Smooth Polycrystalline Platinum Electrodes Research Articles

A Study of Methanol Oxidation by Dynamic Electrochemical Impedance Spectroscopy

Methanol oxidation on a smooth polycrystalline platinum electrode is studied by dynamic electrochemical impedance spectroscopy at elevated temperatures employing an autoclave setup. By utilizing custom written software, impedance spectra for all applied electrode potentials are calculated. By increasing the temperature and/or sweep rate, it is shown that the region with three adsorbed species disappears, which is interpreted as less contribution of the parallel pathway at higher temperatures.

Electrocatalytic mechanism and kinetics of SOMs oxidation on ordered PtPb and PtBi intermetallic compounds: DEMS and FTIRS study

The electrocatalytic activities and mechanisms of PtPb and PtBi ordered intermetallic phases towards formic acid, formaldehyde and methanol oxidation have been studied by DEMS and FTIRS, and the results compared to those for a pure polycrystalline platinum electrode. While PtPb exhibits an enhanced electrocatalytic activity for the oxidation of all three organic molecules when compared to a Pt electrode, PtBi exhibits an enhanced catalytic activity towards formic acid and formaldehyde oxidation, but not methanol. FTIRS data indicate that adsorbed CO does not form on PtPb or PtBi intermetallic compounds during the oxidation of formic acid, formaldehyde and methanol, and therefore their oxidation on both PtPb and PtBi intermetallic compounds proceeds via a non-CO(ads) pathway. Quantitative DEMS measurements indicate that only CO(2) was detected as a final product during formic acid oxidation on Pt, PtPb and PtBi electrodes. At a smooth polycrystalline platinum electrode, the oxidation of formaldehyde and methanol produces mainly intermediates (formaldehyde and formic acid), while CO(2) is a minor product. In contrast, CO(2) is the major product for formaldehyde and methanol oxidation at a PtPb electrode. The high current efficiency of CO(2) formation for methanol and formaldehyde oxidation at a PtPb electrode can be ascribed to the complete dehydrogenation of formaldehyde and formic acid due to electronic effects. The low onset potential, high current density and high CO(2) yield make PtPb one of the most promising electrocatalysts for fuel cell applications using small organic molecules as fuels.

Electrodeposition of platinum metal on titanium and anodised titanium from P salt: application to electro-oxidation of glycerol

Pt/Ti and Pt/TiO2 electrodes were made by galvanic deposition of platinum metal from an acid plating bath containing cis-dinitro-diammin-platinum(II) complex (P salt) onto titanium and anodic TiO2 layer on titanium substrates respectively. Titanium oxide nanotubes were fabricated by anodising titanium foil in acid solution. Pt/Ti and Pt/TiO2 electrodes were characterised using electrochemical methods and scanning electron microscopy. Cyclic voltammetric analysis of Pt/Ti electrodes in dilute sulphuric acid yields voltammograms with features characteristic of bulk polycrystalline platinum electrodes. In contrast, the voltammograms for Pt/TiO2 electrodes are not quantitatively similar to those for smooth polycrystalline platinum electrodes. Voltammetry in potassium ferricyanide yields reversible voltammograms, indicating the good electrical conductivity of and connectivity between the deposited platinum and substrates and hence the absence of any significant resistive surface oxide film. The electrocatalytic behaviour of this type of electrodes in the glycerol electro-oxidation was studied.

Effect of oxygen adsorption on the laser-induced thermal jump of potential on a smooth polycrystalline platinum electrode

It has been shown for the first time that the laser-induced thermal jump of potential on a platinum electrode is sensitive to the form of oxygen adsorption.

Effect of ionic composition of solutions on the methanol reaction with adsorbed oxygen on smooth polycrystalline platinum electrodes: Transients of the open-circuit potential

Transients of the open-circuit potential observed in the reaction of methanol with oxygen (Oads) preliminarily adsorbed on smooth polycrystalline platinum (pcPt) are measured in 0.05 M HClO4, 0.5 M HClO4, 0.05 M H2SO4, 0.05 M H2SO4 + 0.45 M Na2SO4, and 0.05 M H2SO4 + 0.45 M Cs2SO4. It is shown that the solution pH has a weak effect on the transient characteristics (when the reversible hydrogen electrode potential scale is used). This confirms the chemical nature of rate-controlling stages in the reaction mechanism. The changes in the reaction rate, observed upon going from one electrolyte to another, are preferentially associated with the involvement of solution ions in the formation of activated surface complexes that include CH3OH, Oads, and supporting-electrolyte components.

