Microstructural feature and hydrogen storage properties of TiFe0.7Mn0.2X0.1 (X = V, Cr, Co, Ni, Cu) hydrogen storage alloy

This study investigated the microstructural features and hydrogen storage properties of TiFe-based quaternary alloys, where Fe in the TiFe 0 . 8 Mn 0.2 alloy was additionally substituted with the transition metals of V, Cr, Co, Ni, and Cu (TiFe 0 . 7 Mn 0.2 X 0.1 (X = V, Cr, Co, Ni, Cu)). The TiFe 0 . 8 Mn 0.2 alloy exhibited a dual-phase microstructure consisting of the B2 and C14 Laves phases. The substitution of Fe with V, Cr, and Ni increased the Laves phase percentage, while the formation of the Laves phase was suppressed in alloys with Co and Cu substitutions. In all the alloys, a small amount of the Ti 2 Fe phase was precipitated. The room-temperature activation properties of the alloys were evaluated. The TiFe 0 . 7 Mn 0 . 2 Cr 0.1 alloy, with the highest Laves phase percentage, exhibited the fastest first hydrogenation kinetics, while the kinetics slowed as the Laves phase percentage decreased. The TiFe 0 . 7 Mn 0 . 2 Co 0.1 and TiFe 0 . 7 Mn 0 . 2 Cu 0.1 alloys, which did not form the Laves phase, displayed slower kinetics; however, the room-temperature activation was still achievable due to the formation of the Ti 2 Fe phase. The hydrogen storage properties of the alloys were examined. The TiFe 0 . 7 Mn 0 . 2 V 0.1 and TiFe 0 . 7 Mn 0 . 2 Co 0.1 alloys exhibited similar hydrogen absorption and desorption behaviors to the TiFe 0 . 8 Mn 0.2 alloy, while the other alloys showed steeper plateau pressure slopes. The effective hydrogen storage capacities were evaluated under conditions of hydrogen absorption up to 10 bar at 30 °C and hydrogen desorption down to 2 bar at 70 °C. The TiFe 0 . 7 Mn 0 . 2 V 0 . 1 alloy exhibited a similar effective hydrogen storage capacity to the TiFe 0 . 8 Mn 0.2 alloy, whereas the storage capacity of the TiFe 0 . 7 Mn 0 . 2 Co 0.1 alloy was reduced. These analyses confirmed that substituting Fe with V in the TiFe 0 . 8 Mn 0.2 alloy enhanced first hydrogenation kinetics while maintaining excellent effective hydrogen storage capacity. • Microstructure and hydrogen storage properties of the TiFe 0·7 Mn 0.2 X 0.1 (X = V, Cr, Co, Ni, Cu) alloy were examined. • By substituting of Fe with V, Cr, and Ni, a dual-phase microstructure consisting of the B2 and Laves was formed. • The alloys substituted with Co and Cu did not form the Laves phase, resulting in slower first hydrogenation kinetics. • The alloys substituted with V and Co exhibited a plateau pressure slope similar to that of the TiFe 0·8 Mn 0.2 alloy. • The TiFe 0·7 Mn 0·2 V 0.1 alloy exhibited improved first hydrogenation kinetics and excellent hydrogen storage capacity.