\Electrochemical and structural properties of metal hydride alloys prepared by high energy ball-milling\

Author(s)

Elki Cristina de Souza

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2006-04-27

Examining board members

Edson Antonio Ticianelli; Antonio Carlos Dias Angelo; Assis Vicente Benedetti; Fritz Cavalcante Huguenin; Ana Maria Rocco

• Advisor: Edson Antonio Ticianelli

Abstract

This work reports results of studies on the structure and electrochemical properties of hydrogen storage alloy electrodes, formed by Zr0,9Ti0,1Ni1,04Mn0,64V0,46 (AB2-type), prepared in arc furnace and processed by ball milling in the presence of Ni and/or LaNi4,7Sn0,3 powder additives. The Mg- Ni based alloys with and without incorporation of Ti and Pt, processed by mechanical alloying were also investigated. In this case, electrochemical deposition of palladium was carried out on the surface of Mg-Ni based alloy particles aiming at improving the alloy stability. The structure of all materials were characterized by energy dispersive X-ray (EDS) analyses, X-ray diffraction (XRD) and scanning electronic microscopy (SEM). X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) were also employed for this purpose. Electrochemical studies involved measurements of the electrode polarization along the charge/discharge cycles and also monitoring total discharge capacity as a function of the cycle number. Reaction kinetics were investigated by electrochemical impedance spectroscopy (EIS) measurements, conducted at different states of charge, temperatures and cycle numbers for the different metal hydride electrodes. It was found that the charge storage capacity increased very slowly along the initial charge/discharge cycles for the bare AB2 alloy, but a significant decrease of the activation time, due to a raise on the active area caused by the milling treatment was seen, independent of the additive nature. Electrochemical impedance showed similar reaction kinetics for different AB2 samples. The inclusion of small content of Pt in the Mg-Ni alloy leaded to a significant increase of the material stability for the charge/discharge cycles, probably because of a reduction in the corrosion processes. Consistently, the electrochemical coatings of Pd lead to a raise in the cycling stability of these alloys. (AU)