Zofia Borkowska

On the real surface area of smooth solid electrodes

The determination of real surface area of the electrodes is very important for calculation of various parameters characterizing electrochemical processes. It has been noticed that real surface area determined by the electrochemical methods depends on the method used and on the experimental conditions. In this work the real surface area of the gold polycrystalline electrode is presented, determined by various electrochemical methods in aqueous and nonaqueous solutions with varying concentration of nonadsorbing electrolyte. In conclusion it is confirmed that the so-called roughness factor depends on the method used. The values of roughness factor determined for polycrystalline gold electrode using methods based on Gouy-Chapman theory are dependent on diffuse layer thickness via electrolyte concentration or solvent dielectric constant. These results are discussed in comparison with the theoretical predictions.

A double layer study of the (210) and (111) faces of gold in aqueous NaBF4 SOLUTIONS

Abstract Au(111) and Au(21O) faces of gold in aqueous NaBF4 solutions have been investigated using cyclic voltammetry and admittance measurements. On Au(21O) no specific adsorption of B F 4 − has been found. The results were first analysed accepting the Gouy-Chapman-Stern model for the double layer; like Ag(11O) and Ag(100) the inner layer capacity versus charge density curve has a broad maximum. For Au(111) it was not possible to draw clear conclusions and the variation of the inner layer capacity versus charge density seems to correspond to the accepted model only for the more negative densities of charge investigated. Models for the inner layer were discussed for the (210) face.

Medium effect: Electroreduction of Eu(III) in water+ acetone and water+N,N-dimethylformamide mixtures

Abstract The electroreduction of Eu(III) in water + acetone and water + N,N-dimethylformamide mixtures has been studied. For both systems the equilibrium potentials of the Eu(III)/Eu(II) couple, cobalticinium ion/cobaltocene, Cic+/Coc, system and bisdiphenylchromium (I/O)/ (BPC) in the whole composition range (except for pure acetone) have been measured. The standard rate constants and transfer coefficients for Eu(III) reduction on mercury electrode have been determined from the polarographic measurements in the case of water + acetone mixtures and from impedance measurements in the case of water + DMF mixtures. The problem of the potential scales has been discussed. In water-rich systems the aqueous calomel electrode and in organic-rich systems the BPC (I/O) or the hypothetical chloride electrode derived from real solvation energies seem to be adequate as reference potentials. Both Eu(III) and Eu(II) are probably more strongly solvated by DMF than by water, but less strongly by acetone. The kinetic data have been discussed on base of the model presented previously [3]. It can qualitatively account for the experimental curve with a minimum (Fig. 2) in water + acetone system and for an increase of the rate constant with additions of DMF. Also a decrease of activation energy by DMF should be taken into account.

Electrochemical study of the polycrystalline gold electrode in dimethylsulphoxide

Abstract The polycrystalline gold electrode has been studied in dilute LiClO4 solutions in dimethylsulphoxide using cyclic voltammetry and admittance measurements. Specific ionic adsorption is negligible in solutions more dilute than 0.1 M. The double-layer capacity depends on the potential programme applied to the electrode. It seems possible that some preferred crystallographic orientation is formed at the electrode when it is cycled in a narrow potential range close to the pzc. The inner-layer capacity obtained using the Gouy-Chapman-Stern model is much lower than that of the mercury electrode in the same solution. The potential drop across the inner layer has been discussed using Trasattis approach.

Adsorption of acetone on the mercury electrode from H2O+(CH3)2CO+HCl solutions

Abstract The adsorption of acetone on a mercury electrode from (CH 3 ) 2 CO+H 2 O+HCl solutions has been studied using a thermodynamically rigorous procedure. The chemical potential of the supporting electrolyte has been kept constant by using the concentrations corresponding to the constant e.m.f. of the cell with electrodes reversible to each of the ions in the solutions. It is suggested that the molecule is to some extent oriented with the hydrocarbon part towards mercury. The composition of the surface layer has been calculated.

