Structure and electrochemical properties of composite electrodes synthesized by mechanical milling Ni-free TiMn2-based alloy with La-based alloys

In the present study, hydrogen storage composite electrodes were prepared by mechanical milling the powder mixtures of Ni-free Laves phase alloy Ti0.9Zr0.2Mn1.5Cr0.3V0.3 (AB(2)) with LaNi3.8Mn0.3Al0.4Co0.5 (AB(5)) and La0.7Mg0.25Zr0.05Ni2.975Co0.525 (AB(3.5)), respectively. X-ray diffraction (XRD) measurements found that the basic phase structure (hexagonal C14) was still maintained in TiMn2-based alloy after short-time mechanical milling with additional La-based alloys. The fine particles of La-based alloy were found dispersing over the bulk particle of TiMn2-based alloy by observations of scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The electrochemical studies showed that the additional La-based alloys greatly improved the discharge capacity of the composite electrode. The maximum discharge capacity reached 310.4 mAh/g and 314.0 mAh/g for AB(2)-10 wt.% AB(5) and AB(2)-10 wt.% AB(3.5) electrodes, respectively, which was much higher than the maximum 48.6 mAh/g of original Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltarnmetry (CV) measurements suggests that AB(3.5)-type alloy as a surface- modifier is beneficial to the decrease of the charge-transfer reaction resistance. The mechanical milling with AB(5)-type alloy was found improving the hydrogen diffusion in the bulk of the alloy from the results of anodic polarization measurement. (C) 2007 Elsevier B.V. All rights reserved