Platinum surface oxidation in the presence of different alcohols

The oxidation of organic molecules on platinum electrodes is directly associated to the presence of OH species on the surface. However, this is the same species that is oxidized to PtO form. Since it is difficult to study the organic molecule oxidation and Pt surface oxidation at the same time, it has been assumed that in there is no chance in the surface oxidation process in the presence of organic molecules. However, considering that both reactions depend on the same species, it is reasonable to believe that a competition must take place. In this way, the goal of this work was to investigate if the Pt surface oxidation is influenced in the presence of different alcohols. In order to analyze this theory, two different experiments were carried out in the absence and in the presence of different alcohols (methanol, ethanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol and glycerol). The first one was carried out with a Pt polycrystalline electrode and Pt reduction charge was used to investigate the surface oxidation extension during the positive going sweep. In order to avoid the alcohol oxidation current in the negative going sweep, the experiment was carried out in low alcohol concentration (10-2 molL-1) and with different scan rates to the positive (50 mVs-1) and negative (15 Vs-1) sweeps. In the second experiment, the defects created on Pt(111) electrode after cycling in the absence and presence of alcohol (10-1 molL-1) were used to measure the surface oxidation. Considering Pt(111) studies, it was observed that in the presence of alcohol molecules bigger than methanol, the formation of (110) defects is inhibited. The existence of vicinal hydroxyls seems to enhance this behavior. A relation between the end of alcohol oxidation (offset potential) and the disordering of the surface was observed. These results are in agreement with those obtained for Pt polycrystalline oxidation. From these experiments, it was possible to observe that the offset of the alcohol oxidation is inversely related to the number of Pt atoms oxidized. The surface oxidation extension in the presence of alcohols follows the order: methanol > 1,3-propanediol > ethanol > 1,2-propanediol > ethylene glycol > glycerol.