Effect of cobalt on the microstructure and hydrogen sorption performances of TiFe0.8Mn0.2 alloy

Abstract The microstructures and the hydrogen sorption performances of TiFe0.8Mn0.2Cox (x = 0, 0.05, 0.10, 0.15) and TiFe0.8Mn0.2-yCoy (y = 0.05, 0.10) alloys have been investigated. For TiFe0.8Mn0.2Cox alloys, the lattice parameters of TiFe phase decreased and the Laves phase contents increased with the addition of Co. With the increase of Co content in TiFe0.8Mn0.2Cox alloys, the maximum hydrogen storage capacities of TiFe0.8Mn0.2Co0.05 and TiFe0.8Mn0.2Co0.10 alloys decreased, but the effective hydrogen capacities increased, which is ascribed to the improved flatness of the α-β desorption plateau. Substitution of Co for Mn in TiFe0.8Mn0.2-yCoy alloys can effectively lead to single phase of TiFe alloys. Therefore, TiFe0.8Mn0.2-yCoy alloy showed a deteriorated activation property, but its effective hydrogen capacity increased remarkably due to the obviously improved flatness of the α-β desorption plateau. The addition of Co might adjust the change of the octahedral intersitial environment caused by Mn doping in TiFe phase, which contributes to the improved flatness of the α-β desorption plateau and hence the increased effective hydrogen capacity.