Polycrystalline Platinum Electrode Research Articles

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.

Electrochemical properties and electro-aggregation of silver carbonate sol on polycrystalline platinum electrode and its electrocatalytic activity towards glyphosate oxidation

This communication shows that colloidal suspensions of silver carbonate behave in a way which is new in voltammetric experience. Electrochemical signals typical of nucleation processes were observed during the electro-aggregation of silver carbonate on a platinum electrode. Modified electrodes, obtained by means of electro-aggregation of silver carbonate particles, showed catalytic activity towards the electrochemical oxidation of glyphosate, avoiding in this way typical passivation processes.

Electrocatalytic activity and simultaneous determination of catechol and hydroquinone at mesoporous platinum electrode

The electrochemical oxidation of catechol and hydroquinone was investigated using cyclic and differential pulse voltammetries at nanostructured mesoporous platinum film electrochemically deposited from the hexagonal liquid crystalline template of C 16EO 8 surfactant. The mesoporous platinum electrode has shown an excellent electrocatalytic activity and reversibility towards the oxidation of catechol and hydroquinone redox isomers in 1.0 M HClO 4. The oxidation and reduction peak separation (Δ E) has been decreased from 485 to 55 mV for hydroquinone and from 430 to 75 mV vs. SCE for catechol at polished polycrystalline and mesoporous platinum electrodes, respectively. The differential pulse voltammograms in a mixture solution of catechol and hydroquinone have shown that the oxidation peaks became well resolved and are separated by about 100 mV, although the bare electrode gave a single broad oxidation peak. Moreover, the oxidation current of hydroquinone and catechol has been enhanced by a factor of two and four times, respectively, at mesoporous platinum electrode. Using differential pulse voltammetry, a highly selective and simultaneous determination of hydroquinone and catechol has been explored at mesoporous platinum electrode.

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.

Surface-Immobilized Pyridine-Functionalized γ-Cyclodextrin: Alkanethiol Co-adsorption-Induced Reorientation

Monolayers of di-6A,6B-deoxy-6-(4-pyridylmethyl)amino-gamma-cyclodextrin (gamma-CD-(py)2) have been formed on polycrystalline platinum electrodes and investigated using electrochemical and surface-enhanced Raman spectroscopy (SERS). The behavior of self-assembled monolayers of (gamma-CD-(py)2) alone, (gamma-CD-(py)2) backfilled with 1-nonanethiol, and 1-nonanethiol are reported. The potential dependence of the capacitance indicates that the film capacitance is higher for the backfilled CD layers than for 1-nonanethiol layers, most likely due to ion flux through the CD cavity. SERS spectra of the backfilled layer exhibit features associated with both pyridine-functionalized CD and alkane moieties. Investigations using [Fe(CN)6]4- as a solution-phase probe indicate that the backfilled CD-alkane thiol layer exhibits enhanced blocking properties compared to gamma-CD-(py)2 films alone. Complete blocking was achieved by a combination of backfilling and insertion of a high-affinity guest 1-adamantylamine into the cavity. Significantly, an electroactive guest with high affinity for gamma-CD, [Co(biptpy)2]2+, does not exhibit a redox response at the gamma-CD-(py)2 layer but molecular recognition is turned on by backfilling the CD layer with 1-nonanethiol molecules. This switching on of the electrochemical activity suggests that the CD hosts are initially inaccessible but reorientate upon backfilling, exposing the CD opening to solution and permitting a supramolecular host-guest complex to form. The binding of [Co(biptpy)2]2+ to gamma-CD in the backfilled monolayer depends on the bulk concentration of guest and is modeled by the Langmuir isotherm, yielding an association constant for the Co2+ state of 1.45 +/- 0.46 x 105 M-1 and a limiting surface coverage 1.49 +/- 0.25 x 10-11 mol cm-2. The surface coverage of the divalent state is higher than the trivalent state, reflecting the dynamic nature of the inclusion.

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 ...

Effect of bismuth surface coverage on the kinetics of quinone–hydroquinone at polycrystalline platinum electrodes

Auger electron spectroscopy (AES), linear sweep voltammetry and coulometry have been used to investigate the effect of bismuth surface coverage over the electron-transfer kinetics of the quinone/hydroquinone (Q(aq)/H2Q(aq)) redox couple at Bi-coated polycrystalline platinum (Ptpoly) electrodes. In 0.5 M HClO4 acid solutions, the observed rate of electron-transfer is controlled by the relative bismuth surface coverage present at the Ptpoly electrode surface. At full bismuth monolayer coverages, the reversibility of the Q(aq)/H2Q(aq) redox couple is considerably enhanced. Continued potentiodynamic cycling of the Q(aq)/H2Q(aq) couple at a Bi-coated Ptpoly electrode leads to a decrease in the Q(aq)/H2Q(aq) redox rates. The decrease in redox rates is accompanied by the simultaneous decrease in Bi(ad) surface coverage and a concomitant increase in the chemisorption of hydroquinone-derived adspecies. Eventually, all Bi(ad) is displaced and electron-transfer takes place slowly, through a spontaneously adsorbed hydroquinone-derived adlayer. In sharp contrast, in the presence of 1 mM Bi(aq)3+, no changes are observed during potentiodynamic cycling of the Q(aq)/H2Q(aq) redox couple and the reaction rates remain fast.

