Ethanol, Acetaldehyde and Acetic Acid Adsorption/Electrooxidation on a Pt Thin Film Electrode under Continuous Electrolyte Flow: An in Situ ATR-FTIRS Flow Cell Study

The interaction of ethanol and its oxidative C2 derivatives acetaldehyde and acetic acid with a Pt thin film electrode in 0.5 M H2SO4 solution was investigated by in situ Fourier transform infrared spectroscopy in an attenuated total reflection configuration (ATR-FTIRS). Time-resolved spectro-electrochemical measurements were carried out under well-defined mass transport to/from the electrode in a thin-layer flow cell setup, allowing to in situ monitor the electrode vertical bar electrolyte interface and the formation/removal of adsorbed species in both potentiodynamic and potentiostatic mode. Spectro-electrochemical transients at constant electrode potentials upon electrolyte exchange were employed to identify adsorbed species and their temporal evolution, followed by subsequent stripping of the resulting adsorbates in the supporting electrolyte. Adsorption transient and stripping measurements performed at different constant potentials lead to the following conclusions. (i) Ethanol does not adsorb on Pt at potential below 0.15 V (RHE), whereas acetaldehyde decomposes to COad already at 0.06 V. Acetaldehyde decomposition proceeds via adsorbed acetyl species and the decomposition rate depends on the potential, having its maximum at 0.25 V-RHE and being slow at 0.06 V-RHE. (ii) At potentials between 0.3 and 0.5 V-RHE, both ethanol and acetaldehyde adsorption result in COad and adsorbed acetyl species coexisting on the Pt surface. (iii) Stable acetyl species adsorbed in the double layer region are decomposed to COad and CHx,ad fragments when scanning the potential into the H-upd region. (iv) At potentials where COad is oxidized to CO2 and the ethanol oxidation current is increased, adsorbed acetate is observed. The latter species are in a fast adsorption-desorption equilibrium with acetic acid in the solution.