Adsorption of acetic acid at platinum and gold electrodes: a combined infrared spectroscopic and radiotracer study

Abstract

The potential-dependent specific adsorption of acetic acid and acetate at polycrystalline platinum-and goldaqueous interfaces has been examined by potentialdifference infrared spectroscopy (PDIRS) in conjunction with quantitative surface concentration measurements using the radiotracer technique. Both the infrared and radiotracer measurements utilize a similar thin-layer solution arrangement. Extensive adsorption of acetic acid occurs at both platinum and gold, which increases at more positive potentials and reaches a maximum at the onset of anodic oxide formation. The PDIR spectra contain several features identified with solution acetic acid in the 1200-1800-~m-~ region, including vC4 and vC4 bands at 1710 and 1280 cm-I, respectively, arising from adsorption-induced changes in the thin-layer solution composition as well as a single band, at 1415 and 1400 cm-' on platinum and gold, respectively, due to adsorbed acetic acid. The intensity of the former bands can be employed to evaluate the extent of adsorption as a function of potential; the results are in semiquantitative agreement with the surface concentration-potential data from radiotracer measurements. Although the radiotracer measurements indicate that acetate is not significantly adsorbed, acetate solutions in unbuffered media also yield intense PDIR spectra at platinum and gold, the latter arising merely from pH-induced changes in the thin-layer solution composition associated with anodic oxide formation. The 1400-cm-' feature for adsorbed acetic acid is consistent with a symmetric carboxylate stretching mode; the absence of the corresponding asymmetric vibration is indicative of a C, geometry with both carboxylate oxygens oriented toward the metal surface. In view of the infrared spectra together with the observed absence of acetate adsorption, the most likely modes of acetic acid adsorption involve hydrogen bonding between the carbonyl oxygen and inner-layer water molecules, or by self-association to form dimers or chain structures. a grant (to A.W.) from Dow Chemical Corp. , 71-50-1; Pt, 7440-CHE-85-13732 to M.J.W.).The equivalent parallel conductance technique was used to study surfacestate behavior at the n-CdSe single crystal/aqueous sulfide interface. Surface states were found at -1.1 V versus SCE (-0.6 eV below the conduction band minimum) in solutions containing hydroxide and sulfide. The phase-sensitive photocurrent was affected by these states. Addition of dissolved sulfur to the solution removed the hump in the conductance versus voltage curves caused by these states and the photocurrent behavior is also improved.

In Situ FTIR Studies of an Oxidation Product from Protein Adsorption at the Platinum Electrode

“…These measurements were made to complement previous electrochemical studies made on the interfacial behavior of proteins and to confirm that oxidation of the protein accompanied by decarboxylation occurs at anodic potentials as proposed previously (1)(2)(3)(4)(5). This communication also follows successful experiments using the technique of subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) for the adsorption behavior of small organic molecules at Au(111) (6)(7)(8)(9). However, SNIFTIRS is used here to examine an oxidation product of an adsorbed protein at the platinum electrode.…”

In situ FTIR investigation of acetic acid electrooxidation on carbon supported Pt–Sn based trimetallic catalysts: Influence of the nature of the third metal

“…2d, 2g and 3g). Acetate species was observed at 1413-1420 cm −1 , which is related to the symmetric stretching of the COO group, S (CO 2 − ) [5,7,16]. According to Corrigan et al [7], the absence of asymmetric stretching of the COO group, as (CO 2 − ), expected around (1550-1600 cm −1 ), can be taken as proof that acetate adsorbate is oriented with the two carboxylate oxygen atoms toward to the surface.…”

“…In the SPAIR spectra, two positive-going bands at 1715-1727and 1383-1389 cm −1 are identical in form with that observed for the solution of acetic acid. These bands are assigned to the C O stretch ( C O ) and CH 3 bending mode (ı CH3 ), respectively [7,16,17]. The positive-going features of these bands are caused by the loss of acetic acid in the thin layer as the potential is increased from the reference to the adsorption value.…”

“…In the presence of 0.1 M HClO 4 (pH ∼ 1), non-dissociated form of acetic acid prevails in the solution. However, in a FTIR spectroscopy study, it has been proposed [7] that acetic acid molecules are adsorbed most likely on the top of the water molecules at polycrystalline metals. This model can be ascribed to adsorption of water molecules on the surface forming adsorbed hydroxyl ions.…”

Direct Ethanol Fuel Cell on Carbon Supported Pt Based Nanocatalysts

“…The formation of acetic acid can be seen by the appearance of two band at 1280 cm À1 and 1380 cm À1 [156][157][158] arising from the C-O stretch and -OH deformation, respectively. The presence of this molecule is also evidenced by the broad band at 2615-2650 cm À1 that is assigned to the asymmetric stretching ν(C-H) of the -CH 3 group [24].…”