Understanding CO-stripping mechanism from Ni UPD/Pt(1 1 0) in view of the measured nickel formal partial charge number upon underpotential deposition on platinum surfaces in sulphate media

We recently showed nickel-underpotential deposition (Ni-UPD) occurs on polycrystalline or single crystal platinum electrodes in acidic media. Whereas the decoupling of the nickel and hydrogen adsorption/desorption peaks is difficult for low pH, these processes can be better separated for higher pH values, typically pH > 3. However, even for platinum single crystals, high pH solutions do not enable to sufficiently separate nickel from hydrogen phenomena. As a result, electrochemistry alone cannot yield important information about Ni-UPD, such as the formal partial charge number (valency of electrosorption) and the role of the sulphate or hydrogen sulphate anions. So, we decided to couple cyclic voltammetry to electrochemical quartz crystal microbalance (EQCM). EQCM measurements enable to decorrelate the simultaneous hydrogen and nickel adsorption/desorption peaks, which we could not attempt solely with electrochemistry. The coupling between gravimetric and electrochemical measurements allows us to detect the contribution of the anions and thus to isolate that of nickel: nickel coverage can then be determined. Nearly 4/5 Ni UPD monolayer ( θ Ni ≈ 0.8) over platinum is reached at nickel equilibrium potential for high pH solutions (5.5). The QCM and electrochemistry coupling further allows the determination of nickel formal partial charge number: ι Ni,EQCM = 1.3 ± 0.13. Direct electrochemistry measurements (Swathirajan and Bruckenstein method) yield: ι Ni,Pt(poly) = 1.5 ± 0.17. These two values are close, which validates the electrochemical method for the nickel/platinum system. In consequence, we used Swathirajan and Bruckenstein method for Pt(1 1 0)-(1 × 2) crystal and found: ι Ni,Pt(1 1 0) ≈ 1.4 ± 0.1. Whatever the system (Ni UPD/Pt(poly) or Ni UPD/Pt(1 1 0)-(1 × 2)) or the experimental technique, nickel formal partial charge number is lower than nickel cation charge: ι Ni < z Ni = 2. In consequence, upon underpotential deposition on platinum surfaces, nickel cations discharge and then undergo additional charge exchange processes, such as anion (or water) adsorption, resulting in apparent partial nickel cation discharge. Moreover, Ni UPD/Pt(1 1 0) surface displays high activity towards CO ad oxidation reaction. We explain such positive effect by the possible existence of a bifunctional mechanism in which oxygenated-species-covered Ni UPD adatoms provide the oxygen atom to CO ad⋯Pt species, enabling its facile oxidation.

Enhancement of Toluene Formation by Water during Electrolysis of Chlorobenzene at Pt Electrode in Acetonitrile

Chlorobenzene was electrolyzed on polycrystalline platinum electrode in acetonitrile with various water concentrations at −3.02 V(vs. Fc/Fc+). Formation rate of the reduction products depend on water concentration remarkably. Benzene is a main product at [H2O]≤0.3 mol dm−3. At [H2O]≥0.35 mol dm−3, toluene is obtained as well as benzene. Partial current density of toluene gives maximum at [H2O]=0.44 mol dm−3. Formation of toluene closely relates with production of methane resulting from the decomposition of acetonitrile.

Electrochemical Behavior of the Li+/Li Couple and Stability of Lithium Deposits in Tri‐1‐Butylmethylammonium Bis((Trifluoromethyl)Sulfonyl)Imide Room Temperature Ionic Liquid

