Chronoamperogram: potential step

These two equations quantify the evolution of the relaxation current and the relaxation charge as a function of the polarization time when the conducting polymer is submitted to a potential step from Ec to E. They are the relaxation chronoamperogram and the relaxation chronocoulogram,... 

For chronoamperograms obtained by potential steps from the same cathodic potential to different anodic potentials ... 

Figure 3.3 Chronoamperometry. (A) Potential excitation signal for double potential step. (B) Current-time response signal (chronoamperogram).

Current as a function of time is the system response as well as the monitored response in chronoamperometry. A typical double-potential-step chronoamperogram is shown by the solid line in Figure 3.3B. (The dashed line shows the background response to the excitation signal for a solution containing supporting electrolyte only. This current decays rapidly when the electrode has been charged to the applied potential.) The potential step initiates an instantaneous current as a result of the reduction of O to R. The current then drops as the electrolysis proceeds. 

Understanding the shape of the chronoamperogram requires consideration of concentration-distance profiles for a potential-step excitation in conjunction with Faraday s law. Faraday s law is so fundamental to dynamic electrochemical experiments that it cannot be emphasized too much. It is important to keep in mind that the charge Q passed across the interface is related to the amount of material that has been converted, and the current i is related to the instantaneous rate at which this conversion occurs. Current is physically defined as the rate of charge flow therefore,... 

As a further practical tip, for an OTE based on a thin conductive optically transparent layer, the resistance of the working electrode can be reduced if an additional thicker metal layer is coated on the optically transparent film in the region not exposed to the light beam under the insulation layer. If the insulation is prepared via lamination, a thin metal foil can be simply inserted instead of the deposited metal layer. This new cell design (Fig. II.6.5) enables cyclic voltam-mograms as well as current time curves in the case of a potential step experiment (chronoamperograms) simultaneously with a series of time-resolved spectra to be recorded. This experimental approach allows absorbance-potential or absorbance-time curves to be recorded to analyse the reaction kinetics of the generation of intermediates and the final product up to a time scale of approximately 0.1 s life-time. 

Figure 4. Chronoamperograms for the anodic dissolution of niobium in 52 48 AlCl3 NaCl at 190 °C. (a) Potential was stepped from I.IOV to values ranging from 1.12V to 1.19V in lOmV increments, (b) Potential was stepped from I.IOV to values ranging from 1.26V to 1.31V in lOmV increments.

Figure 5. (a) Sampled-current voltammograms for the anodic dissolution of niobium in 52 48 AlCls.NaCl at 190 °C. The current was measured at 1, 2, 3, 4 and 5 second intervals from the Figure 4 transients, (b) Charge density vs. step potential obtained by integration of Figure 4 chronoamperograms. 

FIGURE 6 Chronoamperogram for the oxidation of hydroquinone (10 mM) in 0.1 M KCl at a polypyrrole electrode doped with ferricyanide ion. (1) Before exchange with Cl". (2) After exchange with Cl". Potential of the polymer electrode stepped from 0.2 to 1.08 V versus the Ag/AgCl electrode. Area of the Electrode 1 cm. Film thickness 20 im. (With permission from VCH Publishers, Weinheim, Germany, Ref. 29.)... 

In this method, [37] an electrode at equilibrium is polarized by a small shift of potential, thus keeping a constant concentration of inserted atoms on the surface of the electrode. The DC can be calculated from the registered current-versus-time curve called chronoamperogram. The method is also called single-step chrono-amperometry (SSCAM). In this method, the condition D const is under better control than in the GSPM. 

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