Joanna Taraszewska

Electrocatalytic oxidation of methanol on a glassy carbon electrode modified by nickel hydroxide formed by ex situ chemical precipitation

The properties of a glassy carbon (GC) electrode modified by nickel hydroxide formed by ex situ chemical precipitation were studied by cyclic voltammetry in alkaline solutions, and compared with the properties of the GC electrode modified by nickel tetraazamacrocyclic complexes. It was found that the GC/Ni(OH)2 modified electrode acts as an effective catalyst for the oxidation of methanol.

Electrocatalytic oxidation of alcohols on glassy carbon electrodes electrochemically modified with nickel tetraazamacrocyclic complexes: mechanism of f

Abstract The properties of glassy carbon (GC) electrodes modified with tetraazamacrocyclic complexes of Ni(II) containing a pendant amino group have been studie the properties of a Ni-cyclam modified electrode. It has been found that GC electrodes modified with all the complexes studied act as very effective ca modifying the film formation has been discussed.

Kinetics of Zn2+ reduction at a Hg electrode from water-acetone and water-methanol mixtures

Summary The kinetics of the reduction of Zn 2+ ions at a mercury electrode from water-acetone and water-methanol mixtures has been studied. The dependence of the kinetic parameters on the solvent composition and on the kind and concentration of the supporting electrolyte has been discussed. It was pointed out that in the case of mixed solvents, if the electrolyte is strongly preferentially solvated by water, e.g. NaF in H 2 O + acetone, it can produce pronounced effects due to changes in the activities of the solvent components. The effect of solvent composition on the kinetics of electrode reactions has been discussed in terms of the equilibrium concentration of depolarizer in the surface phase σ adjoining the electrode, where the solvent composition is different from that in the bulk α. The equilibrium is determined by the free enthalpy of transfer α Δ σ G t of Zn 2+ ions from phase α to σ. A correction factor for the concentrations of Zn 2+ at the surface expressed as exp (− α Δ σ G t / RT ) included into the kinetic equation can account for the minimum at the log κ F vs. χ CH 3 COCH 3 curve. Such a correction term is similar in its nature to the generally used Frumkin correction for the potential drop in the diffuse double layer.

Inclusion complexes of isomeric chloronitrobenzenes with α- and β-cyclodextrins studied by polarography: Analysis of the possibilities of the method

Abstract Inclusion complexes of isomeric chloronitrobenzenes with α- and β-cyclodextrins in 0.1 and 0.5 M phosphate buffer (pH = 7) have been studied by polarographic and voltammetric methods. The stability constants and the diffusion coefficients of the corresponding complexes have been determined. The possibilities of the polarographic method based on the determination of diffusion coefficients for the calculation of the stability constants of inclusion complexes have been discussed and checked using digital simulations.

Medium effect. Adsorption of dimethylsulfoxide on the mercury electrode from dimethylsulfoxide+water+NaClO4 mixtures

Abstract The adsorption of DMSO on the mercury electrode from DMSO + H 2 O + 0.9 M NaClO 4 mixtures has been determined in a thermodynamically rigorous way. For this purpose the change of the chemical potential of NaClO 4 with change of the chemical potential of DMSO has been estimated. The problem of potential scale is discussed. It is suggested that with increasing DMSO content in solution the DMSO molecules undergo some reorientation on the mercury surface.

Medium effect: Kinetics of Zn(II) and Cd(II) reduction at the Hg electrode from water + dimethylsulfoxide mixtures

Abstract The kinetics of Zn(II)/Zn(Hg) and Cd(II)/Cd(Hg) electroreduction have been studied in dimethylsulfoxide (DMSO) and water + DMSO mixtures. The diffusion coefficients, the relative Walden products and the charge-transfer rate constants have been determined and compared with those for Pb(II) and Mn(II) reported in the literature. The results obtained are discussed taking into account the structure of the double layer as well as the solvation energy of the cations in these mixtures. The change in the kinetics with solvent composition is discussed in terms of existing models. A new interpretation is proposed in which the concentration term and the change in activation energy of the electrode process are taken into account.

Application of glassy carbon electrode modified with Nitetraazamacrocyclic complexes in carbonate solutions to electrocatalytic oxidation of alcohols

Abstract The properties of a glassy carbon (gc) electrode modified with Ni-tetraazamacrocyclic complexes in carbonate media were studied by cyclic voltammetry. It was found that such an electrode acted as an effective catalyst for the oxidation of methanol and other simple alcohols.

Medium effects in the systems: Cd2+ or Zn2+ in some water+organic solvent mixtures deduced from equilibrium potentials at amalgam electrodes

Abstract The preferential solvation of Cd 2+ , Zn 2+ and Na + ions in H 2 O+CH 3 OH and H 2 O+DMSO mixtures was studied on base of equilibrium potential measurements. The electrolyte used was 0.1 and 0.9 M NaClO 4 . The Cic and BBCr reference systems were compared in H 2 O+DMSO mixtures. The BBCr system seemed to be more satisfactory. From the equilibrium potentials referred to BBCr the values of the transfer energies of Cd 2+ , Zn 2+ and Na + ions from H 2 O to DMSO or to CH 3 OH were estimated. The transfer energies of Zn 2+ and Cd 2+ ions as functions of x DMSO decreased monotonically indicating the selective solvation by DMSO in the whole composition range. The limiting values of Δ G tr for pure DMSO were −45 kJ mol −1 and −58 kJ mol −1 for Zn 2+ and Cd 2+ ions, respectively. The effects were small in the case of Na + ions and no unambiguous conclusions concerning its selective solvation in this system could be drawn. In H 2 O+CH 3 OH mixtures the effects of selective solvation were very small for all three cations up to X CH 3 OH =0.8.

In-situ surface-enhanced Raman spectroscopic study of gold electrodes modified with nickel tetraazamacrocyclic complexes

The redox behaviour of films deposited on roughened gold electrodes in strongly alkaline solutions containing Ni-tetraazamacrocyclic complexes was monitored by potential-dependent surface-enhanced Raman scattering spectra in conjunction with cyclic voltammetry. Spectra were recorded on modified electrodes and during the procedure of electrode modification. It has been found that the complexes studied do not decompose in the procedure of modification and that they are attached to the electrode surface and interconnected via the oxo-bridges.

Medium effect: kinetics of Zn2+ reduction at the Hg electrode from water + dimethylformamide mixtures

Abstract The kinetics of Zn2+/Zn(Hg) electroreduction have been studied indimethylformamide (DMF) and in H2O+DMF mixtures. The diffusion coefficients, formal potentials and the charge transfer rate constants have been determined. The transfer energies of Zn2+ from H2O to H2O+DMF mixtures have been estimated on the basis of equilibrium potential measurements referred to BCr, Cic and Fc redox couples. The differential double-layer capacity and potentials zero charge have been measured and the adsorption of DMF from H2O+DMF+0.9 M NAClO4 has been evaluated. The kinetic results are discussed taking into account the concentration correction term and the activation energy of the electrode reaction.