Near-electrode layer

The kinetics of electrode processes on Cd electrode of an alkaline accumulator in dependence on changes in concentration of cadmium species in near-electrode layer of electrolyte was studied [343]. 

La203 and CuO [384,385]. In this case, the charge consumed per molecule a fortiori amounts to less than one electron and corresponds formally to partial oxidation of the copper. This process is extremely sensitive to the melt composition and leads to the desired product only in the complete absence of water. The kinetics of the process is determined, according to the authors, by the diffusion of lanthanum hydroxo complexes. In acid (moist) melts, the oxygen evolution is apparently accelerated on the anode, and this enhances the acidity locally in the near-electrode layer and causes the precipitation of CuO. 

Synthesis of Hydroxide Precursors by Varying the pH of the Near-Electrode Layer... 

In cases where the electrode surfaces differ insignificantly and a one-to-one correspondence between them can be reached, the hydrodynamic velocity components normal to the electrode surfaces are negligibly small and the electrical field in the IEG is quasi-homogeneous (except for the near-electrode layers). In this case, the local, one-dimensional approximation method is used. 

To calculate the transfer processes in the I EG, the boundary-layer approximation is used. According to it, the current density in the bulk IEG is calculated on the basis of the height-average mass-, momentum-, and energy-transfer equations and those in the near-electrode layers. The transfer in the diffusion layers is calculated similarly to the case of quasi-steady-state approximation. 

It is very clear from previous consideration that the proposed concept can be applied and for the case of electrodeposition of nickel. This concept is usable for all cases where there is the change of the hydrodynamic conditions in the near-electrode layer, which can be induced by the agitation of electrolyte by evolving hydrogen, ultrasonic and magnetic helds, or simply by vigorous stirring of an electrolyte. 

Finally, the analysis of the break-off diameter (or the diameter of the detached hydrogen bubble) can give an explanation why the change of hydrodynamic conditions in the near-electrode layer is achieved from the copper solution with the lower quantity of evolved hydrogen (i.e. from 0.15 M Q1SO4 in 0.50M H2SO4 at 800 mV... 

The second cause for the formation of passivating layers may be the polymerization of the solvent itself under the action of solvated electrons in the near-electrode layer of solution. Polymerization is particularly typical of compounds with P—Cl bonds which may be present as impurities in hexamethylphosphotriamide. 

The strongest argument adduced in favour of a hydrated electron as an intermediate in cathodic hydrogen evolution is the statement of Walker that in electrolysing an aqueous solution using a polished silver cathode he succeeded in observing optical absorption in the near-electrode layer, caused by a hydrated electron. However, later it was shown 215,219) reliable proofs of the... 

Response of water might be probable initial event of an organism s response to mild exposure this is probably connected to high sensitivity of oxidation-reduction processes in water media to action of external factors. Such features as electronic work function, zero charge potential, electrode potential, etc. are connected to concept of electrochemical processes. For this reason, the structure of near-electrode layer will depend on nature of electrodes material and specific nature of its interaction with solvent [8]. 

Of course, hydrogen evolution affects mechanism of formation of powder particles. The dendrites are formed without, as weU as with, a quantity of evolved hydrogen (the case of Cu) which was insufficient to achieve any effect on the hydrodynamic conditions in the near-electrode layer. Then, the electrodeposition process was primarily controlled by the diffusion of ions to the electrode surface, rather than the kinetic of the electrodeposition [5,6], The cauUflower-Uke particles are formed in the conditions of vigorous hychogen evoluticMi with the strong effect of evolved hydrogen on the hydrodynamic conditions in the near-electrode layer, and the concept of effective overpotential is proposed to explain formation of these particles [25, 35]. 

Anyway, the concept of effective overpotential can be summarized as follows when hydrogen evolution is vigorous enough to change hydrodynamic conditions in the near-electrode layer, then electrodeposition process occurs at some overpotential which is effectively lower than the specified one. This overpotential is denoted by effective overpotential of electrodeposition process. From morphological point of view, it means that morphologies of metal deposits become similar to those obtained at some lower overpotentials where there is no hydrogen evolution or it is very small. More about the formation of the honeycomb-like structure and the concept of effective overpotential can be found in [46, 52-61]. 

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