Electrodeposition on the Inert Substrate

The formation of the first crystals during galvanostatic metal electrodeposition on an inert substrate is sometimes accompanied by a pronounced increase in overpotential [47, 48]. The dependence of the overpotential on time in such situations is shown in Fig. 2.16. 

Equations (2.131) and (2.132) are fulfilled in the initial stage of electrodeposition to the nuclei of metal formed on the inert substrate [112]. In this case, the nuclei behave as microelectrodes, because of their complete independent growth well before the formation of the diffusion layer of the macroelectrode. The radius Tq of the initial stable nucleus, at overpotential rj, is given by [117] ... 

Naturally, the same effect can be expected if some very fast electrochemical process, other than electrodeposition, occurs on the inert electrode partially covered by dendrites of active catalyst, especially if concentration of reacting ion is low.60 This could be of great importance for the activation of inert substrates for catalytic purposes. 

A surface metal film on an inert substrate is formed by the coalescence of growing grains developed from corresponding nuclei, as is illustrated in Fig. 2.21, whereby the surface properties of the inert substrate are changed to those of the electrodeposited metal. 

Electrodeposition was used to prepare a biaxially textured Gd2Zr207 (GZO) buffer layer on Ni-W substrates.129 Buffer layers provide chemically inert, continuous, and smooth bases for the growth of the superconductor oxide films. They also prevent both the diffusion of metal to the high-temperature superconductor (HTS) layer and the oxidation of the metal substrate when superconductor oxide films are processed at high temperature (-800 °C) in an oxygen atmosphere (100ppm or more). 

There are two basic problems in activation of inert substrates by electrodeposition first, the effect of the structure of the active surface film on the transformation of electrode from inert to active one7 and second, effect of the surface morphology on the polarization characteristics of activated electrodes.8,9 Obviously, in the last case, the nature of the initial substrate is not important. The analysis of both of them is the aim of this chapter. It will be performed for the cathodic reactions. Obviously, the corresponding analysis for the anodic processes can be performed in the similar way. 

Popov Kl, Krstajic NV (1983) The mechanism of spongy electrodeposits formation on inert substrate at low overpotentials. J Appl Electrochem 13 775-782... 

The confirmation of the above theories with accent on the analysis of the effect of exchange current density on the thin metal film formation on inert substrates can be obtained in the following way. In Chap. 1 (see Fig. 1.13 and Table 1.2) are given the polarization curves, the exchange current density values, and ijjio ratios for three different electrodeposition systems (Cd, Cu, and Ni) characterized by the substantially different value exchange current densities [13, 63]. 

Hence, a decrease in the value of the exchange current density of the deposition process enhances thin surface metal film formation on inert substrates due to an increase in the nucleation rate and a decrease in the radius of the zero nucleation zones. As a result of this, a compact surface metal film is formed with a smaller quantity of electrodeposited metal, and its coarseness and porosity decrease with a decreasing exchange current density. On the other hand, at sufficiently negative equilibrium potentials and low hydrogen overpotential for an inert substrate. 

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