Electrochemical impedance measurements

In maldug electrochemical impedance measurements, one vec tor is examined, using the others as the frame of reference. The voltage vector is divided by the current vec tor, as in Ohm s law. Electrochemical impedance measures the impedance of an electrochemical system and then mathematically models the response using simple circuit elements such as resistors, capacitors, and inductors. In some cases, the circuit elements are used to yield information about the kinetics of the corrosion process. 

Neufeld, P. and Queenan, E. D., Frequency Dependence of Polarisation Resistance Measured with Square Wave Alternating Potential , Br. Corros. J., 5, 72-75, March (1970) Fontana, M. G., Corrosion Engineering, 3rd edn., McGraw-Hill, pp 194-8 (1986) Dawson, J. L., Callow, L. M., Hlady, K. and Richardson, J. A., Corrosion Rate Determination By Electrochemical Impedance Measurement , Conf. On-Line Surveillance and Monitoring of Process Plant, London, Society of Chemical Industry (1977)... 

As with alternating electrical currents, phase-sensitive measurements are also possible with microwave radiation. The easiest method consists of measuring phase-shifted microwave signals via a lock-in technique by modulating the electrode potential. Such a technique, which measures the phase shift between the potential and the microwave signal, will give specific (e.g., kinetic) information on the system (see later discussion). However, it should not be taken as the equivalent of impedance measurements with microwaves. As in electrochemical impedance measurements,... 

The combination of photocurrent measurements with photoinduced microwave conductivity measurements yields, as we have seen [Eqs. (11), (12), and (13)], the interfacial rate constants for minority carrier reactions (kn sr) as well as the surface concentration of photoinduced minority carriers (Aps) (and a series of solid-state parameters of the electrode material). Since light intensity modulation spectroscopy measurements give information on kinetic constants of electrode processes, a combination of this technique with light intensity-modulated microwave measurements should lead to information on kinetic mechanisms, especially very fast ones, which would not be accessible with conventional electrochemical techniques owing to RC restraints. Also, more specific kinetic information may become accessible for example, a distinction between different recombination processes. Potential-modulation MC techniques may, in parallel with potential-modulation electrochemical impedance measurements, provide more detailed information relevant for the interpretation and measurement of interfacial capacitance (see later discus-... 

Electrochemical impedance spectroscopy leads to information on surface states and representative circuits of electrode/electrolyte interfaces. Here, the measurement technique involves potential modulation and the detection of phase shifts with respect to the generated current. The driving force in a microwave measurement is the microwave power, which is proportional to E2 (E = electrical microwave field). Therefore, for a microwave impedance measurement, the microwave power P has to be modulated to observe a phase shift with respect to the flux, the transmitted or reflected microwave power APIP. Phase-sensitive microwave conductivity (impedance) measurements, again provided that a reliable theory is available for combining them with an electrochemical impedance measurement, should lead to information on the kinetics of surface states and defects and the polarizability of surface states, and may lead to more reliable information on real representative circuits of electrodes. We suspect that representative electrical circuits for electrode/electrolyte interfaces may become directly determinable by combining phase-sensitive electrical and microwave conductivity measurements. However, up to now, in this early stage of development of microwave electrochemistry, only comparatively simple measurements can be evaluated. 

At present, the microwave electrochemical technique is still in its infancy and only exploits a portion of the experimental research possibilities that are provided by microwave technology. Much experience still has to be gained with the improvement of experimental cells for microwave studies and in the adjustment of the parameters that determine the sensitivity and reliability of microwave measurements. Many research possibilities are still unexplored, especially in the field of transient PMC measurements at semiconductor electrodes and in the application of phase-sensitive microwave conductivity measurements, which may be successfully combined with electrochemical impedance measurements for a more detailed exploration of surface states and representative electrical circuits of semiconductor liquid junctions. 

J.P. Cloarec, N. Deligianis, J.R. Martin, I. Lawrence, E. Souteyrand, C. Polychronakos, and M.F. Lawrence, Immobilisation of homooligonucleotide probe layers onto Si/Si02 substrates characterisation by electrochemical impedance measurements and radiolabelling. Biosens. Bioelectron. 17, 405 112 (2002). 

E. Souteyrand, J.R. Martin, and C. Martelet, Direct detection of biomolecules by electrochemical impedance measurements. Sens. Actuators B 20, 63-69 (1994). 

With the aid of steady-state polarization and electrochemical impedance measurements in an ammonia containing solution maintained at pH = 9-10.5, Touhami et al. proposed the following mechanism for the H2PO2 reaction utilizing an intermediate adion, Ni,[ds [72] generated in the two step reduction of Ni2+ ... 

As suggested by Epelboin et al. [72] on the basis of electrochemical impedance measurements, Ni [ds may play more than one role in Ni electrodeposition, and by extension, similar roles in electroless deposition. It is worth briefly noting the reactions Epelboin et al. proposed in which a Ni [ds intermediate may be involved in ... 

ASTM G53-77, Salt Spray and Electrochemical Impedance Measurements). The results indicate that electrochemical impedance measurements provide a satisfactory correlation with the behaviour of paint coatings as evaluated by visual examination. In addition, it appears that, in certain cases, data obtained by this technique will allow prediction of the metallic corrosion underneath the paint coating when no changes in the appearance of the coating can be externally observed. 