DEMS Study on Methanol Oxidation at Poly- and Monocrystalline Platinum Electrodes: The Effect of Anion, Temperature, Surface Structure, Ru Adatom, and Potential

Methanol oxidation on Ru-unmodified and modified polycrystalline platinum, Pt(111), and Pt(332) was studied by on-line differential electrochemical mass spectrometry (DEMS) in combination with the dual thin-layer flow-through cell. The effects of anion, temperature, surface structure of Pt electrodes, Ru adatom, and potential on methanol oxidation were discussed. Methanol oxidation on smooth polycrystalline platinum, Pt(111), and Pt(332) electrodes proceeds via the parallel pathway mechanism, and mainly forms the soluble intermediates, i.e., formaldehyde and formic acid. Anion, temperature, and surface structure of Pt electrodes markedly influence the apparent rate of methanol oxidation; however, they do not significantly alter the current efficiency of CO2, and therefore do not change the mechanism of methanol oxidation. On pure platinum electrodes current efficiency of CO2 for methanol oxidation increases from ca. 20% to 32% with the increase of potential from 0.6 to 0.8V, accompanied by the increasing ...

Kinetics and mechanism of interaction between methanol and adsorbed oxygen on a smooth polycrystalline platinum electrode: Transients of the open-circuit potential

The method of transients of the open-circuit potential, combined with cathodic potentiodynamic pulses, is used for studying the methanol interaction with preliminarily adsorbed oxygen (Oads) in 0.5 M H2SO4. It is established that, for the larger part of the time period required for a full reduction of a monolayer of Oads in solutions of methanol on polycrystalline platinum, the process occurs at large coverages of the surface by Oads (ϑO). In the region of medium coverages, transients of the open-circuit potential are accurately described by the equation that corresponds to the mechanism of “conjugated reactions.” The mechanism of the methanol interaction with Oads happens to be close to that for formic acid, which is explained by a dissociative character of these HCO compounds. Kinetic parameters characterizing the methanol reaction with Oads in the region of large and medium coverages are determined and analyzed.

Voltammetric Characterization of Micro‐ and Submicrometer‐Electrode Arrays of Conical Shape for Electroanalytical Use

AbstractDensely packed micro‐ and submicrometer electrode arrays of platinum and gold (the nominal number, N, of electrodes in each array varies between 225 and 3600) are fabricated by photolithographic technique and vapor deposition processes of metal films. The electrodes are conical‐shaped and only their apexes are exposed to the electrolytic solution. The electrode arrays are characterized electrochemically in Ru(NH3)6Cl3 aqueous solutions by using cyclic voltammetry at low scan rates, to establish the number of electrochemically active electrodes (Nac) in each array; the geometric characterization is performed by scanning electron microscopy. All the investigated arrays provide steady‐state voltammograms, indicating diffusionally independent behavior of each microelectrode. The number of microelectrodes that are active in the fabricated arrays depends on microelectrode density. In particular, for the arrays with N=3600 and N=225, the fraction of active sites is about 45% and 90%, respectively. The analytical performance of some of the Pt version of the arrays is tested in hydrogen peroxide solutions, allowing verifying that linear calibration plots over the concentration range (0.1–20 mM) are obtained. This dynamic range is larger than that typically recorded at smooth polycrystalline platinum electrodes (0.5–5 mM), and the better performance is attributed to both the higher aspect ratio of the cone geometry and the higher mass transport associated to each microelectrode of the array. Reproducibility (within 3.5%, r.s.d.) and long‐term stability (within 5%, r.s.d., after 8 h continuous use) of the electrode systems are satisfactory. A low detection limit, based on the signal to noise ratio equal to 3, of 0.05 mM is found, which is adequate for a rapid monitoring of H2O2 in real samples and industrial processes.

