Electrode Reactions Complicated by Adsorption of the Reactant and Product

Electrode Reactions Complicated by Adsorption of the Reactant and Product 

SWV is a very sensitive technique partly because of its ability to discriminate against charging current [70-74]. However, a specific adsorption of reactant may significantly enhance SWV peak currents [75,76]. Unlike alternating current voltammetry, SWV effectively separates a capacitive current from a so-called pseudocapacitance [77]. This is the basis for an electroanalytical application of SWV in combination with an adsorptive accumulation of analytes [78-81]. 

A redox reaction of surface-active reactants can be divided in two groups  

The relationship between the stripping peak current of a fast and reversible mixed reaction and the square-wave frequency is a curve defined by Aip = 0, for /= 0, and an asymptote Aip = fc/+ z [90]. The intercept z depends on the delay time and apparently vanishes when t eiay s. Consequently, the ratio Aip// may not be constant for all frequencies. This effect is caused by the additional adsorption during the first period of the stripping scan. The stripping peak potential of a reversible mixed reaction depends linearly on the logarithm of frequency [89]  

The peak current depends on the square-wave amplitude E, and the potential increment AE in the same way as in the case of the simple reaction (Eq. II.3.1) (see Table II.3.1). The half-peak width also depends on the amplitude and has no diagnostic value. However, the response of the reversible reaction (II.3.5) is narrower than the response of the reversible reaction (Eq. II.3.1). If nE y = 50 mV and tiAE = 10 mV, the half-peak widths are 100 mV and 125 mV, respectively [88]. 

The relationship between the stripping peak current of a fast and reversible mixed reaction and the square-wave frequency is a curve defined by Atp = 0, for/= 0, and an asympfofe A/p = + z [90]. The intercept z depends on the delay time and 

Under the influence of elecfrode kinetics, the surface reaction (Eq. II. 3.4) depends on the dimensionless kinetic parameter K = ks/f (Eq. II.3.57) and the dimensionless adsorption parameters Uox=-S ox/ -Do and tired=-Kred/ -Dr (Eqs. II.3.58 and II.3.59) [89, 91-93]. Equations (II.3.50) and (II.3.53) are complicated by the diffusion of the redox species Ox and Red and their adsorption equilibria. The kinetic effects can be investigated separately by analyzing a simplified surface reaction (Eq. 11.3.64) that is a model of strong and totally irreversible 

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