Potential step methods reversal experiments

Such effects are observed inter alia when a metal is electrochemically deposited on a foreign substrate (e.g. Pb on graphite), a process which requires an additional nucleation overpotential. Thus, in cyclic voltammetry metal is deposited during the reverse scan on an identical metallic surface at thermodynamically favourable potentials, i.e. at positive values relative to the nucleation overpotential. This generates the typical trace-crossing in the current-voltage curve. Hence, Pletcher et al. also view the trace-crossing as proof of the start of the nucleation process of the polymer film, especially as it appears only in experiments with freshly polished electrodes. But this is about as far as we can go with cyclic voltammetry alone. It must be complemented by other techniques the potential step methods and optical spectroscopy have proved suitable. 

This experiment, called double potential step chronoamperometry, is our first example of a reversal technique. Such methods comprise a large class of approaches, all featuring an initial generation of an electrolytic product, then a reversal of electrolysis so that the first product is examined electrolytically in a direct fashion. Reversal methods make up a powerful arsenal for studies of complex electrode reactions, and we will have much to say about them. 

In connection with the above statements a next step has been made in the investigations, namely studying the influence of the Ce and Ce + ions as components of the corrosion medium (O.IN H2SO4) on the anodic behavior of stainless steel. These investigations were provoked by the observed occurrence of cathodic depolarization reaction of Ce + (CeCb) reduction, as a result of which the surface concentration of cerium is decreasing and theoretically it should approach zero value (Stoyanova et al., 2010). For this purpose an inverse experiment was carried out at different concentrations of Ce + ions in the corrosion medium we monitored the changes in the stationary corrosion potential of the thermally treated steel by the chronopotentiometric method. The aim of this experiment was to prove the occurrence of a reversible reaction of reduction of Ce + Ce +- e <-> Ce , (instead of the reaction of hydrogen depolarization), which in its turn creates also the option to form a film (chemically insoluble) of cerium hydroxides/oxides on the active sections of the steel surface. 

The selection of starting conditions is the first step in HPLC method development. Instead of starting with arbitrary conditions or conditions derived from the chromatographer s experience or intuition, the software can predict suitable initial conditions for reversed-phase methods from analyte structures and properties of the sorbent/solvent system [1-3]. If structures are known, the theoretical approach has the potential to save time and effort, since in this way the experimental method development process will start under the theoretically predicted optimum conditions. 

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