Electrical conductivity of activated

M. Pirani and E. Lax, and P. Comte. A. G. Worthing and R. Rudy observed the excitation of the line spectrum of tungsten and nickel by activated nitrogen and R. S. Mulliken, the excitation of the spectra of the copper halides. S. Karrer and co-workers examined the electrical conductivity of active nitrogen and... 

Industrial supercapacitors are essentially based on nanoporous carbon electrodes. The reasons of the choice lie in the high availability, low cost, chemical inertness, and good electrical conductivity of activated carbons, as well as a high versatility of texture and surface functionality. For these reasons, this chapter will present the capacitance properties of carbon-based electrodes showing optimization strategies playing on the structure/nanotexture of carbon and the nature of the electrolyte. 

Barroso-Bogeat A, Alexandre-Franco M, Femandez-Gonzalez C, Sanchez-Gonzalez J, Gomez-Serrano V (2015) Temperature dependence of DC electrical conductivity of activated caibon-metal oxide nanocomposites. Some insight into conduction mechanisms. J Phys Chem Solids 87 259-270... 

Electrochemical measurements are commonly carried out in a medium that consists of solvent containing a supporting electrolyte. The choice of the solvent is dictated primarily by the solubility of the analyte and its redox activity, and by solvent properties such as the electrical conductivity, electrochemical activity, and chemical reactivity. The solvent should not react with the analyte (or products) and should not undergo electrochemical reactions over a wide potential range. 

Methane decomposition is the most important reaction step, especially for high-temperature operations. Thus, carbon deposition occurs commonly and is a major problem, especially with the Ni-based anode. However, carbon deposition may not deactivate the anode [10, 11]. In some cases, the anode activity increases due to carbon deposition whieh increases the electrical conductivity of the low-Ni-content anode [II]. 

The comparison of experimental data on adsorption of various particles on different adsorbents indicate that absorbate reaction capacity plays a substantial role in effects of influence of adsorption on electric conductivity of oxide semiconductors. For instance, the activation energy of adsorption of molecular oxygen on ZnO is about 8 kcal/mole [83] and molecular hydrogen - 30 kcal/mole [185]. Due to such high activation energy of adsorption of molecular hydrogen at temperatures of adsorbent lower than 100 C (in contrast to O2) practically does not influence the electric conductivity of oxides. The molecular nitrogen and... 

The contacts of the third type (see Fig. 2.2, a) which are interfaces or contact areas separate microcrystals are equivalent (this has been shown in preceding Section) to the double Shottky barrier or, to put it more correctly, to the isotype heterotransitions [22, 29]. As it has been shown in Section 1.10 in detail, the energy of activation of electric conductivity of the material with dominant fraction of contacts of this type is dependent on the heights of intercrystalline barriers. The change in electric conductivity due to effects of various external effects (adsorption in particular) is related to the height of these barriers. 

The fair agreement of expressions (2.67) and (2.71) with experimental data as well as agreement of independently obtained experimental data concerning kinetics of the change of a with the data on equilibrium enabled the author of paper [89] to conclude that the proposed mechanism of effect of hydrogen on electric conductivity of semiconductors can be one of active mechanisms. The heat of total reaction (2.63) calculated from the values found was about 4.6 kcal. 

The low energy of activation of the change in electric conductivity of zinc oxide observed during adsorption of H-atoms ( 0.08 eV) [102] can correspond to the ionization energy of (0-H) -groups formed during direct interaction of H-atoms with O -ions of the lattice. 

Thus, the rigorous solution of kinetic equation describing the change in electric conductivity of a semiconductor during adsorption of radicals enables one to deduce that information on concentration of radicals in ambient volume can be obtained measuring both the stationary values of electric conductivity attained over a certain period of time after activation of the radical source and from the measurements of initial rates in change of electric conductivity during desactivation or activation of the radical flux incident on the surface of adsorbent, i.e. 

The opposite change in electric conductivity of adsorbent occurs during adsorption of such active particles as atoms of hydrogen and atoms of metals [115, 124,125]. The similar result is obtained during radiolysis of hydrocarbons [126] due to formation and chemisorption of H-atoms. Both the rate of adsorption caused change in electric conductivity and the value of its stationary values are determined in this cases by all the processes accompanying chemisorption [127],... 

In Chapter 3 we will provide experimental verification of expression obtained in this Section linking the concentration of active particles in ambient volume with the change in electric conductivity of adsorbent under stationary and kinetic conditions as well as experimental prove of validity assumptions made while deriving above expressions. 

The adsorption of particles of various type results in the change in electric conductivity of such bridges mainly due to local chemical interaction of adsorbed particles with electrically active defects which are electron donors and resulting, thereby, in decrease of their concentration or, on the contrary, in increase due to creation of new defects of this type. In both cases as it has been shown above there are substantially straightforward and easily verified relationships linking both the initial rates in the change of electric conductivity and the stationary values reflecting concentration of adsorbed particles in ambient volume. 

NH2 radicals, hydrogen atoms adsorbed on the surface of a semiconductor sensor more actively affect the electric conductivity of the sensor. 

This radicals do not escape from the surface (this is indicated by a semiconductor microdetector located near the adsorbent surface) undergoing chemisorption on the same semiconductor adsorbent Him. Thus, they caused a decrease in the electric conductivity of the adsorbent sensor, similarly to the case where free radicals arrived to the film surface from the outside (for example, from the gas phase). Note that in these cases, the role of semiconductor oxide films is twofold. First, they play a part of adsorbents, and photoprocesses occur on their surfaces. Second, they are used as sensors of the active particles produced on the same surface through photolysis of the adsorbed molecular layer. 

Note that this method enables one to observe variation of electric conductivity of a sample due to adsorption of hydrogen atoms appearing as a result of the spillover effect, no more. In a S3rstem based on this effect it is rather difficult to estimate the flux intensity of active particles between the two phases (an activator and a carrier). The intensity value obtained from such an experiment is always somewhat lower due to the interference of two opposite processes in such a sample, namely, birth of active particles on an activator and their recombination. When using such a complicated system as a semiconductor sensor of molecular hydrogen (in the case under consideration), one should properly choose both the carrier and the activator, and take care of optimal coverage of the carrier surface with metal globules and effect of their size [36]. 

Fig. 4.17. Kinetics of variation of electric conductivity of ZnO sensor following leaking-in H2 into the reaction cell and subsequently pumping it out (indicated by pointer) before (curve /) and after O - 4) activation of the working plate with palladium 0pj = 510 5 cm 2, = 6.7 Pa, T = 295 K O), 378 K (3),...

Fig. 4.18. Kinetics of variation of electric conductivity of the ZnO sensor on Si02 plate activated with Pd after leaking-in hydrogen 1 - without illuminating the plate 2 - during illumination with light at 313 nm from a mercury lamp with an additional water filter absorbing IR radiation. Stars show the beginning of sharp rise of electric conductivity.

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