Platinum electrode impedance measurement

Transient measnrements (relaxation measurements) are made before transitory processes have ended, hence the current in the system consists of faradaic and non-faradaic components. Such measurements are made to determine the kinetic parameters of fast electrochemical reactions (by measuring the kinetic currents under conditions when the contribution of concentration polarization still is small) and also to determine the properties of electrode surfaces, in particular the EDL capacitance (by measuring the nonfaradaic current). In 1940, A. N. Frumkin, B. V. Ershler, and P. I. Dolin were the first to use a relaxation method for the study of fast kinetics when they used impedance measurements to study the kinetics of the hydrogen discharge on a platinum electrode. 

DNA immobilized by organosilane chemistries has proven to be an effective method for measuring impedance changes upon hybridization using both gold and platinum electrodes [21,50]. The effect of different silane chemistries creates differences in the hydrophobicity and hydration levels of the modified surface. The organosilane treatment along with the ssDNA... 

Proton conductive electrolyte properties of step 2 membranes were determined at 150°C by the impedance measurement using a 13-mm circular-plate-shaped platinum electrode. Testing results are provided in Table 1. 

So far, the ionic conductivity of most ILs has been measured by the complex impedance method [116], In this method, charge transfer between carrier ions and electrode is not necessary. Therefore platinum and stainless steel are frequently used as blocking electrodes. However, it is often difficult to distinguish the resistance and dielectric properties from Nyquist plots obtained by the impedance measurement. In order to clarify this, additional measurements using non-blocking electrodes or DC polarization measurement are needed. 

Electrical conductivity is easily determined by measuring the impedance of the sample in the low frequency range (see Section 22.6.3), but at a frequency above the range in which errors arise owing to electrode polarization effects. For example, measurement of the electrical conductivity of cream, which can be carried out by measuring the impedance between a pair of stainless steel or platinum electrodes immersed in the cream sample, should be done at a frequency of 105 Hz or higher (Lawton and Pethig, 1993). 

The conductivity of sintered pellets was obtained from two-probe impedance spectroscopy. Platinum electrodes were applied on both surfaces of pellets by coating platinum paste and then firing at 850°C for 0.5h. Measurements were made with an computer-interfaced impedance analyzer (GenRad 1689 Precision RLC Diglbridge) over a frequency range of 12-10 Hz in the temperature range of 500°C-800°C. Each sample was measured in air and H2 atmospheres, respectively. 

Peck et al. [153] carried out an experiment, which to date remains unique, on electrodes in the superconducting state. Unfortunately, instead of voltammetry, they used the less direct method of impedance measurements in the frequency range 10 -10 Hz. They studied two TBCCO microelectrodes (Tc 112 and 119K) and also (in test experiments) platinum and glassy carbon. All these electrodes were cathodically polarized under potentiostatic conditions (so that the amplitude of potential modulation was substantially lower than its constant component). The equivalent circuit included Cdi and the parallel polarization resistance. The nature of... 

Impedance samples of 13 mm diameter and 0.3 mm thickness were pressed in a die, mounted between platinum electrodes in an oven and the complex impedance measured between 10 Hz and 10 MHz. The spectra shown in Fig. 1 show a low frequency inter-particle relaxation (of no further interest to us) and an intra-particle relaxation associated with cation exchangeable sites. These relaxations have peak frequencies which exhibit the simple Ahrrenius behaviour shown in Fig. 2, ie... 

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. 

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. 

The associated counter and reference electrodes can either be included in the cell body or plumbed into the flow system separately. The cell designed by Meyer et al. [105] and used by Aoki et al. [104] incorporates both a platinum counter electrode and a silver pseudo-reference electrode within the channel unit. The cell shown in Fig. 31(a) contains a silver-silver chloride reference electrode in one of the ducts at the end of the channel. For a.c. impedance measurements, where ohmic drop must be minimised, this is... 

Ohmori, T., T. Kimura, and H. Masuda, Impedance measurements of a platinum cylindrical porous electrode replicated from anodic porous alumina. Journal of the Electrochemical Society, 1997. 144 p. 1286... 

