โ Scribed by P. Sidheswaran; Hira Lal
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The kinetics of anodic oxidation of chemisorbed methanol, formaldehyde, formic acid and reduced carbon dioxide on platinum have been reported in previous communications 1-3 from this laboratory. Of particular interest is the inhibitive action of chloride ions on the rate of the reactionl'3'4; this contrasts with the rather small effect of irreversibly adsorbed iodide ions 2.
For a further insight into the mechanism of the reaction, it is of interest to investigate the influence of anion specific adsorption on the energy of activation of the anodic oxidation process. The data available are meagre and pertain only to acid sulfate solutions 5'6. Breiter 5 has made a comparative study of the effect of temperature on the anodic oxidation of chemisorbed methanol, carbon monoxide and reduced carbon dioxide in the temperature range 1-60ยฐC. He has reported significant differences in the potential of oxidation of these species at temperatures removed from room temperature. The activation energy for the oxidation of chemisorbed methanol was found to be much smaller than that for carbon monoxide and reduced carbon dioxide indicating that the chemisorbed organic species involved are different in the two cases.
The present studies relate largely to the anodic oxidation of chemisorbed methanol and formaldehyde layers in acid sulfate and acid chloride solutions. The choice of methanol and formaldehyde films is based on the fact that their nature is better understood than is the case with other chemisorbed species. Thus, for example, there is considerable evidence that the dissociative adsorption of methanol and formaldehyde on platinum in acid sulfate solutions results in the species HCO 4'7-10 and CO 3, respectively. In acid chloride solutions, on the other hand, the chemisorbed species largely correspond to the composition HCO 3.
The platinum sheet electrode, 2 ร 1 cm, was platinized from 1 ~ H2PtC16 at 2 mA cm-2 for 3 h, and allowed to age for several months before use. The roughness factor as determined from the hydrogen region of the charging curve was in the range 500-600.
The cell was an all-glass unit which permitted operations to be performed out of contact with air. Measurements were made in an air-conditioned room maintained at 26 + 1 ยฐ C. For measurements at other temperatures in the range 4-80 ยฐ C, water at
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The rate of removal of oxide films from pIatinized platinum electrodes immersed in 1 M phosphoric acid containing various reducing agents was investigated using cathodic stripping techniques to determine the amounts of oxide remaining on the surface after various periods of reaction. The order of re