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The Influence of teh Experimental Setup Upon the Modelling of the Impedance Spectra in Molten Salts

Kisza A., Kaźmierczak J., Meisner B.

Polish Journal of Chemistry

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2004

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Vol. 78 / nr 9

1235-1244

EN

To settle the frequently raised problem of the influence of cell geometry on the value of the evaluated by the electrochemical impedance spectroscopy (EIS) double layer capacitance, in this paper two types of cells have been tested in two and three electrodes experiments in molten salts. In the first type cell, the working silver electrodes were immersed directly in the molten NaCl - KCl eutectic mixture at 700°C, while in the second type cell, the working silver electrodes were placed inside quartz tubes connected to the bulk melt by a small hole. The only effect of the quartz tube was the desired increase of the electrolyte resistance from 0.7_ to 5.5 _, which is important in lowering the ac measuring current of the Solartron 1260 Phase Gain Analyser. The evaluated values of the double layer capacitance were to experimental uncertainty the same in both cells. It can be thus concluded, that the frequently raised in aqueous electrolytes problem of the influence of the cell geometry upon the values of the evaluated double layer capacitance, in molten salts does not lead to any significant errors. This is presumable due to the fact that the conductivity of molten salts is usually two order higher than aqueous electrolytes, and the corresponding ohmic drops are much smaller.

2

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.

3

Influence of the Silver Electrode Surface Structure on Electrochemical Adsorption on Thiourea in Perchloric Acid Solution

Smoliński S.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 10

1493-1504

EN

Electrosorption of thiourea (TU) on single crystal electrodes: Ag(111), Ag(100) and Ag(110) was studied using electrochemical and radiochemical methods. A radiotracer method, with TU labeled with C-14 in 0.1 M HClO4, was used to determine the surface concentration of the adsorbate. From radiometric data it follows that adsorption of TU is reversible with respect to the bulk concentration and the potential in the range of ideal polarizability of electrodes. The maximum surface concentration of TU, determined radiometrically, follows the sequence: Ag(111) _ Ag(100) _ Ag(110), which is in agreement with the atom surface density of the silver planes. The simple Langmuir adsorption equation describes experimental data up to 80% of surface coverage. The Gibbs energy of adsorption is similar (25.5 _ 1 kJ/mol) for all planes studied.