Anodic Pretreatment Research Articles

The Effect of Electrode Pretreatment on the Oxygen Reduction on Platinum in Perchloric Acid

The effect of pretreatment of a platinum electrode on the electrochemical reduction of oxygen and of hydrogen peroxide in perchloric acid was studied at room temperature. Hydrogen and oxygen pretreatments affect the oxygen reduction in a manner similar to cathodic and anodic pretreatments, respectively. An interpretation of various electrode characteristics is given on the basis of this parallelism. Removal of strongly bound oxygen by hydrogen pretreatment or cathodization accelerates the decomposition of hydrogen peroxide and increases the open‐circuit potential and the rate of the oxygen reduction in solutions containing 10−5 to 10−7M peroxide. Decay rates from a high anodic potential provide a sensitive measure for peroxide concentrations in the electrolyte.

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

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