Specific Features of the Adsorption of Carbon Monoxide on a Smooth Polycrystalline Platinum Electrode Modified with Adsorbed Silver Atoms

The adsorption of carbon monoxide at the surface of smooth polycrystalline platinum (smPt) is studied in conditions of a preliminary accumulation of various quantities of silver (θAg) on the surface. A comparison with similar data obtained previously for Pt/Pt is conducted. It is discovered that on smPt, exactly as in the case of Pt/Pt, carbon monoxide undergoes adsorption at sites that are not occupied by adsorbed silver, without forcing the preliminarily adsorbed silver out. At small and intermediate Agad, as opposed to Pt/Pt, a mere two peaks are observed in a voltametric curve in the region of electrodesorption of the mixed layer on smPt. It is shown that, in the region of potentials of the first peak, there occurs practically no transition of silver into solution in the course of oxidation of the mixed layer. Specific features that characterize the behavior of the COads + Agad mixed layer are discussed under the assumption about an “islet” character of the adsorption of silver.

Formation of intermediates during methanol oxidation : A quantitative DEMS study

Current efficiencies for the formation of CO2 during methanol oxidation at smooth polycrystalline platinum electrodes were determined by differential electrochemical mass spectrometry in a thin layer flow through cell. In all cases, the current efficiencies are below 60%; in particular, values as low as 16% were found in 0.1 M methanol solution at 0.6 V, which shows that a large amount of soluble intermediates (formaldehyde and/or formic acid) are formed. The extent to which these soluble intermediates are further oxidized to CO2 depends on the diffusion conditions. For methanol oxidation a parallel oxidation path via COad is also active. The influence of the surface crystal structure and, in particular, of steps was also studied. Step decoration by foreign metals allowed examination of the effect of cocatalytic metals on well defined model surfaces.

Electrode-surface coordination chemistry: ligand (-SH/I) substitutions at polycrystalline platinum

Ligand substitution (adsorbate displacement) reactions between iodine and the -SH functional group in 2,5-dihydroxythiophenol (DHT), previously investigated on Au, have been studied at a smooth polycrystalline platinum electrode in 1 M H 2SO 4. Experiments involved pretreatment of the Pt surface with a full monolayer of DHT (or iodine) followed by exposure to a dilute aqueous solution of KI (or DHT) Thin-layer electrochemistry and X-ray photoelectron spectroscopy were then used to characterize the DHT and/or I that remained on the surface. The results were as follows: (i) exposure of the I-coated surface to DHT led to the displacement of 40% of the original I and the incorporation of 70% of a monolayer of DHT; exposure of the DHT-coated Pt to KI yielded a layer that retained at least 90% of the original DHT and the coadsorption of no more than 10% of a monolayer of iodine. This observation indicates that, on Pt, the -SH functional group is selectively surface-coordinated over I; the converse occurs on Au where I is preferentially chemisorbed over DHT; (ii) The presence of coadsorbed I disrupts the substrate-mediated DHT-DHT interactions, as indicated by the sharpening of the reversible redox peaks of the pendant diphenolic moiety, on going from pure DHT to mixed I-DHT adlayers. On Au, the redox peaks were equally sharp whether or not iodine was present on the surface; (iii) The apparent molecular cross-section of DHT in the mixed I-DHT layer (0.20 nm 2) was less than that in the pure DHT layer (0.31 nm 2). This result, along with the coadsorbed-I-induced diminution of the redox peak widths, suggest that, as on Au, the coadsorbed I and DHT species are distributed homogeneously, not heterogeneously as distinct domains of pure I and pure DHT.

Electrochemical studies of the adsorption of aniline on a smooth polycrystalline platinum electrode

Adsorption of aniline on smooth polycrystalline platinum was studied in 0.5 M H 2SO 4 aqueous medium as a function of the aniline concentration (10 −8 – 10 −3 M) and electrode potential (−670 to + 1000 mV (MSE)) by potential programmed voltammetry. The adsorption kinetics and isotherms were investigated at constant potential. Possible orientation models were proposed for adsorbed compound.

