Electrochemical AC impedance

Electrochemical AC impedance measurements provided another label-free approach to DNA hybridization detection on a DNA probe-doped polypyrrole film on MWCNT-modified electrodes... 

Electrochemical AC impedance methods are well suited for in situ monitoring of changes in surface roughness and capacitance [43), as discussed in Chapter 2.6 in... 

In typical Au MFC ET experiments with SAMs, the clusters are linked to a metal electrode surface through a self-assembled alkyl chain monolayer with specific linking sites. The electron is presumed to be transferred to/from the tethered MFC through the chain linker to/from the electrode surface. Techniques used to measure ET rates in Au MFCs attached to SAMs are potential step voltammetry and electrochemical AC impedance. Rate constants determined through impedance measurements have the virtue of less distortion due to uncompensated resistance. Also, rate constants determined using cyclic voltammetry are explicitly based on the kinetic behavior of the subpopulation of MFCs that produces the most prominent current peaks. Fotential step voltammetry resolves more peaks and thus gives a better indication of the diversity of rate constants of the redox species in the monolayer. ... 

Electrochemical Impedance Spectroscopy (EIS) and AC Impedance Many direct-current test techniques assess the overall corrosion process occurring at a metal surface, but treat the metal/ solution interface as if it were a pure resistor. Problems of accuracy and reproducibility frequently encountered in the application of direct-current methods have led to increasing use of electrochemical impedance spectroscopy (EIS). 

The apphcation of an impressed alternating current on a metal specimen can generate information on the state of the surface of the specimen. The corrosion behavior of the surface of an electrode is related to the way in which that surface responds to this electrochemical circmt. The AC impedance technique involves the application of a small sinusoidal voltage across this circuit. The frequency of that alternating signal is varied. The voltage and current response of the system are measured. 

A.D. Frantzis, S. Bebelis, and C.G. Vayenas, Electrochemical promotion (NEMCA) of CH4 and C2H4 oxidation on Pd/YSZ and investigation of the origin of NEMCA via AC impedance spectroscopy, Solid State Ionics 136-137, 863 (2000). 

In summary AC impedance spectroscopy provides concrete evidence for the formation of an effective electrochemical double layer over the entire gas-exposed electrode surface. The capacitance of this metal/gas double layer is of the order of 100-300 pF/cm2, comparable to that corresponding to the metal/solid electrolyte double layer. Furthermore it permits estimation of the three-phase-boundary length via Eq. 5.62 once the gas exposed electrode surface area NG is known. 

The use of a heavy arsenal of surface science (XPS, UPS, STM, AES, TPD) and electrochemical (cyclic voltammetry, AC Impedance) techniques (Chapter 5) showed that Equations (12.2) and (12.3) simply reflect the formation of an overall neutral backspillover formed double layer at the metal/gas interface. It thus became obvious that electrochemical promotion is just catalysis in presence of a controllable double layer which affects the bonding strength, Eb, of reactants and intermediates frequently in the simple form ... 

Measurements of electrochemical noise and AC impedance of coated metal substrates are under development (indeed have been used for quite some time). These measurements relate to the corrosion protection afforded by the coating and can, in principle, be made continuously. The complexity of the electrochemical reactions require sophisticated data analysis for extraction of useful information and relationships. 

Among a few electrochemical techniques available for studying the adsorption, the AC impedance technique has been most widely employed. Its high sensitivity to the physico-... 

This value represents the upper limit of a first order reaction rate constant, k, which may be determined by the RHSE. This limit is approximately one order of magnitude smaller that of a rotating electrode. One way to extend the upper limit is to combine the RHSE with an AC electrochemical technique, such as the AC impedance and faradaic rectification metods. Since the AC current distribution is uniform on a RHSE, accurate kinetic data may be obtained for the fast electrochemical reactions with a RHSE. 

One of the most powerful methods for the investigation of electrochemical reactions is the use of alternating current (AC) impedance techniques. In order to understand the basis of this approach, however, it is helpful first to consider some simple electronic analogues which mimic closely the systems of electrochemical interest. 

Studies on the adsorption of hydrogen from the gas phase had provided strong evidence for the existenee of two forms of adsorbed hydrogen and the AC impedance studies were supported by the results of the new LSV and CV techniques. The early measurements using the voltammetry methods were hampered by the use of impure electrolytes which resulted in ill-defined hydrogen adsorption and desorption peaks but the realisation of the need for a clean electrochemical system soon resulted in the routine observation of the now familiar twin Hads peaks. 

Unfortunately, impedance has amassed quite a few different names. For example, it is common now to see the acronym EIS , meaning electrochemical impedance spectroscopy. Strictly speaking, impedance is not a form of spectroscopy because the sample is not absorbing photons of any kind. A further linguistic problem is that AC impedance is tautologous since the word impedance itself implies an AC measurement. In this present discussion, we will simply say impedance . 

For an excellent introductory reading on ac impedance techniques for the purpose of ion conductivity measurement or study of interfacial properties, please see Linford, R. G. In Electrochemical Science and Technology of Polymers, 2nd ed. Linford, R. G., Ed. Elsevier Applied Science London, 1990 p 281. 

Electrochemical Characterization Technloues. Since corrosion Is an electrochemical process, It Is not surprising that a considerable amount of work has been reported over the years on electrical and electrochemical techniques for the study of the corrosion process. Leldhelser Ql.) and Szauer (12.> 11) have provided good reviews of the principal techniques. Walter has recently provided a review of DC electrochemical tests for painted metals (14). Both AC and DC methods have been employed to study a variety of Issues related to corrosion and corrosion protection. DC techniques are especially useful for studying substrate processes, while AC impedance techniques are most useful for studying processes relating to coated substrates and the performance of coatings. 

Akikusa J, Khan SUM (1997) Photo response and AC impedance characterization of n-Ti02 during hydrogen and oxygen evolution in an electrochemical cell. Int J Hydrogen Energy 22 875-882... 

Other Techniques - Other electrochemical techniques that could be employed in sensor technology would include potential-step methods (or chrono-amperometry, as current is recorded with time), current-step methods (or chronopotentiometry, as potential is recorded with time) and AC impedance. None of these techniques appear to have yet been applied to catalyst sensing in a systematic way. 

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... 

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