Hydrogenation and dehydrogenation of two different phases in a multiphase Ti-V-based alloy Ti0.8Zr0.2V1.867Mn0.373Cr0.56Ni0.7, namely the C14 Laves phase with hexagonal structure and the V-based solid solution phase with body centered cubic (bcc) structure during electrochemical charging and discharging were investigated by X-ray powder diffraction (XRD) analysis. For the alloy investigated, the C14 Laves phase component, which had good surface electrochemical activity for decomposing water, was hydrogenated from the very beginning of the charging process and was providing hydrogen to both phase components throughout the entire electrochemical charging process. The V-based solid solution phase, which had no or very low surface electrochemical activity for decomposing water during electrochemical charging, could obtain hydrogen only from its neighboring C14 Laves phase component when the hydrogen content of which was high enough to build up an adequate pressure to feed hydrogen to its neighboring phase component. The V-based solid solution phase experienced a phase change when the hydrogen in it reached a definite level, namely from bcc to body centered tetragonal (bct) structure. Probably due to the high stability of bct hydride phase of the V-based solid solution phase, it did not revert back to the initial bcc structure during the electrochemical discharging process conducted in our experiment at the room temperature and atmospheric pressure.

This paper describes the effects of treating the alloy powder of an electrode with 6 MKOH solution containingy M KBH4 (y=0.0, 0.005, 0.01, 0.02 and 0.03) on the kinetic properties of the electrode, including high rate dischargeablilty HRD, exchange current density I0, symmetry factor β, limiting current density IL, diffusion coeffcient of hydrogen in the a-phase Da, and electrochemical polarization ηe and concentration polarization ηc. The results show that the kinetic parameters HRD, 10, IL and Daincrease markedly with the increase in the concentration of KBH4, the ηe and ηc decrease rapidly with increasing concentration of KBH4, but the symmetry factor β does not change.

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.

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.