Wyniki wyszukiwania - BazTech

1

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

|

2004

|

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 Double Layer Capacitance of the Liquid Lead Electrode in Molten NaX-KX (X=Cl, Br, I) Eutectic Mixtures

Kisza A., Kaźmierczak J., Meisner B.

Polish Journal of Chemistry

|

2004

|

Vol. 78 / nr 4

561-573

EN

Using the Electrochemical Impedance Spectroscopy, the double layer capacitance of the liquid lead electrode in the molten NaX-KX eutectic mixture has been evaluated at several temperatures at the rest potential, and in the potential range from 0 to -1Vagainst reversible lead electrode in the same melt. At no applied potential the liquid lead electrode in the studied eutectic melts can be treated as an "ideally polarizable" electrode. It has been found that the double layer capacitance at the rest potential is very small of the order of 0.9_F cm-2 for chloride, 0.6 for bromide and 0.2 _F cm-2 for iodide melts. As expected its value is decreasing with the increase of the temperature. At the far negative end of the potential range (-1.0 V), the double layer capacitance is decreased by the faradaic process (formation of the alkali metal - amalgam in liquid Pb).With the increase of the potential, the rate of this process decreases and the double layer capacitance increases.With a further increase of the potential, the alkali metal cations in the primary ionic shell are substituted by the halide anions, decreasing the charge density in the primary ionic shell, which results in the decrease of the capacitance toward some small value at the "potential of zero charge". Still further increase of the potential creates a new double layer, composed mainly of halide ions and the charge density increase is accompanied by the increase of the double layer capacitance. When the anodic dissolution of the metallic lead starts, another decrease of the double layer capacitance is observed. The evaluated values are much lower than the previous results, obtained in early sixties of the 20-th century, which has been obtained by the neglecting of the frequency dependence of the measured capacitance.

3

Mechanism and Kinetics of the Anodic Reaction in Cryolite Melts : I. The Influence of CaF2 (5 wt%) at Different Al2O3 Content

Kisza A., Thonstad J., Hives J.

Polish Journal of Chemistry

|

2000

|

Vol. 74, nr 4

549-558

EN

Calcium fluoride is one of the two main components of the cryolite-based electrolyte in aluminium electrolysis. By Electrochamical Impedance Spectroscopy (EIS) the influence of CaF2 upon the kinetics and mechanism of the anodic reaction in 4 cryolite-alumina melts containing 2,4,6 and 8 wt% of alumina. The diddusion coefficient of the Al2OF2- anionic species decreases as a function of the alumina content, due to the increase of the melts viscosity.

4

Mechanism and Kinetics of the Anodic Reaction in Cryolite Melts : II. The Influence of AIF3(11 wt%) at Different Al2O3 Content

Kisza A., Thonstad J., Hives J.

Polish Journal of Chemistry

|

2000

|

Vol. 74, nr 7

1003-1010

EN

Aluminium trifluoride is the main additive to the cryolite-based electrolyte in aluminium electrolysis. By Electrochemical Impedance Spectroscopy (EIS) the influence of AlF3 upon the kinetics and mechanism of the anodic reaction in 4 cryolite-alumina melts containing 2,4,6 and 8wt% of alumina and 11 wt% of AlF3 was determined at 1000 C.

5

Effect of the Preceding Chemical Reaction on the Hydrogen Electrode Reaction in Molten Ethylammonium Tetrafluoroborate

Więcek B., Kisza A.

Polish Journal of Chemistry

|

1999

|

Vol. 73, nr 8

1323-1331

EN

The hydrogen evolution reaction (HER) on platinum electrode in pure molten ethylammonium tetrafluoroborate (EABF4) has been investigated using a.c. impedance and potentiostatic steady-state polarization technique. The recorded impedance spectra have been discussed by an equivalent circuit approach and the theory of impedance of a quasi reversible electrode process preceded by a chemical (dissociation)reaction. The exchange current density of the HER, its activation energy, the diffusion coefficient of the hydrogen cation and the forward and backward rate constants of the preceding dissociation of ethylammonium cation have been determined.

6

Kinetics and mechanism of the silver electrode reaction in molten AgCl-NaCl binary mixtures

Kisza A., Dzielendziak J., Kaźmierczak J.

Polish Journal of Chemistry

|

1998

|

Vol. 72, nr 10

2321-2330

EN

Kinetics and mechanism of the silver electrode reaction in six melts of the binary AgCl-NaCl system were determined at several temperatures by Electrochemical Impedance Spectroscopy (EIS) and Relaxation Method with galvanostatic perturbation (RM). The exchange current density for this electrode process ranges from 2.5 to 4.5 cm(-2) for different melt composition. The diffusion coefficient of the silver ion and the activation parameters are also determined in melts containing 80 and 90 mol % of NaCl.