E. Pastor

A dems and FTir spectroscopic investigation of adsorbed ethanol on polycrystalline platinum

Abstract The nature of the strongly adsorbed species of ethanol is established using in situ FT ir spectroscopy. Bands in the C-H stretching region indicate the presence of CH 3 and CH 2 groups. The analysis of the band frequencies under consideration of the restrictions imposed by the surface selection rule, allows the assignment of the CH bands to an ethoxi species. Also, linear bonded CO and a species containing a COH group are observed. Results of DEMS experiments using isotope labelled ethanol ( 12 CH 13 3 CH 2 OH) discriminate between both carbon containing groups. DEMS data are used to calculate the percentage distribution of adsorbed species. Methane and ethane in the ratio 6:1 are produced during the reduction of the adsorbate at potentials below 0.25V vs. rhe . Oxidation of the adsorbed residues yields carbon dioxide as the only reaction product.

An FTIR study on the adsorption of acetate at the basal planes of platinum single-crystal electrodes

In-situ Fourier transform IR spectroscopy has been employed to study the adsorption of acetate on Pt(100), Pt(110) and Pt(111) electrodes. A characteristic band associated with the adsorbed acetate species is observed on all three surfaces near 1420 cm−1. This band corresponds to the CO symmetric stretching vibration of the COO group twofold coordinated to the surface. The potential dependence of the band intensity, band halfwidth and band center shift depend on the basal plane considered. The spectroscopic parameters are correlated with the shape of the voltammograms obtained with the respective surface in the acetate-containing solution.

Vibrational spectroscopy of carbonate adsorbed on Pt(111) and Pt(110) single-crystal electrodes

Abstract The adsorption of carbonate and bicarbonate ions on Pt(111) and Pt(110) has been studied using Fourier transform IR spectroscopy. At Pt(111) the spectral analysis provides evidence for the adsorption of one- and two-fold coordinated carbonate ions depending on the electrode potential. At Pt(110) only two-fold coordinated carbonate was detected. Bicarbonate ions are oriented at the Pt(111)|electrolyte interface, probably forming hydrogen bonds with adsorbed water. The potential dependence of the band centers is discussed in terms of the proposed adsorption model.

D/H exchange of ethanol at platinum electrodes

Abstract D/H exchange occurs during the electroreduction of ethanol at polycrystalline platinum. Methane and ethane presenting different degrees of D/H exchange were observed employing CD3CH2OH and CH3CD2OH. Using CH3CD2OH, total exchange takes place during the formation of ethane from both adsorbed and bulk ethanol. For the methyl labelled compound CD3CH2OH, a total exchange was observed during the production of methane from adsorbates, but only partially in the case of ethane. The results are consistent with the nature of the adsorbed residues of ethanol proposed in a recent publication. In situ Fourier Transform ir (FTir) analysis of the adsorption products confirms the isotope exchange reactions.

Structural effects on CO2 reduction at Pt single-crystal electrodes: Part 1. The Pt(110) surface

Abstract Cyclic voltammetry and Fourier transform IR spectroscopy have been employed to study the activity of Pt(110) single crystals towards CO 2 reduction. Linear-bonded CO and traces of multibonded CO are the main reaction products. No differences in the nature of “reduced CO 2 ” were observed for different adsorption potentials, adsorption times, base electrolyte composition and cooling conditions of the electrode surface. At any potential below 0.20 V the surface can be saturated, indicating that hydrogen readsorption takes place. Anionic carbonate species are adsorbed at potentials above 0.50 V.

Vibrational spectroscopy at the electrochemical interface

Abstract Results of in situ infrared investigations of the electrochemical interface using well defined metal surfaces are discussed. Spectral analysis on the adsorption of ions allow to establish the nature of the adsorbed species, the adsorption geometry and the interactions operating at the interface. This is demostrated for carbonate and sulfate ions adsorbed on the basal planes of Pt single crystal electrodes.

Progress in the study of electrocatalytic reactions of organic species

New results in the electrocatalysis of organic reactions based in the use of spectroscopic methods are presented. The methods and systems discussed are: (a) thermal desorption spectroscopy applied to the characterization of the metal—CO bond on Pt and PtRu alloys; (b) in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) used to establish the composition of adsorbed ethanol at platinum; and (c) DEMS applied to discriminte between bulk and adsorbate reactions during the oxidation of formic acid catalysed by adsorbed Pb at platinum. The possibility of a reaction pathway highlighting the role of water is suggested.

Spectroscopic investigations of C3 primary alcohols on platinum electrodes in acid solutions.: Part I. n-propanol

Abstract The electrochemical behavior of n-propanol (n-PrOH) on polycrystalline Pt in acid solutions was investigated using in situ Fourier transform infrared spectroscopy (FTIRS) and on line differential electrochemical mass spectrometry (DEMS). The main products of n-PrOH oxidation are CO2, propanal and propionic acid. Different types of adsorbates with one, two or three C atoms were detected. Ethane and propane are produced from n-PrOH adsorbates during potential cycling in the H-adatom potential region. An increase in the quantity of adsorbed CO was observed after hydrogenation of n-PrOH adsorbates.

Structural effects on CO2 reduction at Pt single-crystal electrodes: Part 3. Pt(100) and related surfaces

Abstract The reduction of CO2 at Pt(100) and some of its vicinal surfaces in the [0 1 1] zone has been studied in acid solutions. Voltammetric and in-situ Fourier transform IR (FTIR) spectroscope experiments reported in this paper suggest a complex role for the different surface features, (terraces, edges and randomly distributed defects) existing at a Pt(100) electrode. The well-ordered (100) terraces seem to be blocked during the first stage of the surface reaction by multibonded CO as demonstrated by FTIR spectroscope. The reduction reaction is enhanced by the presence of hydrogen adsorbed at defect sites, i.e. at potentials below 0.2 V. At the same time, defect sites give rise to the formation of linearly bonded CO to an extent directly related to its surface density. Finally, ordered (100) edge sites have been found not to be efficient for the formation of adsorbed species from reduced CO2.

Structural efects on CO2 reduction at Pt single-crystal electrodes: Part 2. Pt(111) and vicinal surfaces in the [011] zone

Well-ordered Pt(111) single-crystal electrodes are inactive towards CO2 reduction. Cycling the electrode in the Pt oxide region induces disorder on the surface, characterized by the presence of hydrogen adsorption states at 0.12 V and 0.26 V, which indicate the presence of domains with the geometry of (110) and (100) surfaces. In parallel with this, the electrode activity for CO2 reduction is increased. After interaction of CO2 with the perturbed Pt(111) surface, the suppression of the adsorption states corresponding to the defects indicates their important role in the electrode activity. The latter cannot be reached by simply introducing ordered (100) step rows on the (111) surface, as demonstrated by the limited activity of the vicinal Pt(211) and Pt(755) surfaces.