The use of single crystal platinum electrodes allows studying oxygen adsorption on different model surfaces in contact with solutions containing non-adsorbing electrolytes that could otherwise interfere with the adsorption of oxygenated species. Among the three basal planes, Pt(111) exhibits a marked separation (double layer region) between the H adsorption zone, below 0.35 V/RHE, and the adsorption of OH, above 0.55 V/RHE, the butterfly region. However, in the other two basal planes, Pt(100) and Pt(110), OH adsorption always takes place in the low potential region, coupled with H desorption, well below the adsorption of further oxygenated species at potentials close to 0.9 V/RHE. The stepped surfaces vicinal to these two basal planes clearly would also be able to adsorb oxygen at low potentials that could participate as intermediate in electrocatalytic processes related to fuel cell reactions.<br/>When we consider stepped surfaces vicinal to Pt(111), the step contributions appear at 0.13 and 0.28 V/RHE for (110) and (100) steps, respectively. This means that the presence of steps appear in the region of H adsorption on the (111) terraces. Several experiments show that step and terraces have distinct local potentials of zero charge. This opens the possibility to consider that steps could adsorb oxygen in the region in which these voltammetric signals appear. In this respect, laser temperature jump experiments point out different transients for water adsorbed at the steps and terraces.<br/>In this communication, new experiments have been performed to point out the presence of oxygenated species on the steps, at potentials immediately after hydrogen desorption. This would explain why stepped surfaces are more reactive than the corresponding Pt(111) basal plane for some model electrocatalytic reactions.

Adsorption of oxygenated species on stepped surfaces vicinal to Pt(111)

ACS Spring 2022

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