L.X Chen

The electrochemical properties of LaxMg3-xNi9 (x=1.0-2.0) hydrogen storage alloys

Abstract LaxMg3−xNi9 (x=1.0–2.0) alloys were prepared by a powder sintering method and the influence of partial substitution of Mg by La on the crystal structure and electrochemical performance of the alloys was investigated. The ternary alloys with different La/Mg ratio are related to the hexagonal PuNi3-type structure. The increase of La/Mg ratio in the alloys leads to a linear increase of the unit cell volume. The La-rich alloys (x=1.8–2.0) show promising electrode properties including a large discharge capacity (∼400 mAh/g), easy activation and good high-rate dischargeability, although the cycling stability needs further improvement.

Influence of the material processing on the electrochemical properties of cobalt-free Ml(NiMnAlFe)5 alloy

Abstract Co-free MlNi 4.1 Mn 0.35 Al 0.3 Fe 0.25 (Ml: La-rich mischmetal) alloy samples were prepared in three different ways. The original as-cast alloy was prepared by vacuum levitation melting in a cold crucible. One-third of the as-cast ingot was annealed at 1273 K for 10 h, and another one-third was remelted and rapidly solidified by melt-spinning. The influence of the alloy preparation methods on their microstructure and electrochemical properties was studied. XRD and SEM results revealed that all of the three differently prepared alloys were of the single CaCu 5 -type structure phase, but their microstructure and electrochemical properties were changed markedly. The as-cast alloy had a typical dendrite structure with noticeable composition segregation and rather poor cycling endurance. While the annealed and melt-spun alloy were of an equiaxed structure and a very fine cellular structure, respectively, and had a more homogeneous composition and dramatically improved cycling endurance, although their activation rate and high-rate dischargeability were lowered somewhat. In this study, the melt-spun Co-free alloy showed the best cycling stability ( S 500 =69.2%) and a reasonably high capacity (305 mA h g −1 ) and 1C rate dischargeability (85.6%), which is attributed to its lower degree of pulverization and more uniform composition.

Electrochemical properties of Ml(NiCoMnCu)5 used as an alkaline fuel cell anode

Abstract The electrochemical properties of AB5-type rare earth–nickel multicomponent compounds Ml(NiCoMnCu)5 (Ml: La-rich mischmetal) used as an alkaline fuel cell anode were investigated at 30°C. A double-layer porous film structure with foamed nickel as current collector was adopted for the anode. A catalyst layer made of Ml(NiCoMnCu)5 alloy powder and a 60% aqueous suspension of polytetrafluoroethylene (PTFE) was on the electrolyte side, and a waterproof layer made of a Teflon aqueous suspension and Na2SO4 powder was on the gas side. The experimental results revealed that the anode performance strongly depends on the PTFE content of the catalyst layer, the thickness of the catalyst layer and the waterproof layer, and the cold compression pressure for electrode formation. When these four parameters were 12 wt.%, 0.25 mm, 0.2 mm and 12 MPa, respectively, the anode had a life-time of approximatly 550 h at a current density of 20 mA/cm2.

The phase structure and electrochemical properties of the melt-spun alloy Zr0.7Ti0.3Mn0.4V0.4Ni1.2

Abstract The crystal structure, phase abundance, microstructure and electrochemical properties of the AB 2 -type Laves phase hydrogen storage alloy Zr 0.7 Ti 0.3 Mn 0.4 V 0.4 Ni 1.2 were studied, prepared both by arc-melting and melt-spinning. The XRD patterns have revealed that two Laves phases, C14 and C15 are formed in the as-cast alloy. In the melt-spun alloy, besides the C14 and C15 phase in very fine crystal grains, there appears a new crystalline C14 phase with very fine crystallites, which is named the nanocrystallite C14 in this paper. SEM and EDS analyses have indicated that the microstructure of melt-spun alloy is a very fine dendritic structure (10×3 μm), while the as-cast alloy is a much coarser dendritic structure (300×50 μm) with noticeable composition segregation. Electrochemical tests have indicated that the melt-spun alloy has a higher discharge capacity of 385 mA h g −1 in comparison with 371 mA h g −1 for the as-cast alloy and the melt-spun alloy has very good cycling stability. After 500 cycles, 80.7% of the initial discharge capacity is retained, much higher than 63.1% of the as-cast alloy. It is thus inferred that the electrochemical capacity of the nanocrystallite C14 phase is higher than that of the conventional C14 phase. Nevertheless, the activation property and the high-rate dischargeability of the melt-spun alloy were both found to decrease noticeably, most probably due to the higher resistance against decrepitation and cracking of the alloy with a more refined grain structure.

Microstructure and electrochemical behavior of a rapidly solidified V3TiNi0.56Hf0.24Mn0.15Cr0.1 hydrogen storage alloy

Abstract The microstructure and electrochemical behavior of the rapidly solidified V3TiNi0.56Hf0.24Mn0.15Cr0.1 alloy were studied. It was found that the microstructure of the rapidly solidified alloy is composed of small dendrites except for the equiaxed grains near the ribbon surface. Compared with the induction-melted alloy, the rapidly solidified alloy has less of the C14-type secondary phase. The secondary phase is predominantly surrounded by the dendrite arms of the main phase in the rapidly solidified alloy. Furthermore, there is a lot of fine particles with diameters of 5–20 nm precipitated in the matrix of the main phase. Precisely because of these microstructures, the rapidly solidified alloy has a lower reversible capacity, a worse high-rate dischargeability and a slower activation rate than the induction-melted alloy. Even so, the cycle stability of the rapidly solidified alloy is improved.

Effects of the amount of Mg impurity on the electrochemical properties of Ml(NiCoMnTi)(5) hydrogen storage alloy

Conference Name:International Symposium on Metal-Hydrogen Systems, Fundamentals and Applications. Conference Address: ZHEJIANG, PEOPLES R CHINA. Time:OCT 04-09, 1998.