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Electrocatalysis of Underpotential Deposited Tin-Adatoms-Modified Gold Electrodes Toward Oxygen Reduction Reaction in Acidic Media

In the present article, underpotential deposition (UPD) of tin (Sn) onto a polycrystalline gold [Au (poly)] electrode in 0.5 M H 2 SO 4 solution containing 1.0 mM SnSO 4 is addressed. The in situ modified electrode with Sn-adatoms was utilized for the oxygen reduction reaction (ORR). The results demonstrate that the ORR is inhibited at low overpotentials in the presence of adsorbed Sn species while the concurrent UPD of Sn-adatoms in the high overpotential region drives the ORR through a mainly four-electron pathway, compared to a mainly two-electron one in the absence of Sn species. Hydrogen peroxide (H 2 O 2 ) also undergoes the electrocatalytic reduction at the modified electrode at the same potential as the ORR. A probable origin of the electrocatalytic activity of the Sn-adatoms-modified Au (poly) electrode is discussed based on the increased electronic interaction of O 2 molecules with the Sn-adatoms. The reaction was investigated using cyclic voltammetric, amperometric and hydrodynamic voltammetric techniques.