Adsorption impedance absorption

Moisture analyzers include a large variety of designs listed here. The list includes their inaccuracies (1) electrolytic hygrometer (2-5% FS), (2) capacitance (3% FS), (3) impedance (3% FS), (4) piezoelectric (10% AR or 2 ppm by volume), (5) heat of adsorption, (6) infrared (0.5-1% FS), (7) microwave (for a 1-15% moisture range, error is within 0.5%, less if corrected for density), (8) Karl Fischer titrator (0.5-1% FS), (9) drying oven (0.5-1% FS), (10) dipole, (11) cavity ring down, (12) fast neutron (0.2% in solid s density corrected), and (13) radio-frequency absorption (5 ppm). 

Among the various models ° " proposed in order to explain two-arc behavior in the Nyquist plot for the insertion electrode, the simple equivalent circuit " depicted in Figure 10(b) was used to analyze the impedance spectra. Flere, / ,. is the sum of the electrolyte and conducting substrate resistances Ream is the resistance associated with the particle-to-particle contact among the oxide particles Ccom is the contact capacitance due to the accumulation of charged species at the surface of the oxide particles Rat is the resistance associated with the absorption reaction of adsorbed lithium into the oxide and Cad represents the capacitance arising from the adsorption of lithium in the near-surface region of the oxide. 

Fig. 7.7 Electrical equivalent circuit for faradaic impedance of direct hydrogen absorption in presence of hydrogen adsorption-evolution...

Very often hydrogen absorption is studied at potentials before hydrogen evolution, especially in the HUPD zone [282—285], In such cases, the circuit becomes simplified because / p = oo and parameter B = —AC. The faradaic impedance in the case of indirect adsorption-absorptiOTi mechanism becomes... 

A. Lasia, Applications of electrochemical impedance spectroscopy to hydrogen adsorption, evolution and absorption into metals, in Modern Aspects of Electrochemistry, vol. 35, ed. by B.E. Conway, R.E. White (Kluwer/Plenum, New York, 2002), p. 1... 

Based on that knowledge, the impedance of electrode processes in the presence of diffusion in various geometries and adsorption is mathematically developed. This leads to the general method of determining the impedances of complex mechanisms. As an illustration, the impedance of electrocatalytic reactions involving hydrogen adsorption, absorption, and evolution is presented. 

It is difficult to present all applications of EIS some applications (such as those to solid materials and PEM fuel cells, corrosion and passivity, batteries see Sect. 1.3) may be found in available books. As examples, Mott-Schottky plots obtained for semiconductors, the impedance of coating and paints, and electrocatalysis of hydrogen adsorption, absorption and evolution were presented as they are well known in the electrochemical literature. Additionally, newer and developing applications such as the impedance of self-assembled monolayers, biological bilayers, and biosensors were also shown. 

Commonly used spectroscopic or analytical techniques for characterizing surfaces and coating layers on porous silicon are Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, energy dispersive X-ray spectrometry, fluorescence spectroscopy, UV-Vis absorption/reflectance spectroscopy, thin film optical interference spectroscopy, impedance spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, ellipsometry, nitrogen adsorption/desorp-tion analysis, and water contact angle. 

Some inferred data, regarding the role of Sn ions in the absorption processes, can be taken from the comparison of the impedance spectra obtained in the presence and in the absence of Sn(II). Impedance characteristics in Sn(II)-free solutions (Figure 8.41) are far from those typical of ideally polarizable electrodes and large frequency dispersion is observed. Similar behavior was also observed in tin systems involving specific adsorption of polyethers and other surfactants [100,... 

Two semicircles appear in the case of hydrogen adsorption or desorption limitations coupled with evolution only (without absorption or diffusion limitations), which are related to two time constants, charge transfer and adsorption R g or desorption impedance... 

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