Structural, Electrochemical and Hydrogen Sorption Studies of Nanocrystalline Ti-V-Co and Ti-V-Ni-Co Alloys Synthesized by Mechanical Alloying Method

M Balcerzak

doi:10.1007/s11665-019-04266-x

Abstract

In this paper, Ti-V-Co and Ti-V-Ni-Co alloys are considered as the hydrogen storage systems and the negative electrodes in Ni-MHx secondary batteries. This work shows results of studies that have been made on Ti0.5V1.5−xCox and Ti0.5V1.4−xNi0.1Cox nanocrystalline alloys (x = 0, 0.1 0.2, 0.3) synthesized by the mechanical alloying technique. The goal of this study is to determine an effect of partial replacement of V by Co atoms on hydrogen storage and electrochemical properties of Ti-V and Ti-V-Ni alloys. X-ray diffraction studies have proven that 14 h of the ball milling has resulted in crystallization of body-centered-cubic solid solution. Studies performed on high-resolution transmission electron microscope confirm creation of nanocrystalline materials. Hydrogen sorption/desorption measurements that have been performed at 303 K show that Co accelerates the hydrogen sorption process, diminishes hysteresis and ameliorates the hydrogen storage reversibility. Properties of Ti-V-Co alloys, described in this work, originate mainly from structure of these materials. Electrochemical measurements of Ti-V-Co alloys have shown these materials poorly absorb hydrogen in 6 M KOH solution. Ti0.5V1.4−xNi0.1Cox alloys are characterized by better activation properties and improved cyclability in comparison to Co-free Ti0.5V1.4Ni0.1 alloy.

Highlights

Body-centered-cubic (BCC) solid solutions have been studied for more than twenty years according to their possible usage as the hydrogen storage system and the secondary battery materials
The highest discharge capacity obtained for Ti-V-Co alloys did not exceed 20 mAh gÀ1, which indicates that these solid solutions are unsuitable for Ni-MHx negative electrodes
Hydrogenation/dehydrogenation and electrochemical properties of BCC alloys were studied in this work

Summary

Introduction

Body-centered-cubic (BCC) solid solutions have been studied for more than twenty years according to their possible usage as the hydrogen storage system and the secondary battery materials. As a result of implementation of these methods, alloys that are characterized by microcrystalline structure are synthesized (Ref [1,2,3]). I have recently synthesized V-rich BCC solid solutions through the mechanical alloying (MA) (Ref 4). The effect of use of MA method was the creation of the nanocrystalline BCC alloy which absorbed 3.67 wt.% of hydrogen at near room temperature. It resulted from the fact that V-rich BCC solid solution hydride phase was too stable to desorb hydrogen in moderate conditions. The usage of Vrich alloys is limited due to the fact that vanadium is an expensive element (Ref 4)

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