Kinetics and Mechanism of Electrodeposition

When an electrode is made a part of an electrochemical cell through which current is flowing, its potential will differ from the equilibrium potential. If the equilibrium potential of the electrode (potential in the absence of external current) is E and the potential of the same electrode as a result of external current flowing is E I), the different tj between these two potentials, 

Mass transport processes are involved in the overall reaction. In these processes the substances consumed or formed during the electrode reaction are transported from the bulk solution to the interphase (electrode surface) and from the interphase to the bulk 

Fundamentals of Electrochemical Deposition, Second Edition. By Milan Paunovic and Mordechay Schlesinger Copyright 2006 John Wiley Sons, Inc. 

Chemical reactions can be involved in the overall electrode process. They can be homogeneous reactions in the solution and heterogeneous reactions at the surface. The rate constant of chemical reactions is independent of potential. However, chemical reactions can be hindered, and thus the reaction overpotential rj can hinder the current flow. 

Processes at metal/metal-ion electrodes include crystallization partial reactions. These are processes by which atoms are either incorporated into or removed from the crystal lattice. Hindrance of these processes results in crystallization overpotential The slowest partial reaction is rate determining for the total overall reaction. However, several partial reactions can have low reaction rates and can be rate determining. 

The overpotential 77 is required to overcome hindrance of the overall electrode reaction, which is usually composed of the sequence of partial reactions. There are four possible partial reactions and thus four types of rate control charge transfer, diffusion, chemical reaction, and crystallization. Charge-transfer reaction involves transfer of charge carriers, ions or electrons, across the double layer. This transfer occurs between the electrode and an ion, or molecule. The charge-transfer reaction is the only partial reaction directly affected by the electrode potential. Thus, the rate of charge-transfer reaction is determined by the electrode potential. 

Pure charge-transfer overpotential t]a exists only if the charge-transfer reaction is hindered and none of the other partial reactions is hindered. In this case the charge-transfer reaction is the rate-determining step. 

Mass transport processes are involved in the overall reaction. In these processes the substances consumed or formed during the electrode reaction are transported from the bulk solution to the interphase (electrode surface) and from the interphase to the bulk solution. This mass transport takes place by diffusion. Pure diffusion overpotential t]A occurs if the mass transport is the slowest process among the partial processes involved in the overall electrode reaction. In this case diffusion is the rate-determining step. 

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Rodrigues S, Munichandraiah N, Shukla AK (1998) A cyclic voltammetric study of the kinetics and mechanism of electrodeposition of manganese dioxide. J Appl Electrochem 28 ... 

There are four types of fundamental subjects involved in the process represented by Eq. (1.1) (1) metal-solution interface as the locus of the deposition process, (2) kinetics and mechanism of the deposition process, (3) nucleation and growth processes of the metal lattice (M a[tice), and (4) structure and properties of the deposits. The material in this book is arranged according to these four fundamental issues. We start by considering the basic components of an electrochemical cell for deposition in the first three chapters. Chapter 2 treats water and ionic solutions Chapter 3, metal and metal surfaces and Chapter 4, the metal-solution interface. In Chapter 5 we discuss the potential difference across an interface. Chapter 6 contains presentation of the kinetics and mechanisms of electrodeposition. Nucleation and growth of thin films and formation of the bulk phase are treated in Chapter 7. Electroless deposition and deposition by displacement are the subject of Chapters 8 and 9, respectively. Chapter 10 contains discussion on the effects of additives in the deposition and nucleation and growth processes. Simultaneous deposition of two or more metals, alloy deposition, is discussed in Chapter 11. The manner in which... 

Most theories of anomalous deposition in this case are based on the studies on kinetics and mechanism of electrodeposition of iron by Bockris et al. [66]. They proposed the following mechanism for the electrodeposition of Fe... 

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