Platinum Electrode In Acid Medium Research Articles

Electropolymerization of pyrrole and characterization of the obtained polymer films

AbstractElectrochemical oxidative polymerization of pyrrole on platinum electrode in acid medium was carried out. Different reaction parameters were investigated such as current density, acid concentration, monomer concentration, and temperature with duration of time. The orders of the electropolymerization reaction were found to be 1.3, 1.26, and 1.2 with respect to current density, acid concentration, and monomer concentration, respectively. The apparent activation energy was found to be 38.3 kJ mol−1. The obtained polymer films were characterized by 1H‐NMR, elemental analysis, thermogravimetric analysis, and cyclic voltammetry. The mechanism of the electrochemical polymerization reaction was also discussed. The surface morphology of the obtained polymer film was characterized by X‐ray diffraction and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1783–1792, 2003

FTIR spectroelectrochemical investigation of the electrocatalytic oxidation of ascorbic acid at platinum electrodes in acid medium

The electrochemical oxidation of ascorbic acid (AA) at a platinum electrode has been studied in 0.1 M HClO 4. In situ infrared reflectance spectroscopy (SPAIRS and SNIFTIRS techniques) was used to investigate the reaction intermediates. The identification of the different electroreactive species and adsorbed intermediates allowed us to postulate a reaction mechanism for the transformation of AA into dehydroascorbic acid (DHA).

Activated pulsed amperometric detection of cysteine at platinum electrodes in acidic media

AbstractAnodic voltammetric detection of sulfhydryl compounds, represented here by cysteine, at Pt electrodes in acidic media occurs concomitantly with anodic generation of surface oxide. It is speculated that the adsorbed hydroxyl species (PtOH), proposed to be the intermediate product in formation of the inert oxide (PtO), is the source of O‐atoms transferred to the sulfonic acid produced by oxidation of the sulfhydryl moiety. However, as a consequence of this electrocatalytic response mechanism, application of the traditional three‐step waveform for pulsed amperometric detection (PAD) of sulfhydryl compounds is accompanied by a large background signal resulting from PtO formation. To diminish the background signal, the traditional three‐step PAD waveform has been modified by insertion of a brief (100 ms) anodization step prior to the detection step to activate the Ptsurface by the generation of PtOH with minimal conversion to PtO. The subsequent negative step from the activation potential (Eact) to the detection detection potential (Edet < Eact) permits the PtOH to be harvested within the detection mechanism without significant background signal.

Electrocatalytic oxidation of propargyl alcohol at platinum electrodes in acid medium: A kinetic study

This paper deals with the electrocatalytic oxidation of propargyl alcohol (PA) at a platinum electrode in aqueous acid medium. During prolonged electrolyzes, the transformation is found to be highly selective towards the production of propargyl aldehyde (PAL). The effects on the selectivity of kinetic parameters, as the initial concentration of propargyl alcohol and the current density, are evaluated and correlated to the rate constant.

Vibrational spectroscopy of the electrochemical interface by visible infrared sum frequency generation

Vibrational properties of species adsorbed on platinum electrodes in the electrochemical environment are investigated by visible-infrared sum-frequency generation (SFG). Absolute vibrational spectra of adsorbed species are obtained by combining the inherent interfacial selectivity of SFG between centrosymmetric media and the use of a free-electron laser as infrared source. SFG spectra of hydrogen on polycrystal and single crystal platinum electrodes in acid medium are measured both in the under- and in the overpotential region. The vibrational fingerprints of the underpotential deposited hydrogen are structure sensitive and are related to its bonding to interfacial water molecules. On Pt(111) electrode, we have detected adsorbed hydrogen at potential as high as 0.35 V, within the so-called unusual adsorption state. A new hydrogen adspecies shows up in the overpotential range. Its vibrational signature is not dependent on the electrode surface orientation and we have assigned it to the intermediate of hydrogen evolution.

