Passivating effect of chemisorbed oxygen on the anodic oxidation of molecular hydrogen at platinum

Abstract

The oxygen coverage was determined by cathodic charging curves at different potentials under the conditions of periodic, low-speed, potentiostatic current potential curves in 1 N HClO4, with vigorous hydrogen or argon stirring between +0·6Vand +1·5V. In the case of hydrogen stirring the net current is practically due to the anodic oxidation of molecular hydrogen in the potential range of passivation. Fick's law is applicable to the hydrogen diffusion between + 0·8 V and + 1·1 V daring the anodic sweep. The decrease of the concentration of molecular hydrogen in the diffusion layer can be corrected for. The correlation between reaction rate and oxygen coverage shows that most of the passivation is caused by a small oxygen coverage (10 per cent). After the very active centres for hydrogen oxidation have been covered by oxygen, the inhibition increases little with potential above + 1·1 V during the anodic sweep.