Date of Award

2000

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Engineering, Materials Science.

Supervisor

Norchwood, Derek O.,

Rights

info:eu-repo/semantics/openAccess

Abstract

The electrochemical characteristics of metal hydride electrodes made from either LaNi4.7Al0.3 or Mm0.95Ti 0.05Co0.45Mn0.35 alloys (Mm, mischmetal of rare earth elements) are examined in detail. With increasing number of charge/discharge cycles, the metal hydride alloy powders undergo micro-cracking into smaller particles, and thus the specific surface area of the electrode increases, which then influences the kinetic properties of the electrode reactions. The specific surface area increases with increasing number of charge/discharge cycles before reaching a constant value after about 30 cycles. Other parameters, such as the diffusion coefficient of hydrogen, exchange current density, limiting current density, symmetry factor, over-potential and resistance were found to be related to the specific surface area, varying with cycling and also reaching stable values after about 30 cycles. These parameters are all related to the electrochemical properties of metal hydride electrodes. The influences of charge/discharge cycling, hydrogen concentration (or depth of discharge) and temperature on the electrochemical behavior of metal hydride electrodes are discussed in detail. Addition of copper powders to the metal hydride electrodes was found to greatly improve the kinetic properties. Pd-coating of the MmNi 5-based alloy powders in the electrodes lead to a significant improvement in resistance to capacity decay. The polarization processes of the electrode reaction included ohmic polarization, activation polarization and concentration polarization. By measuring both the resistances and the over-potentials related to the different polarization processes, the rate-determining steps (RDS) of the metal hydride electrode reactions were determined at different discharge current densities. The thermodynamic and kinetic measurements showed that the LaNi4.7Al0.3-based alloy electrodes have much better kinetic properties (higher exchange current density, larger RDS change current density, larger electrode reaction rate constant, lower activation energy and better low temperature behavior), than the MmNi5-based alloy electrodes. However, the MmNi5-based alloy electrodes, have higher thermodynamic stability, better electrode reaction reversibility, stronger resistance to capacity decay, more readily become stabilized and have a lower cost than the LaNi4.7Al0.3-based alloy electrodes.Dept. of Mechanical, Automotive, and Materials Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2000 .H36. Source: Dissertation Abstracts International, Volume: 61-09, Section: B, page: 4922. Adviser: Derek O. Norchwood. Thesis (Ph.D.)--University of Windsor (Canada), 2000.

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