| Abstract
| - Electrochemical measurements and in situ scanning tunneling microscopy (STM) are performed toestablish a structure−reactivity correlation for peroxide or dioxygen reduction on underpotentially deposited(upd) Tl on Au(111) in 0.1 M HClO4. At the potential of catalytic activity toward the O2 reduction, STMreveals the presence of Tl islands on the Au(111) terrace with height of 0.24 ± 0.03 nm. These islandsexpand in size and number, as the potential becomes more negative, but the full Tl monolayer formed at−0.2 V vs NHE is catalytically inactive. Ethanethiol (EtSH) significantly inhibits the H2O2 reduction, andthe kinetics and thermodynamics of EtSH adsorption on the Tl upd are quantitatively analyzed. STMshows that EtSH introduction leads to the formation of a 0.15 nm high terrace along the edges of the Tlislands. This terrace is assigned to EtSH bound to the Au surface near the Tl islands with the alkyl chainoriented roughly perpendicular to the surface. These results show that edge sites around the Tl island arethe active site of catalytic O2 reduction by Tl upd on Au(111).
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