Activation behavior of the Zr-based Laves phase alloy electrode

The poor activation of the Zr-based AB(2) Laves phase alloy hydride electro de is one of the problems retarding their commercialization. A surface trea tment technique was carried out here to improve the poor activation of the alloys Zr(V-0.1.Mn0.3Ni0.6)(2), Zr(V0.1Mn0.3Ni0.6Co0.05)(2), ZrTi0.1(V0.1Mn 0.3Ni0.6Co0.05)(2) and ZrTi0.1(V0.1Mn0.3Ni0.6C0.05Cr0.05)(2). We pre-treate d the alloy powders by immersing and stirring them in solution of NH4F/NiCl 2 to make the alloy surface clean and form st layer of nickel-rich, which h as been regarded as an indispensable factor for the electrochemical activit y 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 electr odes made from the treated alloy powder is over 345 mA h g(-1) at the disch arge current density of 100 mA g(-1). Especially, the alloy electrode of th e treated ZrTi0.1(V-0.1Mn0.3Ni0.6Co0.05Cr0.05)(2) gives a discharge capacit y 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 struct ure is a cubic AB(2) Laves phase. The different activation property of the alloy electrode was analyzed on the basis of surface examination by scannin g electron microscope (SEM), specific surface area (SSA) and X-ray photoele ctron spectroscopy (XPS). (C) 2001 Elsevier Science B.V. All rights reserve d.