Adsorption and oxidation pathways of thiourea at polycrystalline platinum electrodes

Garcı́a, Gonzalo; Rodrı́guez, José Luis; Lacconi, Gabriela I.; Pastor, E.

doi:10.1016/j.jelechem.2005.12.012

Cited by 23 publications

(32 citation statements)

References 35 publications

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“…, the electrode radius, r, and the bulk concentration, c. The process (a 1 ) is consistent with a one electron oxidation and the second anodic wave (a 2 ) has been attributed to the further multi-electron oxidation of formamidine disulfide cations to mixture of elemental sulfur, sulfate ions, carbon dioxide, and CN À containing product [24,25].…”

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confidence: 57%

“…Initially only the peak current for process a 2 , but then also the current for a 1 , is increased. This increase in current with scan rate may be attributed to adsorption of thiourea on platinum [24] causing additional oxidation currents. The second oxidation process, a 2 , appears to be mainly associated with adsorbed thiourea but it will be shown below that also process a 1 is substantially increased due to adsorption (when the surface area is increased).…”

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confidence: 99%

“…The voltammograms show that even at room temperature the electrooxidation currents for thiourea at a mesoporous Pt microelectrode has been enhanced by a factor of 6 for both anodic waves (a 1 ) and (a 2 ) in potential regions of 0.50 and 1.15 V vs. SCE. These results can be attributed to adsorption effects due to the ability of thiourea to bind to metal surfaces [24]. Due to the adsorption of thiourea onto the porous platinum the amount of reactant is considerably increased and therefore a higher (nonsteady state) current contribution is observed.…”

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Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum

et al. 2006

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In situ microwave activation is applied to the electrochemical oxidation of thiourea at low surface area (polished polycrystalline) and at high surface area (electrodeposited mesoporous platinum coated) platinum microelectrodes. The one electron oxidation of thiourea to formamidine disulfide is monitored as a function of the different activation parameters. In the absence of microwaves (ambient temperature, low mass transport) increasing the surface area (roughness) increases the thiourea oxidation response predominantly due to adsorption effects. In the presence of high microwave intensities, high mass transport and thermal effects further increase the oxidation current at mesoporous platinum. The most effective thickness of the mesoporous platinum film for the thiourea oxidation process is estimated as 3 mm independent of electrode diameter, temperature, or mass transport effects.

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Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum

et al. 2006

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“…[(H 2 N) 2 CS -] + + H 2 O → [(H 2 N) 2 CSOH 2 ] 2 + + ethat further decomposes, yielding a variety of products (including oxidation products) by a series of chemical and additional electrochemical steps depending on the experimental conditions (e.g., solution pH, applied potential and electrode material) Purdy 1981 , Yan et al 1996;Garcia et al 2006, Feng et al 2008. According to the previous suggestions, a possible explanation could be provided by the fact that at higher potentials TU-corresponding radical ion is consumed both by dimerization and by reacting with water.…”

Section: Electrochemical Behavior Of Tu On the Pg Electrodementioning

confidence: 99%

Electrooxidation of thiourea and its square-wave voltammetric determination using pencil graphite electrode

Levent¹,

Keskin

Yardım

et al. 2011

Reviews in Analytical Chemistry

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The electrochemical properties of thiourea (TU) were investigated in pH range 2.0 -12.0 by cyclic and square-wave voltammetry. The compound was irreversibly oxidized at a pencil graphite electrode in one or two oxidation steps which are pH-dependent. Based on the voltammetric peak for the second oxidation process of TU in phosphate buffer at pH 12.0, a square-wave voltammetric method was proposed for the determination of the compound in the range 6.3 -30 µ m , with a detection limit of 1.29 µ m . The applicability to direct assays of wastewaters was also tested.

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“…The presence of adsorbed TU and FDS species at metal electrodes and their role in the processes described above is a point still open to discussion. As expected from the strong sulfur-metal interaction, a variety of surface techniques has allowed the detection of irreversible adsorbed TU on gold and platinum electrodes in contact with TUcontaining solutions [4,6,[12][13][14][15][16]. Surface-Enhanced Raman Scattering (SERS) spectroscopy experiments proved the bonding of TU to the metal surface through the sulfur atom [12,13,[16][17][18].…”

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On the electrochemical behavior of formamidine disulfide on gold electrodes in acid media

Cheuquepán

Orts

Rodes

2016

Journal of Electroanalytical Chemistry

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Please cite this article as: William Cheuquepán, José Manuel Orts, Antonio Rodes, On the electrochemical behavior of formamidine disulfide on gold electrodes in acid media, Journal of Electroanalytical Chemistry (2016Chemistry ( ), doi: 10.1016Chemistry ( /j.jelechem.2016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT ABSTRACTThe adsorption and reactivity of formamidine disulfide (FDS) was studied at gold single crystal and thin film electrodes in perchloric acid solutions and the results of cyclic voltammetry and in situ infrared spectroscopy (SNIFTIR and ATR-SEIRAS) experiments compared with those previously obtained with thiourea (TU). In addition, optimized geometries and theoretical harmonic vibrational frequencies were obtained for adsorbed FDS, TU and thioureate from plane-wave DFT calculations using periodic surface models. These results were compared in the case of TU and thioureate to those previously obtained with a model Au cluster surface with (111) orientation. In the case of FDS, weak adsorption takes place with the S-S bond essentially parallel to the metal surface. No specific bands for adsorbed FDS can be identified in the experimental ATR-SEIRA spectra. These latter spectra suggest that adsorbed thioureate species are spontaneously formed upon dissociative adsorption of FDS when dosing this molecule at open circuit. Some of the adsorbed thioureate species undergo reductive protonation giving rise to a mixed adlayer formed by adsorbed thioureate and thiourea in a surface process which is faster when a controlled potential of 0.70 V is applied. In agreement with the observations reported when dosing TU, the ratio between TU and thioureate adsorbates is found to depend on the electrode potential, being higher for potentials close to the hydrogen evolution limit and decreasing for higher potential values. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 Graphical AbstractHighlights -FDS adsorbs weakly on Au with Au-S distances longer than those for TU and thioureate.-Physisorbed FDS dissociates homolitically to yield adsorbed thioureate.-Some adsorbed thioureate species are reduced to adsorbed thiourea.-Dosing conditions influence the rate of formation of adsorbed thiourea.-The thiourea/thioureate adsorbate ratio depends on the applied potential.

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Adsorption and oxidation pathways of thiourea at polycrystalline platinum electrodes

Cited by 23 publications

References 35 publications

Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum

Microwave Activation of Processes in Mesopores: The Thiourea Electrooxidation at Mesoporous Platinum

Electrooxidation of thiourea and its square-wave voltammetric determination using pencil graphite electrode

On the electrochemical behavior of formamidine disulfide on gold electrodes in acid media

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