Electrochemical impedance measurements of the physical adsorption of ssDNA and dsDNA yields useful information about the kinetics and mobihty of the adsorption process. Physical adsorption of DNA is a simple and inexpensive method of immobilization. The ability to detect differences between ssDNA and dsDNA by impedance could be applicable to DNA biosensor technology. EIS measurements were made of the electrical double layer of a hanging drop mercury electrode for both ssDNA and dsDNA [34]. The impedance profiles were modeled by the Debye equivalent circuit for the adsorption and desorption of both ssDNA and dsDNA. Desorption of denatured ssDNA demonstrated greater dielectric loss than desorption of dsDNA. The greater flexibility of the ssDNA compared to dsDNA was proposed to account for this difference. 

Recently, Darowicki [29, 30] has presented a new mode of electrochemical impedance measurements. This method employed a short time Fourier transformation to impedance evaluation. The digital harmonic analysis of cadmium-ion reduction on mercury electrode was presented [31]. A modern concept in nonstationary electrochemical impedance spectroscopy theory and experimental approach was described [32]. The new investigation method allows determination of the dependence of complex impedance versus potential [32] and time [33]. The reduction of cadmium on DM E was chosen to present the possibility of these techniques. Figure 2 illustrates the change of impedance for the Cd(II) reduction on the hanging drop mercury electrode obtained for the scan rate 10 mV s k... 

Impedance Spectroscopy for More Complex Interfacial Situations. The electrochemical interfacial equivalent circuits shown in Figs. 7.48 and 7.49 are the simplest circuits that can be matched to actual electrochemical impedance measurements. The circuit in Fig. 7.49 would be expected to apply to an electrode reaction that involves only electron transfer (e.g., redox systems of the type Fc3+ + e Fe2+), no adsorbed intermediate. 

Yang ZH, Wu HQ. The electrochemical impedance measurements of carbon nanotubes. Chem Phys Lett 2001 343 235-240. 

Practice for verification of algorithm and equipment for electrochemical impedance measurements. G 106 Annual Book of ASTM Standards 03.02, ASTM. 

Wegener J, Zink S, Rosen P, Galla H (1999) Use of electrochemical impedance measurements to monitor beta-adrenergic stimulation of bovine aortic endothelial cells. Pflugers Arch 437 925-934... 

Through the combination of SPR with a - poten-tiostat, SPR can be measured in-situ during an electrochemical experiment (electrochemical surface plasmon resonace, ESPR). Respective setups are nowadays commercially available. Voltammetric methods, coupled to SPR, are advantageously utilized for investigations of - conducting polymers, thin film formation under influence of electric fields or potential variation, as well as - electropolymerization, or for development of -> biosensors and - modified electrodes. Further in-situ techniques, successfully used with SPR, include electrochemical - impedance measurements and -+ electrochemical quartz crystal microbalance. 

Electrochemical impedance measurement is convenient and usually no extra instrument is needed since contemporary potentiostat, which is normally used in an ECP or ECMP system, tends to possess EIS function. However, the thickness of an anodic film cannot be easily determined from the measured impedance or impedance spectra because the electrical resistivity of the film is usually unknown. 

Electrochemical impedance measurements were also used to detect the hybridization of DNA on Si/Si02 chips and great emphasis has been put by Cloarec et al. [112] on the immobilization of single strands on the substrates in order to obtain reproducible sensors. The adsorption of dsDNA and nucleotides on a glassy carbon surface has also been evaluated by electrochemical impedance spectroscopy by Oliveira Brett et al. [113,114]. 

Electrochemical impedance measurements are often performed imder potentio-static regulation. In these measurements the potential is a fixed value with a superimposed (often sinusoidal) perturbation of fixed amplitude. This approach is attractive because, as discussed in Section 8.2.2, linearity in electrochemical systems is controlled by potential. 

P. T. Wojcik, P. Agarwal, and M. E. Orazem, "A Method for Maintaining a Constant Potential Variation during Galvanostatic Regulation of Electrochemical Impedance Measurements," Electrochimica Acta, 41 (1996) 977-983. 

On an Au/ITO electrode, Hb exhibited similar electrochemical behavior to Mb if Hb was immobilized on the electrode surface by casting the Hb solution thereon. However, when Hb was immobilized on Au/ITO by adsorption of Hb on a modified electrode, no direct voltammetric response for Hb could be seen. This was because the adsorption of Hb on the modified electrode did not provide a sufficient amount of protein. However, the adsorptive immobilization of Hb on a gold nanoparticle-modified ITO electrode could be observed by electrochemical impedance measurements using an [Fe(CN)6]37[Fe(CN)6]4 redox probe (Figure 14) [46], By the simulation program, the charge transfer resistance (Rt) value of bare ITO is estimated to be 77.43 kQ, which is decreased to 15.97 kQ after the gold nanoparticles... 

A three-electrode cell was used for the electrochemical impedance measurements, consisting of the working electrode, a platinum counter electrode, and a saturated calomel electrode (SCE). The electrolyte was 0.1 M sodium chloride. A Zahner-Electric IM6d impedance spectrometer was used for the impedance measurements. The impedance spectra were recorded at open circuit potential (OCP) in a frequency range from 0.1 Hz to 50 kHz with an AC amplitude of 10 mV. The thickness of the barrier film was calculated from the capacitance, a dielectric constant of 6.5 estimated from electrical measurement (see below) was used. 

Standard Practice for Verification of Algorithm and Equipment for Electrochemical Impedance Measurements, G 106-89, Annual Book of ASTM Standards, Vol 03.02, ASTM, 1995... 

---