A study of the chronopotentiometric reductions of oxygen and hydrogen peroxide at a palladium electrode

Abstract

The chronopotentiometric reductions of oxygen and hydrogen peroxide at a palladium cathode are profoundly affected by the chemical and physical state of the electrode surface. In alkaline medium, the reduction of oxygen produces a singlet 4-electron wave. In i M sulfuric or perchloric acid, the chronopotentiogram depends on the state of subdivision of the electrode surface. At an electrode on which a layer of finely divided palladium has been deposited by the reduction of an oxide film, a singlet 4-electron wave, or a well-developed doublet, is observed. As reaction with dissolved oxygen removes the finely divided metal from the electrode surface, the overpotential of the reduction increases, and the first wave of the doublet, originally enhanced by the disproportionation of some of the product hydrogen peroxide, approaches the theoretical transition time. The direct reaction of dissolved oxygen with palladium has been studied both in acidic and basic media. The dissolution of palladium by reaction with oxygen in acid medium, and the spontaneous formation of an oxide film in oxygen-saturated 1 M sodium hydroxide, both affect the electrode surface. A direct analysis of the oxidized film formed during anodization of palladium supplements previous qualitative studies by other authors and indicates the presence of two palladium oxides, the lower of which contains +2 palladium.