Electrochemical Mapping

Recently, two new electrochemical mapping techniques have become available the scanning vibrating electrode technique (SVET) and the localized electrochemical impedance spectroscopy (LEIS) technique. These techniques provide the capability to identify and monitor electrochemical behavior down to the micron level. These represent significant advances over traditional electrochemical methods (cyclic voltammetry, EIS, and even EQCM), which provide data that reflect only an average over the entire sample surface. Although such data are very useful, a major drawback is that no local or spatial information is obtained. 

SVET detects the electrochemical potential of a sample surface (with respect to a reference electrode) with a spatial resolution of tens of microns. The technique uses a probe tip that is rastered above the sample surface and then is oscillated perpendicular to the sample surface with an amplitude of 1-60 pm. 

In LEIS, the full electrochemical impedance spectrum of the sample/electrolyte interface can be obtained at the submillimeter level. The system works by stepping a probe tip across the sample surface (the smallest step size is 0.5 pm) while the sample (connected as the working electrode) is perturbed by an ac voltage waveform (usually about the open-circuit potential with an amplitude typically of 20 mV). The probe tip consists of two separated platinum electrodes, separated by a known distance. Measurement of the potential difference between the two electrodes allows the calculation of the potential gradients above the sample surface, which then give the current density. Comparison of the in-phase and out-of-phase current flow produces the impedance data, as with the regular EIS. The data can be plotted as Bode or Nyquist charts for specific points on the surface, or impedance maps of the sample surface can be obtained. 

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M. E., Macpherson, J.V., and Unwin, P.R. (2012) Electrochemical mapping reveals direct correlation between heterogeneous electron-transfer kinetics and local density of states in diamond electrodes. Angew. Chem. Int. Ed., 51(28), 7002 - 7006. 

Recently, two new electrochemical mapping techniques have become available the scanning vibrating electrode technique (SVET) and the localized... 

Apart from the traditional organic and combinatorial/high-throughput synthesis protocols covered in this book, more recent applications of microwave chemistry include biochemical processes such as high-speed polymerase chain reaction (PCR) [2], rapid enzyme-mediated protein mapping [3], and general enzyme-mediated organic transformations (biocatalysis) [4], Furthermore, microwaves have been used in conjunction with electrochemical [5] and photochemical processes [6], and are also heavily employed in polymer chemistry [7] and material science applications [8], such as in the fabrication and modification of carbon nanotubes or nanowires [9]. 

One of the most significant applications of STM to electrochemistry would involve the application of the full spectroscopic and imaging powers of the STM for electrode surfaces in contact with electrolytes. Such operation should enable the electrochemist to access, for the first time, a host of analytical techniques in a relatively simple and straightforward manner. It seems reasonable to expect at this time that atomic resolution images, I-V spectra, and work function maps should all be obtainable in aqueous and nonaqueous electrochemical environments. Moreover, the evolution of such information as a function of time will yield new knowledge about key electrochemical processes. The current state of STM applications to electrochemistry is discussed below. 

Figure 7. Detailed mapping of the dependence of ion conductivity on salt concentration (m), solvent composition (x), and temperature (7) in a commonly used binary solvent system EC/DMC by surface plots. The orientations, titles, and units of the axes used in the plots are shown in the bottom portion of the figure, and the temperatures for these plots are, in order of their appearance, from 60 to —30 °C in 10 °C increments. The o ranges for the surface plots are, in order of their appearance, (8.49, 16.7), (7.78, 14.6), (7.03, 12.6), (6.23, 10.6), (5.44, 8.7), (4.63, 7.00), (3.14, 5.47), (1.93, 4.14), (1.04, 3.00), and (0.46, 2.06) mS cm (Reproduced with permission from ref 195 (Figure 4). Copyright 2001 The Electrochemical Society.)...

Scheme 9.18 Top Plots of optical absorption intensity as a function of wavelength and electrode potential in the Sii region for K[h-NT]. In all plots, raw electrochemical data, that is, uncorrected for ohmic drop, are referenced to SCE. Bottom Chirality map displaying the average standard potentials associated to each SWNT. HiPco SWNTs are located inside the red line, while arc-discharge SWNT are inside the blue line. Starred values were extrapolated from the linear fitting equations given in the text. (See the color version of this Scheme in Color Plates section.)...

There is no doubt that if one looks at the whole of the electrochemical field around the century s end, cyclic voltammetiy has been the most frequently used technique. Indeed, it is the experiment with which all electrochemists begin their studies. It is a kind of road map or fingerprint for the experiment, indicating the potential region in which there is electrodic activity. Because of the very large scope of the technique, it is worth briefly describing its origin. 

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