Portugaliae
Electrochimica Acta

Electrode surfaces modified, by monolayers of heavy metals underpotential deposited: Pt/M electrodes, electrode ads surfaces modified by over layers of their own oxides grown in-situ, i.e. Ir-oxide electrodes, and electrode surfaces with preferred orientations, namely Pt single crystals were the modified electrode surfaces selected for this lecture. The potentialities and advantages of the elec trochemical methods, namely cyclic voltammetry and potential step pulses to produce modified electrode surfaces and simultaneously to monitor changes and to test the stabili ty and the activity of the modified and non-modified electrode surface will be emphasized and illustrated with experimental data.

Porous carbon electrodes were prepared using carbon powders of different types using various catalysts. Physical properties of the prepared electrodes were evaluated using scanning electron microscopy (SEM), surface area analyser etc. Performance characteristics of these electrodes were evaluated by galvanostatic polarisation at various temperatures in 6M potassium and sodium hydroxide solutions.

Non-linearity of calibration in the determination of anions by ion-chromatography with supressed conductivity detection is re-examined. With a carbonate eluent, the curvature is demonstrated for NGg, Br" and SO*" calibrations using plots of the logarithm of the normalized peak area against the logarithm of the anion concentration. These graphs were also evaluated theoretically assuming the peak shape is Gaussian. It is demonstrated that for sufficiently low concentrations linear calibrations are obtained and that deviations are to be found in the middle of the concentration range. Several procedures are discussed to avoid having large errors in analysing samples over a wide range of concentrations.

This article presents a simple and cheap pilot plant instalation ior the Physical Chemistry Laboratory measurements (Electrochemistry). Various experiments concerning the aluminum surface treatments could be done: cleaning, polishing, anodizing and colouring. Furthermore, controling the required results as a function of time, temperature, current density, etc. can be achived by the proposed pilot plant.

The application of unequal space grid discretization to the solution of the diffusion equations in cyclic voltammetry by the line method (semi-discretization) is subjected to a preliminary analysis. It is shown that a carefully chosen exponentially expanding space grid can improve the accuracy of digital simulations by this method, although a significant improvement is only obtained for moderate values of the expanding parameter (larger values for this parameter result in performance degradation).