Vibrational spectroscopy of the electrochemical interface by visible-infrared sum-frequency generation

Vibrational properties of species adsorbed at the electrochemical interface are investigated by visible-infrared sumfrequency generation (SFG). Absolute vibrational spectra are obtained even for systems like H Pt with a very weak IR cross-section by combining the inherent interfacial selectivity of SFG between centrosymmetric media and the use of a free electron laser (FEL) as IR source. The potential dependence of SFG spectra of CN − on silver electrode in contact with (0.1M NaClO 4 + 0.01M KCN) solution gives access to the determination of the potential of zero charge and the adsorption behaviour of CN − on Ag. The SFG resonance spectra of intermediate species produced by the dissociative adsorption of methanol in Pt HClO 4 interface were recorded as a function of the electrode potential and the methanol concentration. Two resonances associated with the linearly and multi-bound CO have been identified. In contrast to previous IR studies, our results reveal a comparable occupation of both adsorption sites at high methanol concentration. Moreover the relative occupation of both sites strongly depends on methanol concentration, indicative of a dynamic equilibrium between species in solution and in adsorbed phase. Finally absolute vibrational spectra of hydrogen on a polycrystal and a single crystal platinum electrode in acid medium are measured both in the under and in the overpotential region. The vibrational fingerprints of the underpotential deposited hydrogen is structure sensitive and is related to its bonding to interfacial water molecules. A new hydrogen adspecies assumed to be the intermediate for the hydrogen evolution reaction shows up in the overpotential range. Its vibrational signature is not sensitive to the electrode structure.

A kinetic analysis of the electro-oxidation of ethanol at a platinum electrode in acid medium

In order to establish the kinetic laws which govern the oxidation process of ethanol on smooth platinum electrodes in acid medium, electrolyses of ethanol were carried out under different experimental conditions. The influence of the initial ethanol concentration and of the potential plateau of electrolysis were investigated and allowed us to improve our understanding of the reaction mechanism. In addition, some ir reflectance spectroscopy experiments were performed to identify the adsorbed intermediates and the reaction products.

Radiotracer study of anion adsorption in the course of oxidation of d-glucose at a platinized platinum electrode in acid medium

The adsorption of 36Cl labelled Cl − and 35S labelled HSO 4 −(SO 4 2−) ions at a platinized electrode was studied in the presence of glucose in strong acid medium. It was found that almost complete displacement of adsorbed HSO 4 − ions takes place at all potentials owing to the adsorption or adsorptive transformation of glucose. In contrast to this, the potential dependence of the adsorption of Cl − ions observed in the presence of glucose allows us to confirm the assumption made in the literature (I.T. Bae, X. Xing, C.C. Liu and E. Yeager, J. Electroanal. Chem., 284 (1990) 335; I.T. Bae, E. Yeager, X. Xing and C.C. Liu, J. Electroanal. Chem., 309 (1991) 131) that, depending on the potential, at least two types of adsorption of glucose should be taken into consideration.

The behaviour of germanium adatoms irreversibly adsorbed on platinum single crystals

Irreversible adsorption of foreign adatoms on the surface of a metallic substrate provides the possibility of handling stable modified electrodes for electrocatalytic purposes. In some cases, the irreversibly adsorbed adatom undergoes well-defined surface redox processes that have been shown to be structure sensitive. This is the case for As, Sb[l] and Bi[2] adatoms on platinum substrates with basal orientations. By means of the electric charges involved in the adatom redox process and those corresponding to the so-called hydrogen adsorption on the free platinum sites, it is possible to control the surface coverage of the adatom and the cleanliness of the electrode surface during handling. Lead [3] and tin [4,5] adatoms also adsorb irreversibly on platinum single crystal electrodes although the stability of oxidized lead species is achieved only in basic media [6]. In this work we report preliminary observations of irreversibly adsorbed germanium on well-defined platinum electrodes in acidic media. The behaviour of germanium adatoms on platinum has been studied carefully on polycrystalline platinum surfaces. As a result of the electrode pretreatment, which includes repetitive voltammetric cycles in a potential range including the adsorption-desorption of oxygen at full coverage [7], it is difficult to obtain structural information about the germanium adlayer. It has been pointed out, however, that there is a redox process involving the adsorption of oxygen on germanium adatoms at low potential values. The stability of this redox process under voltammetric conditions is similar to that observed with other irreversibly adsorbed adatoms. The germanium UPD process on single crystal platinum electrodes has also been studied in perchloric acid medium [8].

