Metal-electrolyte interface mass-transfer processes

If gaseous, electrochemicaUy active components of the measuring environment are not dissolved in the electrode, then the electrode process will consist of the following stages (also shown in Figure 1.18). They are adsorption-desorption of electrochem-icaUy active gaseous components on gas-electrolyte (GE) and gas-metal (GM) interfaces, ionization reaction (with electron transfer) on the metal-electrolyte (ME) and gas-electrolyte interfaces, and mass-transfer processes on all boundaries of three phases (gas-metal, gas-electrolyte, and metal-electrolyte). Furthermore, mass transfer of electrons and holes on the surface electrolyte layer may also occur. It is evident that the quantity of the current in the stationary state is equal to the quantity of the nonmetal component adsorbing on the gas-metal and gas-electrolyte surfaces as a result of ionization of this component on the ME and GE surfaces. 

There are two major factors which have to be considered in the process of electrochemical metal deposition. First, thermodynamics and growth properties of 2D Me and 3D Me phases can be treated in a similar manner to that for Me deposition from vapor or electrolyte phases. Second, the properties of the electrolyte phase strongly affect the structure of the substrate/electrolyte interface, the kinetics of the mass and charge transfer across it, and the kinetics of chemical reactions which can precede or follow the charge transfer. 

This system includes four elements Rs - resistance of 0.5M NaCl solution. Ret - electric charge transfer resistance for phase boundary of nickel - solution, CPEai - constant phase element characterizing the electrical properties of the double layer at the interface, and the element W - Warburg impedance, which characterizes the control of corrosion processes by diffusion of mass in the area of the electrolyte at the metal surface. 

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