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The Electrochemical and Radiometric Study of Thiourea Adsorption on Polycrystalline Copper Electrode in Neutral Solution

Łukomska A., Sobkowski J.

Polish Journal of Chemistry

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2007

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Vol. 81, nr 12

2171-2180

EN

Adsorption of thiourea (TU) on a polycrystalline copper electrode from 0.01 M NaClO4 solution has been studied by impedance spectroscopy and radiometric method. differential capacity of copper electrode in 0.01 M NaClO4 solution containing TU of concentrations from 10-6 to 5.10-4 M has been measured. The dependencies of the surface concentration of TU on the electrode potential and the bulk concentration were determined radiometrically. The adsorption of TU on the copper electrode was studied in the range of potentials where no faradaic currents occurred. In this range the process of adsorption is practically reversible with respect to the potential and the bulk concen tration of TU. The experimental data were described by the Langmuir and virial isotherms and the Gibbs energy of adsorption was calculated. In order to show the role of the metal the data of TU adsorption on different electrodes have been compared. The unusual behaviour of TU on Cu electrode in comparison with the urea was commented.

2

Efekty powierzchniowej struktury metali w procesach elektrochemicznych

Sobkowski J., Jurkiewicz-Herbich M.

Wiadomości Chemiczne

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2004

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[Z] 58, 5-6

449--476

EN

It is known that both the nature and structure of a metal have a great influence on electrochemical processes. Interpretation of a mechanism of electrochemical reactions that occur on polycrystalline electrodes is often complicated because of their heterogeneous structure consisting of randomly distributed monocrystals on the surface. To avoid this problem, electrodes with well defined surfaces are commonly used in electrochemical experiments. In this paper, effects of the surface structure of a metallic electrode on properties of the double layer of the metal/solution interface, electrosorption and also on the electrochemical reactions has been reviewed. The presented data refer mainly to the basic planes of monocrystalline electrodes of face-centered cubic system. In first three chapters problems of the double layer structure of monocrystalline electrodes, the correlation of the potential of zero charge and work function, and the competition of a substrate and water molecules in the electrosorption process in relation to the hydrophilicity of metals are discussed. In chapters 4 and 5 the influence of the surface structure on the adsorption of organic molecules, strongly and weakly interacting with the electrode surface, is reviewed. It was shown that the surface concentration of adsorbate depends not only on the number of adsorption sites (assumed as the surface atom density) but also on the geometry of adsorbed molecule as well as on the kind and size of the supporting electrolyte anions. The latter play a very important role when the interaction of an adsorbed molecule and a metal is weak. Chapter 6 concerns the role of the electrode surface structure in the hydrogen ion discharge and also underpotential deposition of ions. The relationship between electrocatalytic properties of an electrode and its surface structure is presented in chapter 7. The kinetics of oxidation of methanol and formic acid at different planes of the platinum electrode and various products of the reduction of carbon oxide on copper monocrystalline electrodes are given as examples.

3

The Comparison of Electrochemical and Radiochemical Methods in Adsorption Study of Thiourea on the Polycrystalline Silver Electrode in Neutral Solution

Łukomska A., Sobkowski J.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 9

1135-1147

EN

Radiometry and impedance spectroscopy have been compared in the study of thiourea (TU) adsorption on polycrystalline silver electrode. Differential capacity of silver electrode in 0.01MNaClO4 solution containing TU of concentrations from 10-6 to 5_10-4M has been measured. The isotherms of TU adsorption, _ vs c determined from the capacitance and radiometric measurements have been compared and the Gibbs energy of adsorption was calculated. The experimental data were described by the Langmuir isotherm. The radiometric method allowed us to determine the surface concentration of TU. It was found that TU adsorption takes place in the entire range of the applied potential. The process of adsorption is reversible with respect to the electrode potential and the bulk concentration of TU, though the desorption process is not completed and small amounts of TU remain on the surface of Ag electrode.

4

Application of radiometric methods to the study of electrosorption and electrode reaction on solid electrodes

Sobkowski J.

Nukleonika

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1998

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Vol. 43, nr 4

399-414

EN

Two different radiometric methods employed for studying adsorption on the solid electrodes are reviewed. Both methods are applicable for direct and quantitative determinations of the adsorbate accumulated on the electrode surface. The first method, called the thin electrode method, is especially suitable for studies of adsorption of some organic substances, labelled with the β-emitters, on metals with rough surfaces. The method can be used to study adsorption as a function of bulk concentration, potential, time, temperature etc. The second method, which is called the lowering electrode (the thin gap) method, is used for adsorption studies on the smooth polycrystalline as well as on the monocrystalline electrodes. The structural effects in adsorption processes can be investigated as well. A modification of this method by the use of a standard source is discussed. Both methods presented are illustrated with some examples.

PL

Omówiono dwie metody radiometrycznego badania adsorpcji elektrochemicznej na elektrodach stałych. Obie metody pozwalają na bezpośrednie oznaczenie ilości zaadsorbowanej substancji. Pierwsza z nich, zwana metodą cienkiej elektrody, jest odpowiednia do badań adsorpcji substancji organicznych, znakowanych radionuklidami emitującymi cząstki β-, na elektrodach szorstkich o rozwiniętej powierzchni. Metoda ta pozwala na oznaczanie ilości zaadsorbowanej substancji w zależności od jej stężenia w roztworze, potencjału elektrody, czasu, temperatury itp. Druga metoda - metoda opuszczanej elektrody (zwana także metodą małego odstępu) - pozwala badać adsorpcję na elektrodach gładkich zarówno poli- jak i monokrystalicznych. Można tu śledzić wpływ struktury powierzchni na przebieg izoterm adsorpcji. Przedyskutowano modyfikację metody opuszczanej elektrody za pomocą źródeł standardowych. Obie metody zostały zilustrowane odpowiednimi przykładami.