Radiotracer study of adsorption of HSO −4 ions induced by Cd 2+ adatoms at a smooth polycrystalline platinum electrode

Sulfate adsorption induced by cadmium adatoms on a smooth polycrystalline platinum electrode has been studied in 0.1 mol dm −3 HClO 4 supporting electrolyte. Earlier work carried out with platinized electrodes has been confirmed, which prompts the initiation of more detailed studies at well-defined smooth electrode surfaces.

Chemisorption and electrocatalytic reactivity of 3,6-dihydroxypyridazine at Au and Pt electrodes: a comparison

The chemisorption and electrocatalytic reactivity of 3,6-dihydroxypyridazine (DHPz) has been compared at smooth polycrystalline platinum and gold electrodes in aqueous acid and neutral solutions. Analytical measurements of packing densities and electrochemical reactivities were based upon thin-layer electrochemical techniques. At ambient temperatures, DHPz irreversibly adsorbs on Pt via only one nitrogen, regardless of pH. This means that the driving force for coordination of the nitrogen heteroatom to the Pt surface is greater than its protonation, even in molar acid. The same mode of η 1-N attachment also occurs on gold but saturation or space-limited coverages are not attained in very acidic media. Evidently, the driving force for protonation of the nitrogen heteroatom in molar acid is about the same magnitude as its coordination to the Au surface. The surface-coordination strength of DHPz is therefore greater on Pt than on Au. Chemisorbed DHPz can be hydrogenated and oxidized at both electrodes, although the extent of these reactions is lower on Au than on Pt. Coulometric measurements suggest that oxidation of surface-coordination DHPz is limited to cleavage of the NN bond and formation of terminal nitro groups.

Electrocatalytic hydrogenation and oxidation of model coal-derived compounds chemisorbed at smooth polycrystalline Pt: a survey

The chemisorption and electrocatalytic reactivity of six model coal-derived compounds at smooth polycrystalline platinum electrodes in aqueous solutions have been investigated. The compounds studied were aniline (AN), hydroquinone (HQ), 3,6-dihydroxypyridazine (DHPz), 2,3-dihydroxypyridine (DHPy), 2,5-dihydroxythiophenol (DHT), and thiophene (TP). Electrocatalytic hydrogenation and oxidation using thin-layer electrochemical cells were carried out at −0.25 V [Ag/AgCl (1 M Cl −) reference] and 1.18 V, respectively, in 1 M H 2SO 4 in the absence of bulk (unadsorbed) species. Electrocatalytic hydrogenation was characterized by the average number of hydrogen atoms n H reacted per chemisorbed molecule, and anodic oxidation was investigated in terms of the effective number of electrons n ox transferred during the oxidation reaction. The results indicate that: (i) Hydrogenation of benzene to cyclohexane, which is a function of the initial adsorbate orientation, is a more facile process than hydrogenolysis of the aromatic ring. (ii) Hydrogenation of the aromatic ring proceeds more readily than cleavage of the C-O bond even if the oxygen heteroatom is not part of the aromatic ring. (iii) Hydrogenative cleavage of the C-S bond occurs more readily and with greater specificity if the sulfur heteroatom is not part of the aromatic framework. (iv) Hydrogenative cleavage of the C-N bond also takes place more easily and with higher specificity if the nitrogen heteroatom is not part of the aromatic ring. (v) Anodic oxidation is dependent upon orientation or mode of attachment, if the orientational states of a given molecule are vastly different from one another, as in η 6-HQ and 2,3-η 2-HQ; if the alternative orientations are similar, as in S-η 1 and tilted DHT, n ox may be independent of initial orientation. (vi) For a given mode of surface attachment, the extent of anodic oxidation is a function of the structure of the aromatic ring. (vii) In general, hydrogenation is limited to the functional group directly bonded to the Pt surface; no such limitation applies to catalytic oxidation.