Conductivity of stoichiometric (CH3)4NOH clathrate hydrates

Abstract The electrical properties of the Au ( CH 3 ) 4 NOH · H 2 O Au (n = 5, 7.5, 10) system have been studied by impedance spectroscopy at temperatures down to 130 K. One of the studied electrolytes (CH3)4NOH · 5H2O (TMAOH5) melts congruently, whereas others, (CH3)4NOH · 7.5H2O (TMAOH7.5) and (CH3)4NOH · 10H2O (TMAOH10), melt incongruently. The response of the cell Au TMAOH · H 2 O Au is typical for a polycrystalline electrolyte between solid blocking electrodes and it is temperature dependent. Linear, Arrhenius-type temperature dependences of the values of the resistive elements obtained from the best fit equivalent circuits are observed with the slope change at temperatures corresponding to a phase transition of the electrolyte. The corresponding activation energies of the conductivity Ea are equal to 0.30 eV (α-TMAOH5), 0.61 eV (β-TMAOH5), 0.18 eV (TMAOH7.5) and 0.17 eV (TMAOH10). The two latter values are among the smallest observed for solid protonic conductors. At a given temperature, the conductivities of TMAOH hydrates changes in the order TMAOH10 > TMAOH7.5 ⪢ TMAOH5 whereas the order of Ea values is the opposite: TMAOH10 ≤ TMAOH7.5 ≤ TMAOH5. The reasons for the observed differences in electrical conductivity of studied hydrates are discussed in terms of their crystallographic structure.

Conductivity of tetramethylammonium fluoride tetrahydrate

Abstract The conductivity of tetramethylammonium fluoride tetrahydrate (TMAF4) has been studied by impedance spectroscopy in the temperature range 213–322 K. The response of the cell Au|TMAF4|Au is typical for a polycrystalline electrolyte between solid blocking electrodes and it is temperature dependent. A conductivity drop of about two orders of magnitude is observed at temperatures around the melting point of TMAF4. Linear Arrhenius-type conductivity dependence is observed for the temperature ranges corresponding to the high and low temperature phases of solid TMAF4. The corresponding activation energies of conductivity are equal to 1.93 eV and 0.48 eV. The conductivity of TMAF4 is substantially lower than that of tetramethylammonium hydroxide pentahydrate (TMAOH5). However, TMAF4 can also be used in electrochemical studies. The reasons for the difference in conductivity between TMAF4 and TMAOH5 are discussed in terms of their crystallographic structures.

The adsorption of β-cyclodextrin on a dropping mercury electrode from aqueous solutions

Abstract The adsorption of β-cyclodextrin (β-CD) on a dropping mercury electrode has been studied in Na 2 SO 4 and phosphate buffer solutions by drop time measurements. β-CD is a strong adsorbant, half coverage, θ 2 , being reached in the solution containing 5 × 10 −5 M . The adsorption behaviour is similar to that for other non-polar, organic compounds such as simple sugars. The adsorption follows a Langmuir isotherm with ΔḠ max 0 = −34.7 kJ mol −1 . The adsorption isotherm can be used for the estimation of β-CD in the solution.

The electrical double layer at the mercury/solution interface in organic solvents

Abstract Double-layer data for the electrode/solution interface in organic solvents at various temperatures such as the differential capacity, the zero charge potential, interfacial tension and the entropy of formation of the interface derived from these, are discussed in terms of the interfacial solvent structure. Simple correlations between the experimental data are used to discuss the electrode-solvent interactions and the potential drop at the interface.

The Cooper-Harrison catastrophe in the case of the multistate models for unassociated solvent structure at polarizable interfaces

The possibility of occurrence of the so-called Cooper—Harrison catastrophe has been discussed in the case of a multistate model for unassociated solvent structure at a polarizable interface by Fawcett and de Nobriga. The catastrophe is avoided when the effective coordination number, Cc, is greater than 14.5. The case when Cc < 14.5 has been discussed.