In our endeavor to improve the cyclic stability of La-Mg-Ni-Co type alloys, La0.7Mg0.3Ni2.652xMn0.1Co0.75Alx (x=0-0.5) hydrogen storage alloys were prepared and the structure and electrochemical properties of these alloys were investigated systematically. X-ray diffraction and Rietveld analyses revealed that the major phases are the (La, Mg) Ni3 phase and the LaNi5 phase. Electrochemical studies indicate that as Ni is progressively substituted by Al, the cyclic stability of alloy electrodes is noticeably improved due to the formation of a dense oxide film on the alloy surface. The capacity retention of the alloy electrodes for 100 cycles increases from 32.0% (x=0) to 73.8% (x=0.3). The maximum discharge capacity decreases with increasing Al content, and the high rate dischargeability, electrochemical impedance spectra, linear polarization, Tafel polarization, and potential-step studies all indicate that the electrochemical kinetics of the alloy electrodes is deteriorated. We ascribe this phenomenon to the increase of the charge-transfer resistance of the alloy electrodes and reduction of the diffusion rate of hydrogen from interior of the bulk to the surface due to the presence of the aforesaid Al-containing oxide film. The optimal content of Al in La0.7Mg0.3Ni2.652xMn0.1Co0.75Alx alloys in this study is in the range from 0.2 to 0.3.

A novel single phase R3 (Fe, M) 29 (R=Nd, Sm and Gd) compound series with M=Mo as a new stabilizing element has been synthesized. A systematic study of the formation and magnetic properties of R3 (Fe, Mo) 29 compounds has been performed. The lattice parameters and magnetic properties incIuding the Curie temperature Tc, saturation magnetization Ms and anisotropy field Ba at 300 and 4.2K are presented.

In this paper, the structural and electrochemical properties of La0.7Mg0.3 (Ni0.85Co0.15)x (x=2.5, 3.0, 3.5, 4.0, 4.5, 5.0) hydrogen storage alloy electrodes were studied systematically. X-ray diffraction Rietveld analyses show that all these alloys consist of a (La, Mg) Ni3 phase with the PuNi3-type rhombohedral structure and a LaNi5 phase with the CaCu5-type hexagonal structure. The (La, Mg) Ni3 phase abundance first increases to a high percentage (～75%) and then decreases with increasing x. In contrast, the LaNi5-phase abundance first remains low and almost unchanged and then increases to a high percentage (～70%) with increasing x. The pressure-composition isotherms shows that for each isotherm the plateau region widens and the plateau pressure is maintained almost unchanged when x increases from 2.5 to 3.5. However, as x increases further, the plateau region is shortened and becomes flatter, and the plateau pressure increases with x. Electrochemical studies indicate that all important electrochemical properties, including the maximum discharge capacity, the high rate dischargeability, the exchange current density, and the limiting current density of the alloy electrodes increase as x increases from 2.5 to 3.5 and then decrease when x increases further from 3.5 to 4.5.

A novel single-phase Y3 (Fe, Mo) 29 compound with Mo as a new stabilizing element has been synthesized with nominal composition Y1o.sFe86.7Mo2.8 via annealing at 1313K for three days, and then water quenching. The results of thermomagnetic analysis (TMA) show a magnetic ordering temperature of 376K. X-ray diffraction gives lattice parameters a=10.570 Å, b=8.508 Å, c=9.673 Å and β=96.98º. The temperature dependence of the magnetization Ms of Y10.5Fe86.7Mo2.8 in an applied magnetic field up to 7 T and the temperature dependence of the anisotropy field Ba are also reported.

The optimum compositions and annealing conditions of the preparing single-phase R3 (Fe, Mo) 29 (R=Tb and Dy) are reported. The structural characterization by X-ray powder diffraction provides evidence for a Nd3 (Fe, Ti) 29-type compound with the space group A2/m. The Curie temperatures Tc are 437 K for Tb3 (Fe, Mo) 29 and 408K for Dy3 (Fe, Mo) 29. The saturation magnetization Ms values are 77.5Am2/kg at 4.2K and 70.4Am2/kg at 300K for Tb3 (Fe, Mo) 29, and 73.0Am2/kg at 4.2K and 65.2Am2/kg at 300K for Dyz (Fe, Mo) 29.