Platinum Metals Rev., 1958, 2, (1), 15
Oxide Films on Platinum Electrodes
Platinum, equally with gold, serves to typify the ideal of a noble metal. It neither rusts nor tarnishes in air whether it is kept for centuries in industrial or marine atmospheres or in clean country air, or whether it is heated in air to high temperatures for long periods. In all these conditions, it is normally considered that a platinum surface will remain clean and bright and free from any tendency to scale, tarnish or develop protective surface oxide films as do the base metals.
Similarly, a platinum anode is commonly considered to present always a clean metallic surface to the electrolyte in which it is immersed, so that electrons can pass freely between the metal and the liquid unimpeded by any oxide barrier.
However, when the conditions at the anode are strongly oxidising, a platinum electrode sometimes behaves as if it were protected by “a film of platinum oxide, which prevents more than superficial oxidation of the platinum and yet permits electron transfer processes”. In a recent contribution from the Department of Chemistry at Harvard University (J. Amer. Chem. Soc., 1957, 79 (18), 4901–4904), F. C. Anson and J. J. Lingane have provided some most convincing evidence that such films really exist. They have succeeded in stripping the films chemically from oxidised anodes and in determining their weight and composition. The films are comprised of PtO and PtO2 in a molar ratio close to 6 to 1.
These data constitute the first direct chemical proof of the formation of platinum oxide films.