Cyclic voltammetry data analysis

The cis/trans isomerization of cw-polyacetylene, previously only disclosed from spectroscopic data, has recently been detected by cyclic voltammetry The analysis of the redox data reveals that the trans-form is thermodynamically more favorable in the charged than in neutral state. 

Metal connectivity is advantageous. Transition metal characterization such as with electrochemical and microscopic analysis compliments standard organic -type methods (e.g., 13C and H NMR) and further enhances characterization of the large multidendri-tic structure(s). Cyclic voltammetry data strongly suggest the connection of branched structures.1821... 

Abstract. The characterization of cyclodextrin(CD) systems by electrochemical methods, mainly by cyclic voltammetry is discussed. The addition of CD to the electrolyte solution causes a decrease in the peak current and also a shift in the apparent half-wave potential in cyclic voltammetry. Quantitative analysis in the both phenomena affords the formation constants of CD complexes. The formation or dissociation rate constants can be evaluated from the cyclic voltammetric data at high scan rates. Adsorption of CD on the electrode surface is also mentioned. 

For the in situ characterization of modified electrodes, the method of choice is electrochemical analysis by cyclic voltammetry, ac voltammetry, chronoamperometry or chronocoulometry, or rotating disk voltametry. Cyclic voltammograms are easy to interpret from a qualitative point of view (Fig, 1). The other methods are less direct but they can yield quantitative data more readily. 

For the rapid electron transfer process, which follows a reversible chemical step (CE), a procedure is presented for the determination of chemical and electrochemical kinetic parameters. It is based on convolution electrochemistry and was applied for cyclic voltammetry with digital simulation [59] and chronoamperometric curves [60]. The analysis was applied to both simulated and experimental data. As an experimental example, the electroreduction of Cd(II) on HMDE electrode in dimethylsulphoxide (DM SO) [59] and DMF [60] with 0.5 M tetraethylammonium perchlorate (TEAP) was investigated. 

The electrochemical behavior of Np ions in basic aqueous solutions has been studied by several different groups. In a recent study, cyclic voltammetry experiments were performed in alkali ([OH ] = 0.9 — 6.5 M) and mixed hydroxo-carbonate solutions to determine the redox potentials of Np(V, VI, VII) complexes [97]. As shown in Fig. 2, in 3.1 M LiOH at a Pt electrode Np(VI) displays electrode processes associated with the Np(VI)/Np(V) and Np(VII)/Np(VI) couples, in addition to a single cathodic peak corresponding to the reduction of Np(V) to Np(IV). This latter process at Ep —400 mV (versus Hg/HgO/1 M NaOH) is chemically irreversible in this medium. Analysis of the voltammetric data revealed an electrochemically reversibleNp(VI)/Np(V)... 

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. 

Cyclic voltammetry is one of the most useful techniques for studying chemistry in lion-aqueous solutions. It is especially useful in studying electrode reactions that involve an unstable intermediate or product. By analyzing cyclic voltammograms, we can elucidate the reaction mechanisms and can determine the thermodynamic and kinetic properties of the unstable species. Some applications were described in previous sections. Much literature is available concerning cyclic voltammetry dealing with the theories and practical methods of measurement and data analysis [66]. In this section, three useful cyclic voltammetry techniques are outlined. 

It will be clear that cyclic voltammetry is a powerful tool for a first analysis of an electrochemical reaction occurring at the surface of an electrode because it will reveal reversibility. Depending on whether the system is reversible, information will be obtained about half wave potential, number of electrons exchanged in the reaction, the concentration and diffusion coefficient of the electroactive species. However, these data can also be obtained for an irreversible system1113 but, in this case, the equations describing the current-potential curves differ somewhat from Equations 2.21 to 2.27. 

DDPV curves is shown for spherical and disc electrodes and different AEf values. As can be seen, independently of the electrode size, a peak-shaped response is obtained with the same peak potential and width (see the superimposed A/pDPV/ A/[, 5 pyk — E curves in the inserted Figures) since these responses are independent of the electrode geometry (see Eqs. (4.173) and (4.176)). This is a notable advantage over Cyclic Voltammetry where sigmoidal curves are obtained when small electrodes are employed which makes data analysis more difficult and less... 

The chronocoulometry and chronoamperometry methods are most useful for the study of adsorption phenomena associated with electroactive species. Although less popular than cyclic voltammetry for the study of chemical reactions that are coupled with electrode reactions, these chrono- methods have merit for some situations. In all cases each step (diffusion, electron transfer, and chemical reactions) must be considered. For the simplification of the data analysis, conditions are chosen such that the electron-transfer process is controlled by the diffusion of an electroactive species. However, to obtain the kinetic parameters of chemical reactions, a reasonable mechanism must be available (often ascertained from cyclic voltammetry). A series of recent monographs provides details of useful applications for these methods.13,37,57... 

On the basis of an X-ray structure analysis [110], cyclic voltammetry [110] and MoBbauer data [111], BFC4 is best described as a zwitterion containing one cationic ferrocenyl substituent and a negative charge at boron [110]. 

Comparative anodic polarization data (Fig. 27) obtained by Conway and Liu (285-287) for chemically and anodically formed nickel oxide show a Tafel slope of 33 mV on anodically formed nickel oxide, lower than that for the chemically formed film (60 mV), with better activity than the former. Pseudocapacitance profiles obtained from an analysis of the potential relaxation data are shown in Fig. 28. The initial descending part of the C o versus rj profiles of Fig. 28a appears to be connected with the positive end of the well-known cyclic-voltammetry peak for Ni(II) - Ni(III) oxidation in nickel oxide. This peak goes into an ascending current versus potential line for O2... 

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