Effect of Fe substitution on first hydrogenation kinetics of TiFe-based hydrogen storage alloys after air exposure

This study investigated how Fe substitution with Ni, Co, Cu, Mn, and Cr affected the first hydrogenation behavior of air-exposed TiFe-based hydrogen storage alloys. The alloy ingots were crushed into powders and exposed to air for 1 h to analyze the first hydrogenation kinetics. Although Fe was substituted with up to 30% of Ni, Co, and Cu, the alloys had a single TiFe phase. In addition, the TiFe0·7Ni0·2Co0.1 and TiFe0·7Co0·2Ni0.1 alloys also had a single TiFe phase in spite of the simultaneous substitution. The composition of the oxide layer changed by the addition of Ni, Co, and Cu, but the alloys did not absorb hydrogen. In the TiFe0·8Mn0.2 and TiFe0·8Cr0.2 alloys, a dual-phase microstructure consisting of TiFe and Mn/Cr-rich C14 Laves phase was formed, with a larger amount in TiFe0·8Cr0.2. Both samples absorbed hydrogen after air exposure without any thermal activation process. Comparing the first hydrogenation kinetics, TiFe0·8Cr0.2 had a shorter incubation time and faster hydrogen absorption rate than TiFe0·8Mn0.2.