Hydrogen Storage Properties of as-Cast La1-xSmxMgNi3.6 -Co0.4 (x = 0∼0.4) Alloys

Abstract

La 1- x Sm x MgNi 3.6 Co 0.4 ( x = 0∼0.4) alloys were prepared by a vacuum intermediate frequency induction furnace with a high purity helium gas as the protective atmosphere. The effects of partially substituting Sm for La on the phase structure, morphology and hydrogen storage properties of the alloys were investigated. The detections of XRD and SEM reveal that the as-cast alloys contain two phases, LaMgNi 4 and LaNi 5 . The hydrogen storage capacity (wt%) of the alloys decreases with increasing Sm content, namely 1.859, 1.707, 1.585, 1.578 and 1.471, corresponding the variation of x from 0 to 0.4. The P-C-T curves of the alloys show flat plateaus corresponding to the absorption/desorption pressure plateaus of the LaMgNi 4 hydride. Meanwhile, the enthalpy change (Δ H ) and entropy change (Δ S ) of the LaMgNi 4 hydrides for hydriding decrease from −40.37 kJ/mol ( x =0) to −26.99 kJ/mol ( x =0.4) and from −101.9 J·(mol/K) −1 ( x =0) to −77.56 J·(mol/K) −1 ( x = 0.4), respectively. The electrochemical measurement displays that the maximum discharge capacity of the alloy electrodes declines from 347 mAh/g to 270.5 mAh/g, which is similar to the trend of the gaseous hydrogen absorption capacity. On the contrary, the cycle stability of the as-cast alloys obviously improves with the Sm content increasing, which can be attributed to the facilitated corrosion resistance by Sm substituting.