. The hydrogenation capacity is proportional to the content of TiFe phase, which is 1.11, 1.48, 1.54 and 1.29 wt% for the TiFe0.8-mNi0.2Com (m = 0, 0.03, 0.05 and 0.1) alloys at 313 K, respectively. The hydrogenation plateau performance also is improved correspondingly.