Manipulation of electrocatalytic reaction pathways through surface chemistry: In situ Fourier transform infrared spectroscopic studies of 1,3-butanediol oxidation on a Pt surface modified with Sb and S adatoms
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Cyclic voltammetry and in situ Fourier transform infrared ( FTIR) spectroscopy were employed to study the electrocatalytic properties of a Pt electrode modified with adatoms of antimony (Sb) or sulfur ( S) for 1,3-butanediol (1,3-BD) oxidation. The results demonstrated the possibility of manipulating the reaction pathways involved in 1,3-BD oxidation through chemical modification of the Pt electrode surface. Both Sb and S adatoms (Sb-ad and S-ad) can inhibit the dissociative reaction of 1,3-BD into CO, which is the main source of self-poisoning in electrocatalysis of small organic molecules. On Pt electrodes modified with a high coverage of Sb-ad (Pt/Sb-ad) the onset oxidation potential of 1,3-BD has been significantly decreased, which is attributed to the fact that the oxidation of Sb-ad occurs at lower potentials than that of the Pt surface. In situ FTIR results illustrated that, although at potentials below 0.5 V ( vs a saturated calomel electrode), at which the Sb-ad is stable on the Pt electrode surface, both carbonyl and CO2 species have been observed, the principal oxidation products of 1,3-BD are carbonyl species. Such results indicate that the reaction is mainly the dehydrogenation of 1,3-BD molecules. However, at potentials above 0.5 V the proportion of CO2 species in the oxidation products increases quickly, implying that the reaction has turned to the breakage of C-C bonds in 1,3-BD molecules and the subsequent oxidation of the cleaved fragments. In contrast with the cases of 1,3-BD oxidation on Pt and Pt/Sb-ad electrodes, the reaction of 1,3-BD oxidation on a Pt electrode modified with S adatoms (Pt/S-ad) is oriented completely to the production of carbonyl species when electrode potentials are below 0.9 V, though the reaction activity is relatively low. When the electrode potential is increased above 0.9 V, the intensity of the CO2 IR band in the FTIR spectra increases rapidly, corresponding to a fast oxidation of 1,3-BD on surface Pt sites recovered by the oxidation and desorption of S-ad from the Pt surface.