Voltammetry half-peak width

Table 2.1 Square-wave voltammetry of fast and reversible electrode reaction (1.1). The dimensionless net peak current, the ratio of peak currents of the forward and backward components, the peak potentials of the components and the half-peak width as functions of SW amplitude ...

Half-peak-width — Also known as full-width-half-maximum (fwhm), peak width at half-height, Wi/2 When any experimental technique produces a peak that rises from and falls back to approximately the same base line, that peak may be characterized by its width at half the full height. In electrochemistry, the requisite peaks can be produced by -> cyclic voltammetry... 

DC) of a surface-confined redox process - at 298.2 K the half-peak-width for a reversible process is 90.6/n in mV where n is the number of exchanged electrons if there are no interactions between the adsorbed species (sites). In the case of attractive interactions is smaller, while at repulsive interactions its value is higher than 90.6 mV [i]. Peaks are also produced by AC and -> square-wave voltammetry of solution-based as well as surface-confined redox species, and by - stripping analysis and other techniques [i-iii]. 

The dimensionless net peak current A p primarily depends on the product nEsw [31]. This is shown in Table II.3.1. With increasing nfsw the slope BA pIdnEsv, continuously decreases, while the half-peak width increases. The maximum ratio between Ahalf-peak width appears for nEv, = 50mV [6]. This is the optimum amplitude for analytical measurements. If sw = 0, the square-wave signal turns into the signal of differential staircase voltammetry, and A[Pg.124]

Dopamine, epinephrine, norepinephrine, ascorbic acid 0.1 mol I, 1 phosphate buffer, pH 7.4. 6.0,4.4, 6.0, 6.8 Amperometry voltammetry Syringe pump straight tubular reactor peak width at half height measurements [73]... 

In cyclic voltammetry, an ideal (homogeneous) immobilized layer of molecules undergoing a reversible electron transfer that is uncomplicated by coupled chemical reactions gives a pair of reduction and oxidation peaks that are compact at all scan rates (the half-height width for a simple n-electron transfer is approximately... 

The voltammetry of surface-bound species is often found to exhibit non-ideal behaviour, in which the peak width at half peak height is not 90.6/n mV. Even under conditions where the peak position is not influenced by the scan rate, the peak-to-peak separation may still be non-zero. A large number of models have been proposed to explain these experimentally observed non-ideahties (see M.J. Honeychurch and G.A. Rechnitz, Electroanalysis 10 (1998) 285). 

The electronic adsorption spectra for the complexes [Ir(OH)6]", where n = 0-2, have been resolved and peak maxima locations, molar extinction coefficients, oscillator strengths, and band half-widths calculated.44 Bands have been assigned in the main part to be one-electron MLCT transitions. Spectrophotometrically determined rate constants for the OH reduction of the IrVI and Irv complexes at 25 °C in 3M NaOH are (2.59 0.09) x 10—3 s—1 and (1.53 0.05) x 10 4 s 1 respectively. The activation energy for the reduction, Irv—>IrIV, is nAkcalmoC1. Cyclic voltammetry and potentiostatic coulometry of [Ir(OEI )r,]2 in 3M NaOH on a Pt electrode show that during the electro-oxidation compounds of Irv and IrVI are formed.45... 

Equation (25) is general in that it does not depend on the electrochemical method employed to obtain the i-E data. Moreover, unlike conventional electrochemical methods such as cyclic or linear scan voltammetry, all of the experimental i-E data are used in kinetic analysis (as opposed to using limited information such as the peak potentials and half-widths when using cyclic voltammetry). Finally, and of particular importance, the convolution analysis has the great advantage that the heterogeneous ET kinetics can be analyzed without the need of defining a priori the ET rate law. By contrast, in conventional voltammetric analyses, a specific ET rate law (as a rule, the Butler-Volmer rate law) must be used to extract the relevant kinetic information. 

Differential Pulse Voltammetry (DPV). There are two main differences between differential pulse and NPV. The waveform for DPV, Figure 10(b), involves a pulse of amplitude AEpuise like that of the normal pulse sequence but the step back down is not to the initial potential, instead it is to a specific differential that is used during the measurement. Also, there are two sampling periods for each pulse, once at the end of the potential step up, like in NPV, and an additional sampling period at the end of the step down in potential, after which the difference in the two signals is recorded hence the name DPV. This pulse sequence results in a current signal response different from that of NPV, shown in Figure 10(b). If the electrochemical process is reversible, the peak half width, A p/2, is determined by equation (9), ... 

Fig. 9 Cycling voltammetry (5 mV/sec) for gold electrodes of different roughness [28]. SI untreated (as received) surface. S2-S4 surfaces obtained by electrodeposition of gold at currents densities close to the limiting current density. Inset approximate values of the half-width of resonance. Curves S2 and S3 lie between curves SI and S4, in some parts coinciding with them. Arrows P(S1) and P(S4), show the peak currents for reduction of the surface oxide, measured for the surfaces SI and S4, respectively. (From [28])...

The square wave voltammetry was more specially used to confirm the number of exchanged electrons of Si(IV) reduction, since the half-width of a peak is reliable to show the number of exchanged electrons with the following equation, cited in Ref. [7] ... 

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