Yang Tai

Electrochemical and Hydrogen Absorption/Desorption Properties of Nanocrystalline Mg2Ni-type Alloys Prepared by Melt Spinning

Abstract The nanocrystalline Mg2Ni-type alloys with the compositions of Mg20Ni10−xCux (x=0, 1, 2, 3, 4) were synthesized by melt spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system, and their hydriding and dehydriding kinetics were measured by an automatically controlled Sieverts apparatus. The results show that all the as-spun alloys hold a typical nanocrystalline structure. The substitution of Cu for Ni improves the electrochemical hydrogen storage performances of the alloys significantly, involving both the discharge capacity and the electrochemical cycle stability. Furthermore, the hydrogen absorption capacity of the alloy first increases and then decreases with the rising of Cu content, but the hydrogen desorption capacity grows dramatically for the same reason.

Influence of Melt Spinning on the Electrochemical Hydrogen Storage Kinetics of RE-Mg-Ni-Based A2B7-Type Alloys

Abstract In order to improve the electrochemical characteristics of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M=Pr, Zr) for La has been performed. The melt spinning technology was used to prepare the La0.65M0.1Mg0.25Ni3.2Co0.2Al0.1 (M=Pr, Zr) electrode alloys. The influences of the melt spinning and substithting La with M (M=Pr, Zr) on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The results obtained by XRD and TEM reveal that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The as-spun (M=Pr) alloy displays an entire nanocrystalline structure, while an amorphous-like structure is detected in the as-spun (M=Zr) alloy, implying that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurement indicates that the high rate discharge ability (HRD) of the alloys first mounts up and then falls with rising of spinning rate. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics first increase and then decreases with growing of spinning rate.

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.

Hydrogen Storage Behaviour of Nanocrystalline and Amorphous Mg20Ni10-xCox (x=0~4) Alloys by Melt-Spinning

Abstract In order to improve the hydriding and dehydriding behaviour of the Mg 2 Ni-type alloys, Ni in the alloy was partially substituted by Co, and melt-spinning technology was used to prepare the Mg 20 Ni 10− x Co x ( x =0, 1, 2, 3, 4) hydrogen storage alloys. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The hydriding and dehydriding kinetics as well as the electrochemical performances of the alloys were measured. The results show that no amorphous phase is detected in the as-spun Co-free alloy, but the as-spun alloys substituted by Co display the presence of an amorphous phase. The substitution of Co for Ni and the melt spinning significantly improve the hydrogen absorption and desorption performances of the as-cast and spun alloys. Meanwhile, the substitution of Co for Ni enhances the discharge capacity and cycle stability of the as-spun alloys dramatically.