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

Abstract

The interaction of ethanol and its oxidative C2 derivatives acetaldehyde and acetic acid with a Pt thin film electrode in 0.5 M H 2 SO 4 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|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 CO ad 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 CO ad and adsorbed acetyl species coexisting on the Pt surface. (iii) Stable acetyl species adsorbed in the double layer region are decomposed to CO ad and CH x,ad fragments when scanning the potential into the H upd region. (iv) At potentials where CO ad is oxidized to CO 2 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.

Electrochemical behaviour of gamma hydroxybutyric acid at a platinum electrode in acidic medium

“…The cathodic scan yields two main peaks: one corresponding to the reduction of the platinum oxides formed during the anodic scan and one inverted oxidation peak with an onset partially overlapping with the tail of the reduction peak associated to the oxidation of the hydroxyl group of the GHB. This behaviour is similar to the other alcohols as butanol and ethanol with mechanisms of oxidation reactions that are still object of studies on platinum and modified Pt electrodes [15,18,[23][24][25][26]. Also, the oxidation process is influenced by pH and GHB concentration, which can be potentially used for its identification and in sensor design.…”

“…The values obtained for GHB are much lower than these, which seems to indicate that the GHB oxidation occurs through a complex surface process where platinum hydroxides play an important role since has been described by several authors (16,17,(23)(24)(25)(26)). …”

Oxidation of ethanol on platinum nanoparticles: surface structure and aggregation effects in alkaline medium

“…Steps (3) and (4) represent the reaction steps that lead to the C-C bond scission necessary for achieving the complete oxidation to CO2, forming one-carbon fragments from ethanol or acetaldehyde [20,21]. Behm's group [22,23] have proposed acetyl species as the active intermediate for these CHX and one carbon oxygenated fragments, which is quickly transformed in CO through the reaction step (5). CO is strongly adsorbed on the Pt surface and hinders the electrocatalytic response of the electrode.…”

Coulometric Study of Ethanol Adsorption at a Polycrystalline Platinum Electrode

“…The rates of adsorption at 0.3 V over a wide range of ethanol concentrations exhibits a logarithmic dependence on adsorption time as is common for a heterogeneous surface (Elovich relationship). That leads to the conclusion that the adsorption at ~0.3 V is a relatively slow surface chemical process following the relatively rapid abstraction of a hydrogen atom, the latter proposed by Heinen et al (8). Rates of adsorption drop off steeply at potentials higher than ~0.4 V, where ethanol is oxidized to soluble products.…”

“…In recent years, a number of in situ spectroscopic techniques have been applied to the issue of composition. This includes the identification in the adlayer of adsorbed carbon monoxide (CO) (2-9), adsorbed acetaldehyde and acetyl (8)(9)(10)(11)(12)(13)(14)(15)(16), adsorbed acetate (17)(18)(19)(20), and adsorbed methyl group (CH x ) (21)(22). There is evidence for the existence of all of those species, besides acetate, at potentials below ~0.5 V and for adsorbed acetate at higher potentials.…”