Effect of O 2 reduction on the coverage with CO ad at platinum in acid solution and reaction mechanisms

Abstract

The coverage of carbon monoxide on platinized platinum decreases only slightly during the reduction of molecular oxygen at 0.1, 0.2 and 0.3 V, while it disappears within the initial 500 s on smooth platinum in 0.5 M H 2SO 4 at room temperature. The removal of CO ad during the stirring of O 2 is due to intermediately formed hydrogen peroxide. The removal rate differs so much on smooth and platinized platinum because the total formation of H 2O 2, referred to the real surface area, is considerably larger on the smooth electrode than the platinized electrode. In contrast to the oxidation of molecular hydrogen, the reduction of molecular oxygen is not affected by CO ad on the platinized electrode. The O 2 reduction remains a predominant four-electron process in the presence of CO ad. The results are discussed in terms of different pathways for the O 2 reduction.