Effect of Ce element on hydrogen storage property of TiMn₂-based alloys

In this study, the effect of Ce content on the hydrogen storage property of Ti_0.98Zr_0.02Mn_1.5Cr_0.05V_0.43Fe_0.09Ce_x (x = 0, 0.02, 0.04, 0.06) alloys was investigated. The microstructure analysis indicated that all these alloys exhibited dendritic microstructures without segregation of chemical elements, and the dominant phase was identified to be the C14 Laves phase. After activation twice at 4 MPa and 473 K, these alloys exhibited excellent hydrogen absorption properties. The addition of Ce content significantly improved the kinetics of the alloys. Especially when the x = 0.02, the hydrogen absorption capacity reached 90% of its maximum capacity within 137 s at 293 K. The results of pressure-composition-temperature curves showed that with the increase of Ce content, the hydrogen absorption capacity increased first and then decreased, reaching the maximum value of 1.84wt% when the x = 0.04. Thermodynamic results indicated that with the increase of Ce content, the enthalpy and entropy of hydrogen absorption also increased first and then decreased, which was consistent with the variation of hydrogen storage capacity. Thus, the improvement of the hydrogen absorption capacity by the addition of Ce was believed to be related to the increase of the enthalpy. The increasement of lattice constant of C14 Laves phase and the deoxidization effect of Ce were supposed to be beneficial for the improvement of the hydrogen absorption kinetics.