The second technique involves using a four probe apparatus, similar to that described by Cahan and Wainright. The membrane sample is placed in an PTFE apparatus which is equipped with two platinum strips in contact with the film, as shown in Fig. 1.115. Two platinum electrodes in a fixed geometry (distance of 1.026 cm) were placed on the surface of the film to measure the membrane potential and capacitance. Conductivity measurements could be obtained by utilizing complex impedance plots, which employ a circuit diagram... 

In this context, platinised platinum (the same as that used for hydrogen reference electrodes, see section 1.4.1.2) is often used. When the contact area with the electrolyte increases, the double layer capacity increases substantially, when compared to the system s dielectric characteristics. The reason for this is that mean roughness is larger than the thickness of the double layer. In terms of impedance measurements, this leads to a broader frequency range in which the system s impedance is equal to the electrolyte s resistance. 

It is usually believed that high frequency capacitance obtained from impedance spectroscopy can represent ionic double layer capacity. However in general this is not the case for platinum electrode, this is the reason why one arrow in Fig. 1 (in the left) is crossed. In contrast to Cf measured under equilibrium conditions (by means of isoelectric potential shifts), non-equilibrium impedance response can contain a contribution from Ah (and/or Ao, surface concentration of oxygen-containing species). These contributions are determined by Ah and Ao potential derivatives and their free electrode charge derivatives, and in general can be either positive, or negative. 

The resistance of membranes can be measured by AC impedance methods [85,86], using the four-point-probe technique. The test membrane is placed in a cell consisting of two Pt-foil electrodes, spaced 3 cm apart, to feed the current to a sample of 3 x 1 cm and two platinum needles placed 1 cm apart, to measure the potential drop (see Fig. 4.3.26). The cell is placed in a vessel maintained at constant temperature by circulating water. The impedance measurements are then carried out at 1-10 kHz using a frequency-response analyzer (e.g., Solatron Model 1255HF frequency analyzer). After ensuring that there are no parasitic processes (from the phase angle measurements, which should be zero), one can measure the resistance directly. The membrane resistance can also be obtained directly from the real part of the impedance (see typical data in Fig. 4.3.27). 

Impedance is typically measured in a two-electrode configuration where the electrolyte is compressed between two blocking (steel, platinum) or nonblocking Li-electrodes (Qian et al. [2(X)2]). Analysis of electrolyte impedance in the presence of electrode impedance is complicated and usually assumes that the electrolyte is responsible for the highest frequency region of the spectrum, about IkHz. To improve confidence in the conductivity estimation, measurements with several layer thicknesses should be performed. To remove the effect of the electrode impedance in a test setup, four-electrode measurements have also been proposed (Bruce et al. [1988]). Typically, two pseudoreference electrodes made of Li-foil strips are pressed through a cavity in the middle of circular main electrodes to the surface of the polymer electrolyte under test. 

FIGURE 4 Bode plot of the impedance (a) magnitude and (b) phase of a microfabricated interdigated microsensor electrode array measured over the range 0.1 mHz to 100 kHz in 0.5 M KCl at 25°C. Showing the effect of electrode platinization ( ) unplatinized platinum electrodes ( ) platinized platinum electrodes. 

The electrical potential of the reaction mixture is measured with a platinum electrode and a Hg/Hg2S04 reference (available from Rainin). The output can be recorded on a single-channel strip chart recorder, with the platinum electrode attached to the positive terminal and the reference to the negative, or the recording can be made via a high-impedance input to an A/D board (analog-to-digital converter) on a computer (see Chapter 3). 

Fig. 9. Experimental setup for impedance measurements with electrochenucal control of membrane impedance platinized platinum electrodes (a) constant voltage power supply, (b) gold minigrid electrode (c) polypyrrole film, (d) 1 M KCl solution (e) constant current ac circuit, (f). At right is a microscopic view of membrane, illustrating effect of membrane potential on ionic resistance (reprinted with permission ft om Ref.

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