Three dimensional voltammetry

Three dimensional voltammetry unites three conventional electrochemical techniques, classical polarography, pulse polarography and chronoamperometry into one very powerful experimental approach. 3D Voltammetry possess all the advantages of these methods without inheriting their limitations. Classical polarography and pulse polarography can be used to get a feel of the electrochemical behavior of a new system but both techniques suffer from a restricted time window. Both techniques discard much of the information contained in the i-t curve from each drop. Chronoamperometry possess an extended time window. However this technique can be applied once the reaction mechanism has been definitely established by some other technique, since a chronoampero-metric curve has the form of a falling transient and information is only obtained by a detailed mathematical analysis of its shape. 3D Voltammetry combines an extended time window and convenience in the analysis and interpretation of the experimental results. With 3D Voltammetry any... 

Figure 10. Three-dimensional AFM images of (a) Pt/polished AI2O3, (b) Pt/etched Ni, and (c) Pt/unpolished AI2O3 electrodes. Reprinted from J. -Y. Go et al., A study on ionic diffusion towards self-affine fractal electrode by cyclic voltammetry and atomic force microscopy, J. Electroanal. Chem., 549, p. 49, Copyright 2003, with permission from Elsevier Science.

The evidence that the 1 couple can diffuse freely in the liquid domains entrapped by the three-dimensional network of the gelators has also been found in the case of a PVDF-HFP gel via steady-state voltammetry at ultramicroelectrodes. Quite surprisingly the voltammogramms of the liquid and of the gel are almost perfectly superimposable (Fig. 17.14) and the diffusion coefficient of the redox ions could be calculated to be 3.6 x 10 cm2/s and 4.49 x 10-6 cm2/s for I- and I3, respectively, using Equation 17.15,... 

Normalized potential sweep voltammetry (NPSV) involves a three-dimensional analysis of the LSV wave where the normalized current (I/Ip) is taken as the Z axis, theoretical electrode potential data as the X axis, and experimental electrode potential data as the Y axis, with the potential axes defined relative to Ep/2. The method is illustrated by the voltammogram in Fig. 15. The projection of the wave on to the X—Y plane results in a straight line of unit slope and zero intercept if the theoretical and experimental data describe the same process. In practice, NPSV analysis simply involves the linear correlation of experimental vs. theoretical electrode potentials at particular values of the normalized current. 

The information that can be obtained with electrochemical detectors is not restricted to quantification. Instead of the conventional use of electrochemical detectors in amperometric mode at fixed potential, electrode arrays with each electrode held at different values of fixed potential can be used, in order to build up chronovoltammograms, three-dimensional current-voltage-time profiles. A 32-microband electrode array has been described for this purpose and applied to phenolic compounds [17] and which permits studying the electrode reaction mechanism at the same time as identification and quantification are carried out. Alternatively, fast voltammetric techniques such as fast-scan cyclic voltammetry or square wave voltammetry can be used to create chronovoltammograms of the eluted components. 

Figure 2.4 Voltammetry demonstrating that a self-assembled Cn6-alkane thiol film effectively blocks nickel electrodeposition on a copper substrate. The inset shows that patterning methods, such as soft lithography, may be used to produce three-dimensional topographies by through-mask plating using an alkanethiol layer as a resist [96],...

Cafiete et al. have recently elaborated on this approach by implementation of normal and derivative cyclic voltammetry. Pointing out that these types of three-dimensional analytical information is very powerful indeed (being similar to that provided by image detectors such as diode arrays), offering, besides theoretical studies, interesting practical possibilities especially in the multidetection of electroactive compounds, the authors used their cyclic... 

The difference Em - E is related to the binding energy of the first monolayer. In cyclic voltammetry this is the difference between the potentials of the most positive peak and the peak corresponding to the three-dimensional metal phase. The latter difference is linearly correlated with the difference of work functions of the deposited metal and the electrode material [11] ... 

AuE gold electrode CCPE chitosan-entrapped carbon paste electrode CV cyclic voltammetry 3D-CPNE three-dimensional conducting polymer nanorods electrodes DPASV differential pulse anodic stripping voltammetry DPV differential pulse voltammetry GCE glassy carbon electrode SPE screen-printed electrode SWV square wave voltammetry. 

Two-dimensional surface processes also give rise to a current vs. potential curve in cyclic voltammetry having a maximum but the curves are distinguished from those for diffusion-controlled processes by a dependence of the currents on the first power of the sweep rate, while the latter processes give currents related to square root of sweep rate. Coupled chemical steps give similar behavior with respect to changing sweep rate and type of mechanism as do the diffusion-controlled processes except that the curves exhibit maxima determined by depletion of the two-dimensional adlayer rather than the three-dimensional diffusion layer. The characteristic behavior found... 

One of the characteristics of microelectrodes is an enhanced rate of mass transport of reactants and products to and from the electrode surface. Nonlinear diffusion prevails at microelectrodes two-dimensional diffusion at microcylinder or microband electrodes and three-dimensional diffusion at microspherical and microdisk electrodes. The enhanced mass transport at microelectrodes, which is often called the edge effect, causes increased current density and results in steady-state current responses at sufficiently slow potential sweep rates in potential sweep voltammetry, as will be illustrated in section 3. 

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