Electrooxidation of 1-Propanol on Pt — Mechanistic Insights from a Spectro-Electrochemical Study using Isotope Labeling

A combination of in situ Fourier transform infrared spectroscopy in an attenuated total reflection configuration (ATR-FTIRS) and online differential electrochemical mass spectrometry (DEMS) was used to investigate the electrooxidation of 1-propanol on Pt film electrodes, focusing on the unambiguous confirmation of adsorbed propionyl as reaction intermediate and on its role in the adsorption/oxidation reaction. Using unlabeled and 13C-labeled 1-propanol, with the C1 atom being labeled, and employing mainly potentiostatic transient and adsorbate stripping experiments, we arrive at the following conclusions: (i) The shift of the band at 1640 cm–1, which was tentatively assigned to adsorbed propionyl, to 1610 cm–1 upon 13C-labeling confirms the above assignment. (ii) Adsorbed propionyl is the main precursor for COad formation, at least for COad from the carbon atom carrying the OH group (C1 atom). (iii) Upon dissociative adsorption of 1-propanol at 0.2 V, only the C1 carbon atom forms COad; further reaction of the alkyl chain as second propionyl decomposition product is inhibited. (iv) At 0.4 and 0.6 V, COad formation from the alkyl chain (12COad formation) is possible but proceeds more slowly than from the functional group. Mechanistic trends are summarized in a reaction scheme.