Activation behavior of the Zr-based Laves phase alloy electrode

Abstract

The poor activation of the Zr-based AB 2 Laves phase alloy hydride electrode is one of the problems retarding their commercialization. A surface treatment technique was carried out here to improve the poor activation of the alloys Zr(V 0.1 Mn 0.3Ni 0.6) 2, Zr(V 0.1Mn 0.3Ni 0.6Co 0.05) 2, ZrTi 0.1(V 0.1Mn 0.3Ni 0.6Co 0.05) 2 and ZrTi 0.1(V 0.1Mn 0.3Ni 0.6Co 0.05Cr 0.05) 2. We pre-treated the alloy powders by immersing and stirring them in solution of NH 4F/NiCl 2 to make the alloy surface clean and form a layer of nickel-rich, which has been regarded as an indispensable factor for the electrochemical activity of the alloy. It was found that the activation of the alloy electrode has been greatly improved by this method. The discharge capacity of the electrodes made from the treated alloy powder is over 345 mA h g −1 at the discharge current density of 100 mA g −1. Especially, the alloy electrode of the treated ZrTi 0.1(V 0.1Mn 0.3Ni 0.6Co 0.05Cr 0.05) 2 gives a discharge capacity of 390 mA h g −1 at the first cycle, however, the discharge capacity of the untreated alloy electrode is only 42 mA h g −1 at the first cycle. The analysis of X-ray diffraction (XRD) shows that the alloy of crystal structure is a cubic AB 2 Laves phase. The different activation property of the alloy electrode was analyzed on the basis of surface examination by scanning electron microscope (SEM), specific surface area (SSA) and X-ray photoelectron spectroscopy (XPS).