REVERSIBLE AGING OF IRIDIUM OXIDE ELECTRODES IN ACIDIC SOLUTIONS

The cyclic voltammetric response of iridium oxide films, grown electrochemically in acidic solutions, can display a notable dependence on the time spent in the reduced state and on other factors such as the carrying out of very slow sweep rate experiments. This is seen primarily as a substantial positive shift of the anodic peaks and in a diminishment, by up to about 50%, in the reaction kinetics. This effect, termed as film ageing, can be reversed, either by long times of cycling over an extended range of potential or by a brief holding period in the oxidized state of the film. Oxide films do not exhibit ageing in alkaline solutions. It is, therefore, suggested that film ageing is associated primarily with the loss of water from the film in acidic solutions at negative potentials, resulting in the inhibition of subsequent ion/solvent transport processes in the film.