AbstractThe electrochemical behavior of the Li+/Li couple was studied at polycrystalline tungsten, platinum, copper and aluminum electrodes in tri‐1‐butylmethylammonium bis((trifluoromethyl)sulfonyl)imide ionic liquid mixed with a little propylene carbonate at 30 °C. Lithium cations were introduced into the ionic liquid by dissolution of lithium bis((trifluoromethyl)sulfonyl)imide which is highly soluble in ionic liquid. Propylene carbonate was used to reduce the viscosity of this ionic liquid in order to enhance the mass transfer and to additionally improve the stability of lithium deposits. At the tungsten and copper electrodes, the cyclic voltammetric behavior of a Li+/Li couple is a quasi‐reversible reaction. At the platinum electrode, the behavior becomes very complicated because of the alloy formation. Coulombic efficiency was used to evaluate the stability of lithium deposits at each electrode. The aluminum electrode showed the best efficiency due to the formation of Li‐Al alloy. However, lowest efficiency was obtained at the platinum electrode because of the low redox reversibility of the lithium in the Li‐Pt alloy. The diffusion coefficient of lithium cation in this solution was 1.0 ± 0.1 × 10−;7 cm2 s−;1 as determined by chronopotentiometry. The best coulombic efficiency obtained at the Al electrode is 97% but dropped to about 90% after 12 hours. The self‐discharge current of the lithium deposits at the Al electrode was 0.4 μA/cm2 during the experimental period.

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.

A DEMS study of the electrocatalytic hydrogenation and oxidation of p-dihydroxybenzene at polycrystalline and monocrystalline platinum electrodes

The electrochemical hydrogenation and oxidation of p-dihydroxybenzene (hydroquinone) chemisorbed at polycrystalline Pt, well-ordered Pt(111) and disordered Pt(111) electrodes were studied by differential electrochemical mass spectrometry (DEMS). For comparative purposes, benzene was investigated at polycrystalline Pt. Anodic oxidation yielded only CO2 as the volatile (DEMS-detectable) product. However, at least three oxidation cycles were necessary for exhaustive oxidation; this indicates that: (i) non-volatile products were generated in the first cycle, (ii) these products either stayed adsorbed or, in part, were re-adsorbed during a cathodic scan into the double-layer potential region, and (iii) these species were further oxidized on subsequent anodic scans. Electrocatalytic hydrogenation of hydroquinone at polycrystalline Pt followed two parallel (not sequential) paths to generate benzene and cyclohexane: the “branching ratio” was heavily in favor of the latter product. The adsorbate can be displaced by CO at potentials in the double layer region. Since no volatile species was observed during this process, the adsorbate is not already reduced; e.g., to benzene. On well-ordered Pt(111), no cyclohexane was produced and only a minuscule fraction of benzene was observed; however, quantitative desorption of (unidentified) non-volatile organic material took place at the negative potential. The disordered Pt(111) surface behaved more like the polycrystalline rather than the monocrystalline surface. The H2Q-hydrogenation reaction proceeds more readily on Pt with surface steps and kinks.

Electrochemical and Surface Characterization of 4-Aminothiophenol Adsorption at Polycrystalline Platinum Electrodes

The formation of a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been characterized by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), linear sweep voltammetry, Raman spectroscopy, reflection-absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). CV was used to study the dependence of the adsorption time and 4-ATP solution concentration on the relative degree of coverage of 4-ATP monolayers on polycrystalline Pt electrodes. The adsorption time range probed was 24-72 h. The optimal concentration of 4-ATP needed to obtain the highest surface at the lowest adsorption time was 10 mM. RAIR and Raman spectroscopy for 4-ATP-modified platinum electrodes showed the characteristic adsorption bands for 4-ATP, such as nuNH, nuCH(arom), and nuCS(arom), indicating the adsorption on the platinum surface. The XPS spectra for the modified Pt surface presented the binding energy peaks of sulfur and nitrogen. High energy resolution XPS studies, RAIR, and Raman spectrum for platinum electrodes modified with 4-ATP indicate that the molecules are sulfur-bonded to the platinum surface. The formation of a S-Pt bond suggests that ATP adsorption leads to an amino-terminated electrode surface. The thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses, giving a value of 8 A. As evidence of the terminal amino group on the electrode surface, the chemical derivatization of the 4-ATP SAM was done with 16-Br hexadecanoic acid. This surface reaction was followed by RAIR spectroscopy.

Bimetallic PtPb for formic acid electro-oxidation

Bimetallic PtPb had been synthesized by arc-melted and then sintering treatment. The electro-oxidation of formic acid on PtPb was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results are compared to those at a polycrystalline platinum electrode surface. It was found that PtPb Bimetallic was catalytically more active than pure platinum. Firstly, at the PtPb surface the peak potential for formic acid oxidation is shifted negatively by over 300 mV. Secondly, the current density at the PtPb electrode is dramatically higher than that for the Pt electrode. Thirdly, the ratio of the forward anodic peak current density ( I f) to the reverse anodic peak current density ( I b) for PtPb was much higher than that for the Pt electrode which indicated more intermediate carbonaceous species were oxidized to carbon dioxide in the forward scan on PtPb electrode surface. XRD and XPS technologies had been used to investigate the crystal structure and electron effect. It is proposed that formic acid decomposition on PtPb favors the reactive intermediate route and is not very much affected by the CO intermediate as compared to Pt.

