An in Situ FTIR Study of Ethanol Oxidation at Polycrystalline Platinum in 0.1 M KOH at 25 and 50 °C

Abstract

The electrochemical oxidation of ethanol at a polycrystalline Pt electrode was studied using insitu Fourier Transform InfraRed (FTIR) spectroscopy in 0.1M KOH at 25 °C and 50 °C. It was found that the equilibrium between Pt and reversibly-adsorbed OH shifts to favour the latter at 50 °C compared to 25 °C, and this was reflected in the higher oxidation currents observed in the voltammetry, as well as increased production of acetate in the FTIR spectra. Acetate is the only product observed at lower potentials. Above the transition potential, where at least some of the areas of the thin layer in the spectro-electrochemical cell become acidic, acetaldehyde, acetic acid and a small amount of CO 2 are produced. This transition potential depends strongly on temperature: -0.1V at 25 °C and -0.4V at 50 °C. The temperature dependence of the production of acetaldehyde and acetic acid strongly suggests that the rate determining step is the removal of the first proton from the initially-adsorbed ethoxide species, and we tentatively suggest that this is also the rds under alkaline conditions. Overall, our data provide additional support for the mechanism we have developed over a number of publications concerning the oxidation of small alcohols at polycrystalline Pt in alkaline electrolyte.

Ethanol Electro-oxidation on Palladium Revisited Using Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) and Density Functional Theory (DFT): Why Is It Difficult To Break the C–C Bond?

“…They report that, during the electro-oxidation reaction, ethanol is converted to acetate in alkaline pH while above the transition potential, i.e., under pseudo-acidic conditions, it yields acetic acid and trace amounts of CO 2 , as a result of the slow C−C bond splitting. 25 This is in agreement with the results from online mass spectrometry, evidencing CO 2 production over Pt and Pd in 0.01 M NaOH, where the formation of acetic acid is almost absent. 26 On Pd-based electrocatalysts, ethanol oxidation reactivity differs compared to Pt, which is illustrated most clearly under acidic conditions, where Pt yields mainly acetic acid and even some CO 2 , while Pd is completely inactive.…”

Spectroelectrochemistry, the future of visualizing electrode processes by hyphenating electrochemistry with spectroscopic techniques

“…A drawback of this method is that the exact thickness of the thin-layer is not as reproducible as with a fixed cell size, making the process of taking a background reference spectrum more difficult. The thickness of the layer can be calculated by measuring the absorbance of the bulk water vibration, 13 potassium ferricyanide, 14 or any other substance with a known concentration and molar attenuation coefficient and applying the Lambert-Beer law. This determination of the path length is not necessarily done using IR spectroscopy.…”

“…Several papers use the acronym SNIFTIRS, 14,37,[42][43][44] while other papers, seemingly using SNIFTIRS, don't make use of the term. 13,[45][46][47][48][49][50] SNIFITRS is a technique used for a number of different applications, such as the study of the oxidation of small organic molecules (such as ethanol and ethylene glycol) 13,45,48,49 and metal ions. 14,37,43 SNIFTIRS is also performed in combination with SEIRAS, for example for the studies of proteins.…”

“…[56][57][58][59] For a more in-depth description of SNIFTIRS and PM-IRRAS the authors recommend reading the work of Guidelli, 16 Bard 63 and Alkire et al 59 2.2.2.4 Electrode material and SEIRAS in reflection IR-SEC. Concerning SEIRAS in reflection IR-SEC, electrode materials used are Ni, 14,37,43 Pt, 13,[38][39][40][41]50,64 Pd 45,48,49 and Au. 46,47,62,65,66 While only Liu et al report on using the reflecting electrodes for surface enhanchement, 46,47 it is unlikely that the Au electrodes used by Hosseini et al, 62 Su et al 65 and Villalba et al 66 don't report any enhancement.…”

“…Recent applications of this cell included the analysis of p-benzoquinone, 253,257 2-diphenylaminothiophene based compounds 258 and a perfluoroalkylated fullerene. 259 In the last case, 19 F NMR spectroscopy was performed as opposed to the more common 1 H and 13 C experiments. The measurements in all of the applications just mentioned were performed over large timeframes of up to 17 hours of electrolysis with periodic NMR spectroscopy sampling.…”