Electrodes growth rate

The properties of SEI electrodes, the growth rate of the SEI, the mechanism of dissolution and deposition, and the effects of various factors on SEI conductivity have been addressed elsewhere [1, 2] space limitations do not permit their repetition here. 

Galvanostatic, potentiostatic as well as potentiodynamic techniques can be used to electropolymerize suitable monomeric species and form the corresponding film on the electrode. Provided that the maximum formation potentials for all three techniques are the same, the resulting porperties of the films will be broadly similar. The potentiodynamic experiment in particular provides useful information on the growth rate of conducting polymers. The increase in current with each cycle of a multisweep CV is a direct measure of the increase in the surface of the redoxactive polymer and, hence, a suitable measure of relative growth rates (Fig. 5). 

For the special case of straight pores growing orthogonal to the electrode surface forming a flat interface to the bulk, the pore length l becomes equivalent to the layer thickness D. Equation (6.1) then also defines the growth rate of the whole porous layer rPS. The growth rate rPS of a porous layer depends on several... 

Having discussed the causes of pore wall passivity, we will now focus on the active state of the pore tip, which is caused by its efficiency in minority carrier collection. Usually the current density at the pore tip is determined by the applied bias. This is true for all highly doped as well as low doped p-type Si electrodes and so the pore growth rate increases with bias in these cases. For low doped, illuminated n-type electrodes, however, bias and current density become decoupled. The anodic bias applied during stable macropore formation in n-type substrates is... 

Fig. 9.9 SEM micrograph of an n-type silicon electrode with an etched macropore array (5 2 cm, (100), 3 V, 350 min, 2.5% HF). Pore growth was induced by a square pattern of pits produced by standard lithography and subsequent alkaline etching (inset upper right). In order to measure the depth dependence of the growth rate, the current density was periodically kept at 5 mA cm 2 for 45 min and then reduced to 3.3 mA crrf2 for 5 min. This results in a periodic decrease in the pore diameter, as indicated by the white labels on the left-hand side. After [Le9].

Galvanostatic, potentiostatic, or poten-tiodynamic techniques can be used to elec-tropolymerize suitable monomeric species and form the corresponding film on the electrode. The potentiodynamic experiment, in particular, provides useful information on the growth rate of conducting polymers. The increase in current with... 

Electrode reactions are analogous to the growth of tarnishing (corrosion) layers (Weppner and Huggins, 1977). Assuming that bulk transport is the rate determining step, the growth rate of the reaction product is inversely proportional to the instantaneous thickness L... 

This equation relates the growth rate of the electrode to the chemical... 

A theory concerning the electrode kinetics of all these shapes has been given (Popov, 1996). It is quite complicated and involves interactions of differing growth rates, the co-deposition of H, and of course the effects of diffusion, which is sometimes planar but is also spherical if the radius of curvature to which the ions diffuse is less than -0.01 cm. Much more may be done to increase the variety of these shapes and to control them if electrical variables are introduced (e.g., pulsing, superimposed ac, etc.). The area is open for much fascinating research. 

Li et al. [93] have used l-ethylimidazolium trifluoroacetate, which is a Bronsted acidic ionic liquid, as a medium for the electropolymerization of aniline. They report that in this ionic liquid the oxidation potential of aniline is lower (0.58 V compared to 0.83 V in 0.5 M H2SO4) and that the growth rate of the polymer is increased. Further, the resultant films are smooth, strongly adhered to the Pt working electrode and are very electrochemically stable. Similar results have been reported by Liu et al. [92], who found that this was the best ionic liquid for the polymerization of aniline, compared to the unsatisfactory results observed in other protic ionic liquids 1-butylimidazolium tetrafluoroborate, 1-butylimidazolium nitrate and 1-butylimidazolium p-toluenesulfonate, as well as the l-butyl-3-methylimidazolium hydrogen sulfate and l-butyl-3-methyimidazolium dihydrogen phosphate. 

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