Surface properties enrichment factor

A lithium ion transference number significantly less than 1 is certainly an undesired property, because the resultant overwhelming anion movement and enrichment near electrode surfaces would cause concentration polarization during battery operation, especially when the local viscosity is high (such as in polymer electrolytes), and extra impedance to the ion transport would occur as a consequence at the interfaces. Fortunately, in liquid electrolytes, this polarization factor is not seriously pronounced. 

In the preceeding sections, development of the measurement technique and analysis of gas-phase characteristics in a slurry bubble column have been made along with some comparison of the experimental data with other correlations from the literature. Up to this point, analysis of gas-phase characteristics has included only single or binary liquid components. Recently, a large effect on gas holdup and bubble size has been observed for multicomponent liquid mixtures that contain small concentrations of surface-active species (24). In their study, mixtures of alcohols and water at alcohol concentrations less than 0.1 percent caused a dramatic increase in gas holdup (up to a factor of 2) and a decrease in bubble size (up to a factor of 4) compared to those observed for the water system. The authors think the effect is the result of- interaction between molecules of different species, leading to an enrichment of one species in the interface. Therefore, in multicomponent liquid mixtures, it is necessary to have knowledge of the presence of surface-active species as well as the physical properties of the fluid. 

The high value of the preexponential factor may be explained by a considerable change in the properties of the surface layer with temperature. An alloy containing 2.1 at.% Hg is nearly saturated at room temperature, while at a temperature of about 80°C, the solubility of mercury increases about 1.5 times[403]. Consequently, at increased temperatures, the alloy is far from saturation. We can therefore expect a lower surface concentration for mercury and higher for gallium. The enrichment of the surface by a metal with a lower overpotential increases (in absolute magnitude) the temperature coefficient of the overpotential, i.e. increases the activation energy and the preexponential factor. 

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