Kinetics of the Extended Growth of Anodic Oxide Films at Platinum in H 2 SO 4 Solution

The kinetics of growth of anodic oxide films at platinum in solution have been studied by in situ chronoellipsometry both under constant potential and under constant current mode of polarization. Two regions of growth can now be distinguished. In the first, the kinetics of growth satisfy the formalism of the Cabrera‐Mott model of high field assisted formation and migration of ions in the oxide phase, i.e. where is the potential difference across the oxide film and is the film thickness. In the first region, oxide growth is the only reaction that occurs at the electrode. Following this initial growth, which is already completed at a thickness of 4–6Å depending on the rate of growth, oxygen starts to evolve but the oxide film continues to grow though now with a reduced rate. The kinetics of growth in the second region are described by an equation of the form This equation for the extended growth of platinum oxide films is diametrically different from that which describes the initial growth. The complex nature of oxide growth at platinum is discussed in relation to the oxygen evolution reaction.