Open-circuit reduction of oxygen coverage on Pt by organic substances: II. Particular cases depending on the coverage degrees

Two particular cases of the open-circuit reduction of the oxygen coverage on Pt by organic substances are examined—at high and at low coverage degrees. Suitable expansion in series of the general equations of part I and some simplifications lead to linearized equations which can easily be verified experimentally. It is shown that the form of the initial section of the experimental curves (at high coverage degrees) can be explained either accepting a chemical reaction of the coverage with the organic substance or assuming that no chemical interaction proceeds and the form of the curve is determined by the double laye charing. The difference in the concentration dependences makes however these two mechanisms distinguishable. At low coverage degrees the experimental curves can be described accepting an electrochemical mechanism of reduction of the oxygen coverage with the adsorption of the organic substance as the rate determining step. The linearized equations derived allow the determination of the kinetic parameters of the process.