T. Iwasita

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.

Structural effects and reactivity in methanol oxidation on polycrystalline and single crystal platinum

The electrooxidation of methanol on single crystal surfaces is characterized by the formation of strongly adsorbed intermediates. The splitting off of hydrogen atoms is superimposed on hydrogen desorption and gives rise to a well defined peak at polycrystalline and at Pt(100). The role of hydrogen as inhibitor of methanol adsorption is confirmed once more. Adsorbed CO and other hydrogenated adsorbed species like COH, HCOH and H2COH are detected by means of in situ FTIR spectra. The differential adsorption behavior of the three basal planes is emphasized by both the first scan of the respective voltammograms and the ir spectroscopy results. Band center shifts of the CO adsorbate indicate island formation starting at the early stages of adsorption. The band shift can be addressed mainly to chemical coupling between adsorbed CO species. The onset potential for bulk oxidation increases in the order Pt(111) < Pt(110) < Pt(100). While the main reaction pathway for methanol oxidation to CO2 involves adsorbed CO species, a second pathway seems to occur via intermediate formation of formic acid which causes adsorption bands at 1710, 1430 and 1230cm−1.

A sniftirs study of ethanol oxidation on platinum

The oxidation of ethanol at a platinum electrode in perchloric acid solution is followed by in situir reflection-absorption spectroscopy at constant potentials. Depending on the electrode potential different infrared bands were detected and assigned. The faradaic efficiencies for the different products depend on ethanol concentration.

On the study of adsorbed species at platinum from methanol, formic acid and reduced carbon dioxide via in situ FT-ir spectroscopy

Three different coordinated forms of CO adsorbed to the platinum surface were observed for methanol, formic acid and reduced carbon dioxide: linear-, bridge- and multi-bonded CO. Using a new experimental approach absolute absorption bands are observed for the adsorption of methanol and reduced carbon dioxide. Sample spectra are computed with respect to a reference spectrum which is taken before adsorption. In this way the presence of a COH adsorbate is demonstrated. The absolute band procedure must be applied to observe features exhibiting only a small dependence on potential, because in this case using the usual SNIFT-irS procedure (first adsorption and then collection of spectra at two potentials) the signals may cancel out when computing the difference spectra. Using Pt/Ru as a bifunctional catalyst for water splitting and CO/COH oxidation, surface poisoning during the oxidation of methanol is strongly diminished: current-potential relationships of technical interest are obtained.

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 adsorbed sulfate on Pt(111)

The absorption of sulfate species was studied on well ordered Pt(111) surfaces at pH 2.8 and 0.23 using in situ external reflectance ir spectroscopy. Independently of the pH in the solution the spectra present two overlapped vibrational bands. A strong one is located at 1220–1280 cm−1 and is potential dependent. The second one is observed as a shoulder at 1190 cm−1. The analysis using group theory and the surface selection rule shows that only sulfate ions are adsorbed at both pH, suggesting a strong Lewis acid character of the Pt(111) surface. The randomly distributed sulfate species are relatively tightly adsorbed and present weak lateral interaction. At increasing coverage the sulfate adlayer becomes more organized, as attested by the observed band narrowing. The maximum adsorption is observed at 0.8 V vs. Pd/H2 ie at potentials higher than that of the so called anomalous states in the voltammogram. A quadratic dependence of the applied electric field on the SO vibrational band of adsorbed sulfate is observed, suggesting a second order Stark effect.

Identification of methanol adsorbates on platinum: An in situ FT-IR investigation

In the present work we use a different experimental approach to study the products of methanol adsorption, namely, to adsorb under thin layer conditions. This procedure allows us to compute spectra showing absolute bands.

Identification of the adsorbate during methanol oxidation

Abstract The formation and oxidation of the methanol adsorbate at platinum in acid solutions is performed under potential control using a flow cell technique. The charges in both processes are equal; this fact confirms the results of Podlovchenko et al. obtained from charging curves after open circuit adsorption. It is shown, using the on-line MS technique and labelled methanol, CD 3 OH, that the adsorbed intermediate is probably COH.

Direct proof of the hydrogen in the methanol adsorbate at platinum — an ECTDMS study☆

The strongly adsorbed intermediate of methanol oxidation at platinum in H2SO4 solution is studied by Electrochemical Thermal Desorption Mass Spectroscopy (ECTDMS). Electrodes with adsorbates are transferred to UHV and exposed to TDMS. The presence of hydrogen in the adsorbate is shown directly. For comparison, the same experiments have been performed with HCOOH and CO.

Electrocatalysis of methanol oxidation by adsorbed tin on platinum

Abstract On line mass spectroscopy has been used to study the interactions between adsorbed tin and methanol adsorbate on Pt electrodes. The technique demonstrates clearly that tin catalyses effectively the reaction step involving strongly adsorbed intermediates. The oxidation state of adsorbed tin species as a function of potential has been calculated by measuring the charge during the injection of Sn(IV) and Sn(II) solutions. The role of ionic forms of adsorbed tin in the observed catalytic effect is discussed.