Arguably, Pt(111) is the most studied platinum single crystal electrode. When compared to the other platinum surfaces, it is the most stable, with the lowest surface energy, and their surface atoms have the highest coordination number. Moreover, it is normally the surface structure modelled in DFT calculations, allowing to compare theoretical and experimental results for a better understanding of the electrocatalytic processes. However, when the electrochemical behavior of the Pt(111) electrode is studied, it has been found that it possesses properties that significantly differ from those observed for the rest of surfaces. The uniqueness of the behavior of the Pt(111) electrode will be reviewed in detail using experimental results supported by computational data. First, in absence of specific adsorption from electrolyte anions, hydrogen and OH adsorption processes take place in separate potential regions, giving rise to the appearance of a region between 0.35 and 0.6 V where no species is adsorbed on the surface. This important feature has allowed to experimentally determine the potential of zero free charge of the surface, which is of paramount importance when its activity to be rationalized. For the rest of basal planes, OH adsorption proceeds simultaneously with the final stages of hydrogen adsorption, and thus, the surface is either covered by Hads or OHads. Even steps or defect sites on any surface shows this dual behavior. This difference in the behavior between Pt(111) and the rest of surfaces is replicated when the electrocatalysis on platinum surfaces is studied. In fact, some experimental results obtained for the Pt(111) electrode are the result of the presence of defects on the surface. Thus, the oxidation of COads monolayer is initiated on the surface defects. Also, in an ideal Pt(111) surface, formic acid oxidation would proceed only through the active intermediate path and, CO formation would be restricted only to the presence of defect sites. A similar situation is observed when ethanol oxidation is studied, because the cleavage of the C—C bond only takes place on defects, and thus the products of ethanol oxidation on a perfect Pt(111) electrode would be acetic acid and acetaldehyde. In fact, it is the surface with the highest activity for this undesired path of the reaction.

Insights in the reactivity of Pt(111) electrodes

ACS Spring 2022

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