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.

A series of R3 (Fe, Mo) 29 (R=Ce, Nd, Sm, Gd and Y) intermetallic compounds with Nd3 (Fe, Ti) 29-type structure have been successfully prepared with suitable compositions and annealing conditions, these compounds are identified as the 3:29 type compound according to the x-ray diffraction patterns. The lattice parameters are determined, and the intrinsic magnetic properties Tc, Ms and Ba are reported.

The effective exchange coupling parameters JFeFe in the Fe sublattice and JRFe between the R and Fe sublattices have been calculated based on a mean field approximation according to the experimental values of the Curie temperatures of R3 (Fe, M) 29 (R=rare earth, M=V, Ti and Mo). JFeFe is largest when M=V and smallest when M=Mo, but JRFe is largest when M=Ti and smallest when M=Mo for the same R and different M in the R3 (Fe, M) 29 compounds.

In this paper, the electrochemical properties of MlNi4.3-xCoxA10.7electrode alloys, including high rate dischargeability, exchange current density 10, limiting current density IL, and diffusion coefficient of hydrogen in the hydride Da by means of linear polarization, anodic polarization, and electrochemical impedance spectroscopy were systematically studied. The results indicate that, with the increase of Co content, the cyclic stability is improved markedly, which agrees with previous investigation. However, activation becomes more difficult, and the high rate dischargeability decreases. The linear polarization and anodic polarization results suggest that the exchange 21 current density I0 and limiting current density IL decrease from the 395 (x=0) to 33mAg (x=1.3) and from 2263 (x=0) to 308mA g-1, respectively. The electrochemical impedance spectroscopy result also reveals that the diffusion coefficient of hydrogen in the alloys decreases rapidly with the increase in Co content in MlNi4.3-xCoxAl0.7 hydride alloy electrodes.

In this paper, the structural characterization of the ternary phase Y3 (Fe, Mo)29 compound has been investigated in great detail by refi+L43nement of the X-ray diffraction pattern. The structural relationship of the 3:29 phase with 2:17 and 1:12 phases has been studied according to theoretical calculations and experimental results. The results show that the 3:29 compound belongs to A2/m. space group and the 3:29 compound is a kind of mixed structure of 2:17 and 1:12 structures.