Radiotracer study of the adsorption of C-14 labelled d-glucose at a platinized platinum electrode in acid medium

The adsorption of C-14 labelled glucose was studied in 1 mol dm −3 H 2SO 4 supporting electrolyte over a wide potential range (from 0 to 1300 mV). In accordance with literature data, two characteristic sections in the apparent potential dependence of the steady state coverage with respect to adsorbed labelled molecules were found. The behaviour of adsorbed species formed predominantly in the potential range from 0 to 400 mV differs significantly from that of labelled molecules formed at higher potentials. It is shown that the experimental results cannot be treated in terms of “glucose adsorption” owing to the transformations of the original labelled molecules at the surface of the electrode.

Pulsed voltammetric detection of arsenic(III) at platinum electrodes in acidic media

The oxidation of As(OH) 3 at Pt is belleved to occur by an anodic oxygen-transfer mechanism that involves anodic discharge of H 2 O to form adsorbed hydroxyl radicals (PtOH); however, anodic conversion of PtOH to the inert oxide (PtO) results in severe passivation of the electrode surface. Hence, a transport-kimited response is not obtained at a Pt rotated-disk electrode by conventional linear scan or staircase voltammetry

Fourier-transform infrared studies of carbon monoxide adsorption on platinum and palladium hydrosols: influence of pH

Carbon monoxide adsorption on aqueous platinum and palladium sols has been studied by IR spectroscopy over the pH range 2.0–12.6. IR spectra of the CO-saturated platinum sols at pH ≈ 5.0 show a single asymmetric band at ca. 2070 cm–1 due to CO adsorbed linearly on platinum metal surface sites. The decrease in ν(CO)ads as pH is increased has been attributed to a decrease in coverage of adsorbed CO induced by hydroxyl adsorption. At pH 11.5. Correlations of ν(CO)ads with θ suggest that CO island formation is an important aspect of CO adsorption on both the platinum and palladium sols. It was found that CO adsorbed on colloidal platinum at pH < 4.0 does not exhibit similar behaviour to that of CO adsorbed on platinum electrodes in acidic media.

“In situ” infrared reflectance spectroscopic study of the early stages of ethanol adsorption at a platinum electrode in acid medium

The early stages of ethanol adsorption at a platinum electrode in acid medium are investigated using electrochemically modulated infrared reflectance spectroscopy (EMIRS). The superficial concentration of the different types of adsorbed species depends on the concentration of ethanol in the bulk, on the electrode potential and on the adsorption time. At low concentrations of C 2H 5OH, where the formation of CO ads appears to be slow, the observation of vibrational bands due to weakly adsorbed species becomes possible. Thus, enol-type species, like =CHOH, or adsorbed products, like CH 3COOH or CH 3CHO (bands at ≈ 1720 cm −1), are likely to be present at the electrode surface. Depending on the experimental conditions, other bands (sometimes complex) at 1200, 1305, 1380, 1620, 1825, 2350 and 3000 cm −1 are also detected. Their assignments are discussed.

Electrochemical studies of the adsorption of propargyl alcohol on a smooth platinum electrode in acid medium

The electrooxidation of the intermediate species produced by the adsorption of propargyl alcohol on a smooth platinum electrode has been studied in 0.5 M H2SO4 medium. At 25°C, the maximum amount of adsorbed intermediates was observed for Eads=0.2 V/rhe and the alcohol re-adsorption was avoided using a sweep rate ranging from 3 to 10 V s−1. The adsorption process is well described by a Temkin isotherm, with an interaction factor, f≈16, and an adsorption energy Δadso≈-49 kJ mol−1. The experimental data shown that the electrooxidation of propargyl alcohol proceeds through a reaction pathway involving an initial monoelectronic transfer step. In the temperature range from 20 to 80°C, the apparent activation energy for the electrooxidation of the adsorbed intermediates resulting from propargyl alcohol was determined, ΔHa*≈12 kJ mol−1.