Electrodeposition of Layered Manganese Oxide Nanocomposites Intercalated with Strong and Weak Polyelectrolytes

Multilayered manganese oxide nanocomposites intercalated with strong (poly(diallyldimethylammonium) chloride, PDDA) and weak (poly(allylamine hydrochloride), PAH) polyelectrolytes can be produced on polycrystalline platinum electrode in a thin film form by a simple, one-step electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn2+ ions at around +1.0 V (vs Ag/AgCl) in the presence of polyelectrolytes. Fully charged PDDA polycations are accommodated tightly in the interlayer space by electrostatic interaction with negative charges on the manganese oxide layers, leading to an interlayer distance of 0.97 nm. The layered film prepared with PAH has a larger polymer content (PAH/Mn molar ratio of 0.98) than that (PDDA/Mn molar ratio of 0.43) made with PDDA because of the smaller charging degree of PAH, exhibiting a larger interlayer distance (1.19 nm). The interlayer PAH contains neutral (-NH2) and positively charged (-NH3(+)) amine groups, and the -NH3(+) groups are associated with Cl- (to generate -NH3(+) Cl- ion pairs) as well as the negatively charged manganese oxide layers. Both polyelectrolytes once incorporated were not ion exchanged with small cations in solution. The layered structure of PDDA/MnO(x) was collapsed during the reduction process in a KCl electrolyte solution, accompanying an expansion of the interlayer as a result of incorporation of K+ ions for charge neutrality. On the contrary, the layered PAH/MnO(x) film showed a good electrochemical response due to the redox reaction of Mn3+/Mn4+ couple with no change in the structure. X-ray photoelectron spectroscopy revealed that, in this case, excess negative charges generated on the manganese oxide layers upon reduction can be balanced by the protons being released from the -NH3(+) Cl- sites in the interlayer PAH; the Cl- anions becoming unnecessary are inevitably excluded from the interlayer, and vice versa upon oxidation.

Bistability, oscillations and bifurcations of the electrocatalytic oxidation of HCHO on Pt

The electrocatalytic oxidation of formaldehyde on a polycrystalline platinum electrode is studied under potentiodynamic and galvanostatic conditions. It is shown that an extended dual path mechanism can reproduce the bistability, oscillations and bifurcation sequences observed experimentally.

Adsorption and oxidation pathways of thiourea at polycrystalline platinum electrodes

Abstract The present paper is related to study the adsorption and oxidation of thiourea (TU) on platinum electrodes in 0.1 M perchloric acid. A systematic electrochemical investigation was performed combining cyclic voltammetry with in situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) techniques to establish the nature of the species formed during these processes. It was concluded that TU adsorbs parallel on the platinum surface in the 0.20–0.55 V RHE potential range without faradic reaction. A dual-path reaction mechanism was evidenced in the oxidation process when TU was present in solution. The first reaction takes place from dissolved TU at E > 0.55 V RHE to form formamidine disulphide ( TU ) 2 2 + which is oxidized to soluble NH 2 CN at E > 1.30 V RHE . The second parallel reaction occurs from adsorbed TU at E > 0.60 V RHE and implies the formation of adsorbed species (NH 2 CN, SCN and S). In a following oxidation step at E > 1.10 V RHE , N 2 , CO 2 , and HSO 4 - / SO 4 2 - were produced. All these species were characterized from the spectroscopic experiments.

Determination of acrylamide and acrylic acid by isocratic liquid chromatography with pulsed electrochemical detection

The electrochemical behaviour of the polycrystalline platinum electrode towards the oxidation/reduction of short-chain unsaturated aliphatic molecules such as acrylamide and acrylic acid was investigated in acidic solutions. Analytes were separated by reverse phase liquid chromatographic and quantified using a pulsed amperometric detection. A new two-step waveform, is introduced for detection of acrylamide and acrylic acid. Detection limits (LOD) of 20 nM (1.4 μg/kg) and 45 nM (3.2 μg/kg) were determined in water solutions containing acrylamide and acrylic acid, respectively. Compared to the classical three-step waveform, the proposed two-step waveform shows favourable analytical performance in terms of LOD, linear range, precision and improved long-term reproducibility. The proposed analytical method combined with clean-up procedure accomplished by Carrez clearing reagent and subsequent extraction with a strong cation exchanger cartridges (SPE), was successfully used for the quantification of low concentrations of acrylamide in foodstuffs such as coffee and potato fries.

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.