Effect of O2 reduction on the coverage with COad 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 H2SO4 at room temperature. The removal of COad during the stirring of O2 is due to intermediately formed hydrogen peroxide. The removal rate differs so much on smooth and platinized platinum because the total formation of H2O2, 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 COad on the platinized electrode. The O2 reduction remains a predominant four-electron process in the presence of COad. The results are discussed in terms of different pathways for the O2 reduction.