Structure and electrochemical properties of composite electrodes synthesized by mechanical milling Ni-free TiMn 2-based alloy with La-based alloys

Abstract

In the present study, hydrogen storage composite electrodes were prepared by mechanical milling the powder mixtures of Ni-free Laves phase alloy Ti 0.9Zr 0.2Mn 1.5Cr 0.3V 0.3 (AB 2) with LaNi 3.8Mn 0.3Al 0.4Co 0.5 (AB 5) and La 0.7Mg 0.25Zr 0.05Ni 2.975Co 0.525 (AB 3.5), respectively. X-ray diffraction (XRD) measurements found that the basic phase structure (hexagonal C14) was still maintained in TiMn 2-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 TiMn 2-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 Ti 0.9Zr 0.2Mn 1.5Cr 0.3V 0.3 alloy electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (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.