Über den elektrochemischen aufbau und abbau von sauerstoff- und wasserstoff-belegungen auf platin in wässriger lösung

Abstract

The chemisorbed oxygen and hydrogen layers formed on platinum by anodic and cathodic polarization respectively have been investigated by means of charging curves. In cathodic polarization of a platinum electrode in 1N sulphuric acid at low current densities (e.g. 25 μA/cm 2, the coverage of the platinum reaches only half a monolayer of hydrogen atoms even at steady-state hydropen evolution. In a following anodic polarization with low c.d. this chemisorbed hydrogen layer undergoes disintergation accompanied by a rise in potential. After a further increase of potential during which only charging of the double layer takes place, there follows chemisorption of oxygen which the gradually changes over to the formation of a surface oxide film, two to three monolayers thick. Finally film formation becomes so slow that oxygen evolution predominates. In a now following cathodic polarization, the surface oxide including part of the chemisorbed oxygen layer is reduced to hydroperoxide primarily. The remaining part of the chemisorbed oxygen is not reduced until chemisorption of hydrogen has already set in. As a result of the reduction of the oxide film a loosely packed layer of platinum atoms for some time; it rearranges gradually to the normal lattice. This appears to be the reason for the increased activity of platinum electrodes in partly cathodic redox reactions after anodic pre-treatment. The potentials, referred to a hydrogen electrode in the same solution, in the case of the anodic formation of the chemisorbed oxygen layer and the surface oxide film were 0·8 to 1·3 V. The corresponding potentials during the reduction of the chemisorbed oxyen and the oxide film were within a somewhat lower region, 0-1 V. The potential of the chemisorbtion of hydrogen was between 0.3 and 0 V, decreasing linearily with the fraction of coverage