Dynamic electrodes

Fisher A C 1996 Electrode Dynamics (Oxford Chemistry Primers) (New York Oxford University Press)... 

GAS PHASE, LIQUID PHASE AND ELECTRODE DYNAMICS IN DIMENSIONLESS FORM... 

Also, try Electrode Dynamics, by A. C. Fisher, Oxford University Press, Oxford, 1996, which is another title in the Oxford primer series. Its early chapters discuss the transport of analyte through solution and the various rates inherent in a dynamic electrochemistry measurement. It is a readily affordable and readable introduction and highly recommended. 

Electrode Dynamics (Fisher), mentioned above, contains a readable and affordable introduction to voltammetry and cyclic voltammetry. It is intended more for the chemist wanting mechanistic data rather than for the analyst. In addition, note that it does not explicitly cover polarography, although it does describe a few electrochemical techniques that are not included in this present book, so is still a useful text. 

Although not dealt with in this chapter, AC impedance measurements (sometimes called electrochemical impedance spectroscopy) are important in studying electrode dynamics. Generally in this method, a sinusoidal voltage (10 2 to 105 Hz) is applied to the cell, the phase angle and the amplitude of the response current are measured as a function of... 

Fisher, A. C. Electrode Dynamics, Oxford University Press, Oxford, 1996. 

The dynamics of the system are described by k°, with its units being s 1 for an adsorbed reactant. A redox couple with a large k° will establish the equilibrium concentrations given by the Nernst equation on a short timescale. Kinetically facile systems of this type require high-speed electrochemical techniques to successfully probe the electrode dynamics. The largest k° values that have been reliably measured are of the order of 106 s-1 and are associated with mechanistically simple reactions, i.e. there are no coupled chemical kinetics or significant structural differences between the oxidized and reduced forms. 

Miller, C.J., and Majda, M. 1988. Microporous aluminum oxide films at electrodes. Dynamics of ascorbic acid oxidation mediated by ferricyanide ions bound electrostatically in bilayer assemblies of octadecyltrichlorosilane and an octadecylviologen amphiphile. Analytical Chemistry 60. 1168-1176. 

Potential modulation techniques are used frequently in electrochemistry. The most well-known potential modulation electrochemical technique is a.c. impedance spectroscopy, in which current modulation caused by a potential modulation is analyzed. The potential modulation technique has also been used for in-situ IR spectroscopy (EMIRS and SNIFTIRS), but its use was aimed only to subtract the solution background and to enhance the S/N ratio of the spectram. If the IR signal caused by a potential modulation is analyzed, some information on electrode dynamics could be obtained as in a.c. impedance spectroscopy. 

Models that Neglect the Electrode Dynamic Response. Van t Riet (1979) and Gaddis (1999) suggest that if Tg < 3 s, the overall mass transfer coefficient can be accurately measured without model correction. Hence, assuming ideal mixing and insignificant gas-phase concentration changes, the overall mass transfer coefficient may be calculated from... 

Models Considering Membrane Diffusion and Time Delay. Lopez et al. (2006) and Vardar and Lilly (1982) suggested that when the electrode dynamic response was first order with a time delay, the following model can be used to correct the dissolved oxygen concentration data ... 

Available po electrodes are very slow in responding, and a measurement using the dynamic method results in significant errors. Many of the methods described in the literature to correct for gas and electrode dynamics are complicated and require a computer for calculations (Heineken, 1970 Lee and Tsao, 1979 Sobotka, Linek, and Prokop, 1973 Votruba and Sobotka, 1976). A simple method of evaluation that directly utilizes the response curve to a step function of the electrode and the aeration system is shown in Fig. 3.16 (Dang, Karrer and Dunn, 1977 Nikolaev et al., 1976). Use of this relative procedure allows the influence of the electrode to be eliminated even in viscous media. The influence of gas phase dynamics can be obtained from the area between the two curves, Equ. 3.50 (for the case of a maximally mixed gas phase in a well-stirred reactor vessel)... 

See, for example, Fisher AC (1996) Electrode dynamics. Oxford Univ Press, Oxford. 

A separate volume in the Oxford Chemistry Primers series is available to provide an introduction to kinetic electrochemistry (OCP 34, Electrode Dynamics by A. C Fisher). 

---