Radiotracer study of the adsorption of Ca 2+ ions on a platinized platinum electrode in acid medium

The adsorption of labelled Ca 2+ ions was studied in the presence of various supporting electrolytes (HClO 4, HCl, H 2SO 4 and H 3PO 4 in 1 × 10 −2 mol dm −3 solutions) at low Ca 2+ concentrations ( c<10 −3 mol dm −3). It was found that the potential ( E) dependence of the adsorption (Γ) of Ca 2+ ions is influenced significantly by the nature of the anion. Problems connected with the shape of the Γ vs. E relationship are discussed. A link between hydrogen and Ca 2+ adsorption is assumed in the potential range from 0 to 250 mV (on RHE scale). The phenomena observed at more positive potentials are ascribed to the specific adsorption of anions.

Infrared spectroscopic study of methanol and formic acid adsorbates on a platinum electrode: Part I. Comparison of the infrared absorption intensities of linear CO(a) derived from CO, CH 3OH and HCOOH

The infrared absorption intensities of linear CO(a) derived from CO, CH 3OH and HCOOH, respectively, on a platinum electrode in 0.5 M H 2SO 4 were determined as a function of the total adsorbate coverage. The intensity of the CO(a) derived from HCOOH almost coincides with, although slightly lower than, that of the CO(a) derived from CO throughout the coverage range lower than ca. 0.9. The intensity of the CO(a) derived from CH 3OH almost coincides with that of CO(a) from CO only in the low coverage range. With increasing coverage from ca. 0.3, however, the intensity of the CO(a) from CH 3OH becomes progressively lower than that of the CO(a) from CO. It has been confirmed, based on quantitative comparison of the infrared absorption intensities, that the linear CO(a) derived from CH 3OH and HCOOH is in fact the predominant surface species on a smooth platinum electrode in acidic medium. However, the presence of minor surface species besides linear CO(a) has also been indicated from the intensity data.

Indirect radiotracer study of the adsorption of NO−3 ions at a platinized platinum electrode in acidic medium

Indirect radiotracer study of the adsorption of NO−3 ions at a platinized platinum electrode in acidic medium

Indirect radiotracer study of the adsorption of NO 3 ions at a platinized platinum electrode in acidic medium

Donnees sur une etude, par marquage isotopique indirect, de l'adsorption des ions NO 3 − en utilisant H 3 PO 4 marque P-32, comme espece indicatrice

Study of the electrocatalytic reduction of allyl chloride and chloral hydrate at a platinized platinum electrode in acidic medium

Electrocatalytic reduction and polarization behaviour of allyl chloride and chloral hydrate was studied at a platinized platinum electrode in acidic medium. In both cases formation of gaseous products has been observed. Allyl chloride transforms into propene and propane. The ratio of unsaturated and saturated hydrocarbons can be influenced by poisoning of the electrode with chemisorbed methanol. Polarization behaviour shows that the rate-determining step of the reaction is a charge-transfer process connected with the splitting of the C−Cl bond in allyl chloride. Reduction of chloral hydrate results in ethane (90%) and methane (10%). No simple polarization behaviour can be observed. A probable reaction sequence leading to the gaseous products is proposed on the basis of data obtained from electrocatalytic and catalytic studies.

Study of the electrocatalytic reduction of allyl chloride and chloral hydrate at a platinized platinum electrode in acidic medium

Electrocatalytic reduction and polarization behaviour of allyl chloride and chloral hydrate was studied at a platinized platinum electrode in acidic medium. In both cases formation of gaseous products has been observed. Allyl chloride transforms into propene and propane. The ratio of unsaturated and saturated hydrocarbons can be influenced by poisoning of the electrode with chemisorbed methanol. Polarization behaviour shows that the rate-determining step of the reaction is a charge-transfer process connected with the splitting of the C−Cl bond in allyl chloride. Reduction of chloral hydrate results in ethane (90%) and methane (10%). No simple polarization behaviour can be observed. A probable reaction sequence leading to the gaseous products is proposed on the basis of data obtained from electrocatalytic and catalytic studies.