This thesis considers the electrochemistry of platinum-iridium electrodes in both sulphate- and chloride-containing electrolytes at 20 - 25°C. Both wire electrodes of appropriate alloy compositions and titanium-substrate electrodes were employed. Polarization curves were obtained, and a technique for measuring the surface area of the electrodes was employed in order to determine the effect of potentiostatic electrolysis on the electrochemically active area. The wire alloy electrodes showed polarization behaviour in 1M NaCl; pH 2 identical to that of platinum electrodes, indicating that iridium is not effective in reducing the passivation of these electrodes even with up to 25% alloy content. The coated electrodes showed irreversible surface area losses in both sulphate and chloride electrolytes, with the latter producing significant reductions after very short polarization times. It is suggested that oxidation of the substrate leading to electrical isolation of coating plates is responsible for the area decay. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate