Convolution voltammetry

The variation of a with potential according to equation (13) may also be used to estimate the value of E°, from which the value of D may be inferred. This approach has been applied to organic peroxides,44 including endoperoxides of biological interest.37 Here again, convolution voltammetry proved to be more precise than plain cyclic voltammetry. 

It is useful to briefly discuss some of the common and, perhaps, less common experimental approaches to determine the kinetics and thermodynamics of radical anion reactions. While electrochemical methods tend to be most often employed, other complementary techniques are increasingly valuable. In particular, laser flash photolysis and photoacoustic calorimetry provide independent measures of kinetics and thermodynamics of molecules and ion radicals. As most readers will not be familiar with all of these techniques, they will be briefly reviewed. In addition, the use of convolution voltammetry for the determination of electrode kinetics is discussed in more detail as this technique is not routinely used even by most electrochemists. Throughout this chapter we will reference all electrode potentials to the saturated calomel electrode and energies are reported in kcal mol. ... 

For dissociative electron transfer, an analogous thermochemical cycle can be derived (Scheme 2). In this case the standard potential includes a contribution from the bond fragmentation. Using equations (40) and (41) one can derive another useful expression for BDFEab-, equation (42). While direct electrochemical measurements on solutions may provide b. b, for example, of phenoxides and thiophenoxides (Section 4), the corresponding values for alkoxyl radicals are not as easily determined. Consequently, these values must be determined from a more circuitous thermochemical cycle (Scheme 3), using equation (43). The values of E°h+/h io a number of common solvents are tabulated elsewhere. Values of pKa in organic solvents are available from different sources. " A comparison of some estimated E° values with those determined by convolution voltammetry can be found in Section 3. 

Convolution is used in electrochemistry particularly as a means of converting the faradaic current /(f) into a more useful quantity. In this application, /(f) is most often convolved with 1 js/nt, this operation being identical with - semiintegration, but more complicated functions may also be used. See also -> convolution voltammetry, - deconvolution. 

Kinetic parameters of dimerization can be determined by polarography, -> chronoamperometry, -> linear potential scan and -> convolution voltammetry, -> rotating disc voltammetry, and alternating current sinusoidal polarography. See also -> association. 

For the elucidation of electrode mechanisms involving chemical steps various digital and analogous procedures are now the centre of attention. The fully automatized method applying artificial intelligence was presented in [5]. An expert system for the electrode mechanism is coupled to the electrochemical device. The presented set of rules allows identification of 10 mechanisms using cyclic voltammetry, chronocou-lometry, chronoamperometry and convolution voltammetry, respectively. 

A further advantage of the convolution method is that iR drop is very easily accounted for. In the case of conventional cyclic voltammetry, the nonlinearity of the sweep makes data analysis difficult however, in convolution voltammetry all that is necessary is to replace E by E + when plotting the voltammogram [43]. 

Electroanalytical Applications of Semiintegral and Convolution Voltammetry in Room-Temperature Ionic Liquids... 

In this chapter, the difhculties associated with applying conventional electroanalytical techniques, such as steady-state microelectrode voltammetry, RDE voltammetry, and dc cyclic voltanunetry with numerical simulation for the purpose of quantifying diffusivity in RTILs, are highlighted. In developing a strategy for overcoming these issues, we first outline the fundamentals of convolution voltammetry and then discuss a range of situations where electroanalytical applications of these techniques in RTILs have been employed successfully. 

The advantages of convolution voltammetry are illustrated in Fig. 5.8, obtained from the oxidation of [C2mim]I on a platinum microdisk electrode in [C2mim] [N(Tf)2]. In Fig. 5.8a, the shape of the voltammogram is intermediate between sigmoidal and peak-shaped, implying mixed planar/radial diffusion conditions. 

Fig. 5.10 Comparison of simulated (open circles) and experimental (solid line) cyclic voltam-mograms obtained from the oxidation of [Fe(Cp)2] (concentration determined by convolution voltammetry) in [C2mim][N(Tf)2] using a 25 pm diameter Pt microdisk electrode with scan rates of (from top to bottom) 100 and 50 mV s . The parameters used in the simulations were Drai = 4.49x 10 cm s, D x = 4.20x 10 cm s , c=0.0105 M, ks=10 cm/s, ro=0.00133 cm, a=0.5, r=296 K, and f " = 0.179 V. Reprinted with permission from Bentley et A., Anal. Chem. 2014, 86, 2073-2081 [15]. Copyright 2014, American Chemical Society...

Bentley CL, Bond AM, Hollenkamp AF, Mahon PJ, Zhang J (2014) Applications of convolution voltammetry in electroanalytical chemistry. Anal Chem 86(4) 2073-2081. doi 10.1021/ ac4036422... 

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