Effect of tin deposition over electrogenerated random defects on Pt(111) surfaces onto ethanol electrooxidation: Electrochemical and FTIR studies

In the present study, random superficial defects of the {110}-type were electrogenerated on an initially well-ordered Pt(111) single crystal electrode, by cycling the potential in the range from 0.05 to 1.30 V by 32 times in perchloric acid solution and in a scan rate of 0.05 V s−1, named as Pt(111)-32. After partial disordering of the electrode surface, it was modified by deposition of tin submonolayers in three different coverage degrees of Sn, namely, ѲSnDefects= 0.34, 0.54 and 1.0. The Sn is preferentially deposited on the {110}-type defects generated previously. The effect of tin over the electrocatalytic activity for the ethanol electrooxidation reaction (EOR) and CO oxidation was investigated by using cyclic voltammetry, while the mechanism of the alcohol oxidation on the unmodified and Sn-modified electrodes was investigated by using in situ Fourier Transform Infrared (FTIR) spectroscopy. The lower Sn coverage degree on defect sites (ѲSnDefects= 0.34) showed, in the first voltammetric cycle, very good performance for EOR, having a peak current at 0.58V twice the one observed for the unmodified Pt(111)-32 electrode. However, the situation changed in the second voltammetric cycle, where on the full Sn covered defect sites electrode (ѲSnDefects= 1) a better electrocatalytic response was observed with more tolerance to the strongly adsorbed blocking intermediate species at low potentials. Additionally, it was found that this behavior should be in part associated with the ability of this electrode decorated with Sn to oxidize CO at a lower potential than those observed for other surfaces. The production of CO2 and acetic acid is enhanced as the Sn coverage degree also increases, as shown by FTIR, however, the later product is the majority product of this reaction for all the investigated electrodes. Thus, the main effect of Sn is reflected in the increased production of acetic acid.