Electrochemical steady-state voltammograms

A steady state is independent of the details of the experiment used in attaining it. Thus, under conditions where a steady state is attained, e.g., under convective conditions in an - electrochemical cell, the application of a constant current leads to a constant potential and similarly the application of a constant potential leads to the same constant current. Voltammetric steady states are most commonly reached using linear potential sweeps (or ramps) in a single or cyclic direction at a UME or RDE. A sigmoidally shaped current (l)-potential (E) voltammogram (i.e., a steady-state voltammogram) is recorded in the method known as steady-state voltammetry as shown in the Figure. Characteristics of the... 

In the following we consider a simple electron transfer mechanism in order to discuss quantitatively the variations in the potential location of the steady-state voltammogram of the system according to the kinetics of the heterogeneous electron transfer. In the derivation of the kinetics we consider that the solution contains only the reactant at concentration C before the electrochemical experiment. Let E°, k, and a be the standard reduction potential, the standard heterogeneous rate constant, and the transfer coefficient of the electron transfer in Eq. (176). 

For slow scan rates, i.e., a few volts per second or slower, the voltammetric response of a miniaturized electrode is a sigmoid-shaped steady-state voltammogram [8]. Peak-shaped responses are observed (Mily when the scan rate is sufficiently high so that the depletion layer thickness is smaller than the critical dimension of the electrode. For example, a 50-nm-radius nanoelectrode requires the sweep rate to be of the order of 10,000 Vs to show the classical peak-shaped responses typically observed for electrochemically reversible systems at macroelectrodes at mVs scan rates. The theory describing mass transport to micro- and... 

Fig. 2.17 How a steady-state voltammogram is shaped by electrochemical (heterogeneous) kinetics...

Amatore, C. Fosset, B. Bartelt, J. Deakin, M. R. Wightman, R. M. Electrochemical kinetics at microelectrodes PartV. Migrational effects on steady or quasi-steady-state voltammograms. 7 7ecfn9a/Jo/... 

LCEC is a special case of hydrodynamic chronoamperometry (measuring current as a function of time at a fixed electrode potential in a flowing or stirred solution). In order to fully understand the operation of electrochemical detectors, it is necessary to also appreciate hydrodynamic voltammetry. Hydrodynamic voltammetry, from which amperometry is derived, is a steady-state technique in which the electrode potential is scanned while the solution is stirred and the current is plotted as a function of the potential. Idealized hydrodynamic voltammograms (HDVs) for the case of electrolyte solution (mobile phase) alone and with an oxidizable species added are shown in Fig. 9. The HDV of a compound begins at a potential where the compound is not electroactive and therefore no faradaic current occurs, goes through a region... 

Polish the GCE using diamond spray (particle size 1 pm) before every electrochemical assay. After polishing, rinse the electrode thoroughly with Milli-Q water for 30 s, then sonicate for lmin in an ultrasound bath and again rinse with water. After this mechanical treatment, place the GCE in pH 4.5 0.1 M acetate buffer electrolyte and record various DP voltammograms until a steady-state baseline voltammogram is obtained. This procedure is fundamental in order to obtain reproducible experimental results. 

As is well known, the steady-state behavior of (spherical and disc) microelectrodes enables the generation of a unique current-potential relationship since the response is independent of the time or frequency variables [43]. This feature allows us to obtain identical I-E responses, independently of the electrochemical technique, when a voltammogram is generated by applying a linear sweep or a sequence of discrete potential steps, or a periodic potential. From the above, it can also be expected that the same behavior will be obtained under chronopotentiometric conditions when any current time function I(t) is applied, i.e., the steady-state I(t) —E curve (with E being the measured potential) will be identical to the voltammogram obtained under controlled potential-time conditions [44, 45]. 

The electrochemical characterization of multi-electron electrochemical reactions involves the determination of the formal potentials of the different steps, as these indicate the thermodynamic stability of the different oxidation states. For this purpose, subtractive multipulse techniques are very valuable since they combine the advantages of differential pulse techniques and scanning voltammetric ones [6, 19, 45-52]. All these techniques lead to peak-shaped voltammograms, even under steady-state conditions. 

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