Table of contents

Rechargeable aqueous lithium-air cells have been developed and manufactured with the objective of analysing the limitations of the technology. The barriers to the technology have been identified and solutions to some of them have been successfully demonstrated in this study.

A new type of zinc/air fuel cell comprising a Hg/Pb free Zn foam anode, a PVA/KOH electrolyte membrane and a MnO2/SiOC-based cathode was developed in this work. The electrochemical activity of the zinc foam and air electrode was investigated in 6 M KOH under half-cell conditions. The pristine ZnO layer of the foam matrix favoured direct oxidation of the zinc particles to zinc oxide in 6 M KOH. In the laboratory cell, a specific energy of about 500 mWh g-1zinc was measured at 5 mA discharging current with a zinc foam, a PVA/KOH/H2O membrane and a MnO2+Vulcan/carbon paper cathode. A correlation between cell performances and porosity of the zinc foam was found. However, stability of the Zn foam and SiOC GDL materials towards KOH should be improved.

An electrically rechargeable zinc-air cell was developed and demonstrated using a bi-electrode on the cathode side and a 3D zinc electrode. About 200 cycles corresponding to 5000h of operation was achieved with this configuration. An innovating hybrid bi-electrode was evaluated which significantly increase the energy efficiency of our system to about 70% with an energy density close to 110 wh/kg and also improves the power response of the zinc air battery for punctual power demand application.

Anomalous electrocrystallization of Zn in alkaline electrolytes is one of the hurdles hindering the development and commercialization of secondary alkaline Zn batteries. The issue stems from the fast electrochemical kinetics of Zn. Pulse deposition enables the use of high peak current densities and overpotentials in short periods of pulse on-time, increases the nucleation rate and improves the deposit morphology. Electrochemical behavior of Zn and effect of pulse parameters including duty cycle and frequency on deposit morphology was studied for electrolytes containing 4, 6 and 9 M KOH. It was shown that in order to attain fine-grain, smooth deposits, small duty cycles and high frequencies are required. Pulse deposition, however, does not improve the morphology in case highly concentrated KOH electrolytes are used.

Perovskite La0.6Ca0.4CoO3 powder was prepared through a sol-gel method and characterized by XRD and BET. The electrocatalytic properties of La0.6Ca0.4CoO3 (LCCO) and La0.6Ca0.4CoO3-Carbon composite (LCCO-C) based electrode layers towards oxygen reduction reaction (ORR) were studied using rotating ring-disk electrode technique (RRDE) in 1, 4, and 6 M KOH electrolytes. Koutechy-Levich theory and RRDE measurement were applied to acquire the overall electron transfer number and kinetic parameters, such as the kinetic currents and rate constants. The overall electron transfer number was measured to be almost 4 for both pure LCCO and composite LCCO-C. A synergetic effect toward the ORR was observed in the LCCO electrode layer in the presence of carbon. This synergetic effect might be one of the reasons for the improved ORR performance on the composite LCCO-C electrode.