Activation energy surface conduction

Nickel oxides prepared at 250 and 300° are alsop-type semiconductors (40). This means that, although the oxide surface has been reduced, the oxide phase still contains an excess of oxygen. Electrical conductivities and activation energies of conductivity are identical for NiO(200°) and NiO(250°) (ff2oo° X 10-1 ohm-i cm-i = 24kcal/mole) (41),... 

Catalyst Concentration of foreign ions (at.%) Surface area (m2/gm) Stoichiometric composition (at.%) Concentration of nickel" (at.% Ni) Electrical conductivity at 250° (ohm i cm ) Activation energy of conductivity (kcal/mole)... 

Higher activation energies for conductance in the more dilute solutions and with the smallest capillary diameters, as described by Schufle et al., are consistent overall with favorable conditions for electroosmosis. It would be of interest to compare the results of ac and dc methods for conductance of electrolytes in microcapillaries. Problems of defining the conductance of ions in double layer regions, as mentioned above, persist however. Also, the double layer Itself could have some structuring effect on surface water molecules. 

As the working temperature of the substrate was increased, the induction period (the delay time) of increased conductivity decreased due to increased rate of lateral diffusion of hydrogen atoms towards the sensor. The activation energy for surface migration of particles along a Si02 substrate estimated from the tilt of the Arrhenius plot was found to be about 20 kj/mol. 

By varying the temperature at which the experiments were conducted and the distance between the activator and the sensor, the data were obtained (Fig. 4.17) which allowed us to calculate the activation energy of migration of hydrogen adatoms (protium and deuterium) along the carrier surface and coefficients of lateral diffusion of hydrogen atoms appearing due to the spillover effect (see Table 4.2). 

Kim et al. [123] conducted the kinetic study of methane catalytic decomposition over ACs. Several domestic (South Korea) ACs made out of coconut shell and coal were tested as catalysts for methane decomposition at the range of temperatures 750-900°C using a fixed-bed reactor. The authors reported that no significant difference in kinetic behavior of different AC samples was observed despite the differences in their surface area and method of activation. The reaction order was 0.5 for all the AC samples tested and their activation energies were also very close (about 200 kj/mol) regardless of the origin. The ashes derived from AC and coal did not show appreciable catalytic effect on methane decomposition. 

Fig. 9-8. Potential energy profile for ionization of surface atoms in two steps on a covalent semiconductor electrode c, = band giq> energy tfi s electron level in an intermediate radical S " Ag = activation energy for the first step of radical formation in the conduction band mechanism df = activation energy for the first step of radical formation in the valence band mechanism = activation energy for the second step of radical ionization in the conduction band mechanism Ag = activation energy for the second step of radical ionization in the valence band mechanism beR = CR-Ev. [From Gerischer, 1970.]...

In general, the activation energy for the release of electrons from surface atoms into the conduction band increases with increasing band gap of the semiconductor electrode with this increase the capture of holes by the surface atoms and radicals predominates. Except for germanium, most covalent semiconductors have been found to dissolve anodically through this valence band mechanism [Memming, 1983]. 

Another semiconducting fulleride salt, [Ru(bpy)3](C5o)2 with bpy = 2,2 -bipyridine, crystallizes on the Pt electrode surface out of dichloromethane solutions saturated with [Ru(bpy)3]PF5 within a few minutes [79]. The NIR spectra of benzonitrile solutions of this salt demonstrate that the only fulleride anion present is 55 . The temperature dependence of the conductivity is typical for a semiconductor, with the room temperature conductivity being 0.01 S cm and the activation energy 0.1 kj mol (0.15 eV). It was postulated that there is an electronic overlap between the two ions of this salt leading to a donation of electron density from the 55 to the ligand orbitals in the [Ru(bpy)3] " AI 0.7) [79]. 

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