The influence of orientation on the electrocatalytic hydrogenation of hydroquinone chemisorbed at smooth polycrystalline platinum electrodes

Abstract The influence of orientation on the electrocatalytic hydrogenation of hydroquinone (HQ) chemisorbed at smooth polycrystalline platinum electrodes in aqueous solutions has been investigated; experimental measurements, performed in the absence of bulk (unadsorbed) HQ, were based upon thin-layer electrochemical techniques. The extent of hydrogenation was characterized by (i) n H . the average number of hydrogen atoms reacted per chemisorbed HQ molecule, and (ii) the electrolytic charge Q ox for oxidation of chemisorbed organic which remained on the surface after the hydrogenation reaction. The measured values of n H indicate that the extent of HQ hydrogenation is (i) dependent upon the potential E Hyd at which hydrogenation was earned out, and (ii) a sensitive function of its initial adsorbed orientation; at a given E Hyd , n H is larger in the flat (η 6 ) than in the edge (2,3-η 2 ) orientation. Correlation of Q ox with n H , indicates that an appreciable fraction of partially hydrogenated species is desorbed from the surface; this fraction, which is a function of E Hyd , is larger in the 2.3-η 2 than in the η 6 orientation.

Surface coordination chemistry of noble-metal electrodes. Hydrogen/iodine ligand (adsorbate) substitution at smooth polycrystalline platinum

Adsorbate (ligand) displacement/substitution has been found to occur between iodine and hydrogen at smooth polycrystalline platinum electrodes in aqueous acid, neutral, or base electrolyte; experimental measurements were based upon thin-layer electrochemical methods. The iodine/hydrogen substitution reaction is a two-electron redox-activated process, the mechanism of which appears to depend upon the pH of the solution. In the absence of an applied potential, iodine is the only species present on the Pt surface. When a negative potential is applied in the vicinity of the hydrogen evolution reaction, chemisorbed iodine is progressively desorbed as iodine ions accompanied by the immediate chemisorption of protons as hydrogen atoms; when the potential is subsequently made positive, the reverse displacement reactions occurs in which hydrogen is oxidatively desorbed as protons accompanied by the oxidative chemisorption of iodine as iodine. In acid media, iodine desorption occurs after evolution of molecular hydrogen, in basic solutions, iodine removal occurs before electrogeneration of hydrogen gas.

Hydrogenative/cathodic stripping of iodine chemisorbed on smooth polycrystalline platinum electrodes

Hydrogenative/cathodic stripping of iodine chemisorbed on smooth polycrystalline platinum electrodes

Effect of non-aqueous solvents on the chemisorption and orientation of aromatic compounds at smooth polycrystalline platinum electrodes: naphthohydroquinone and tetrahydroxybiphenyl in water + acetonitrile solutions

The chemisorption of 1,4-naphthohydroquinone (NHQ) and 2,2′,5,5′,-tetrahydroxybiphenyl (THBP) at smooth polycrystalline Pt electrodes has been studied in aqueous solutions containing preselected amounts of acetonitrile (ACN), a widely-used non-aqueous solvent. Chemisorption measurements were made with thin-layer electrodes. The presence of ACN in solution led to a mixed organic layer whose composition showed a dependence on the ACN-to-aromatic concentration ratio. The comparatively weak adsorbability of ACN was manifested by the fact that, at an ACN-to-aromatic ratio of 100:1, the amount of THBP chemisorbed was still about 60% of the value measured in the absence of ACN. THBP chemisorption was still present at much higher ACN/THBP ratios, but the adsorption data for reversibly-electroactive THBP indicated that under these severe conditions THBP was chemisorbed only in the edgewise orientation. That is, the adsorbability of ACN was such that, when present at high bulk concentrations, ACN completely suppressed THBP chemisorption in the flat (but not in the edgewise) orientation. Extrapolation from these results of adsorption from weak ACN solutions suggests that adsorption of aromatic would be limited to small amounts of edgewise-oriented adsorbate.

Ordered disordered packing in mixed chemisorbed layers: vertically oriented polyphenolic compounds at smooth polycrystalline platinum electrodes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOrdered disordered packing in mixed chemisorbed layers: vertically oriented polyphenolic compounds at smooth polycrystalline platinum electrodesDian Song, Manuel P. Soriaga, and Arthur T. HubbardCite this: Langmuir 1986, 2, 1, 20–23Publication Date (Print):January 1, 1986Publication History Published online1 May 2002Published inissue 1 January 1986https://doi.org/10.1021/la00067a003RIGHTS & PERMISSIONSArticle Views41Altmetric-Citations5LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (480 KB) Get e-Alerts Get e-Alerts