Consecutive Electrochemical Reaction

Bockris JOM (1956) Kinetics of activation controlled consecutive electrochemical reactions anodic evolution of oxygen. J Chem Phys 24 817-827... 

IV. SEQUENCE OF CONSECUTIVE ELECTROCHEMICAL REACTIONS INVOLVING A SINGLE RATE-DETERMINING... 

Scheme 2. Consecutive electrochemical reaction scheme involving a dissociation step occurring before the rds...

The present notation, while requiring a distinction between combination and dissociation cases, shows clearly and specifically how the type of mechanism involved determines the transfer coefficients. In addition, substituting v= 1 into either of the above coefficients [Eq. (62) or (63)] reduces them to those for a simple consecutive electrochemical reaction, Eqs. (33a) and (33b). 

Recently, our group developed and validated a reactor model suitable for design calculations in a thin-gap single-pass high-conversion electrochemical cell [23, 24). The model is based on electrolyte plug flow and includes electrochemical kinetics and mass transfer limitations. It has been developed for the case of three consecutive electrochemical reactions, with the key product formed by the second reaction, but can easily be modifled in order to be used for other reaction schemes, such as parallel reactions or solvent oxidation. 

Berwick, A. The Study of Simple Consecutive Processes in Electrochemical Reactions 5... 

In Chapter 6 we considered the basic mles obeyed by simple electrode reactions occurring without the formation of intermediates. However, electrochemical reactions in which two or more electrons are transferred more often than not follow a path involving a number of consecutive, simpler steps producing stable or unstable intermediates (i.e., they are multistep reactions). 

The simplest type of complex electrochemical reactions consists of two steps, at least one of which must be a charge-transfer reaction. We now consider two consecutive electron-transfer reactions of the type ... 

One important type of complex mechanism in electrode reactions is a series of consecutive reactions. One example of this type is electrochemical deposition from complexed ions. In this case the electrochemical reaction is preceded by a chemical reaction. Another example is that of inclusion of cathodic hydrogen evolution. We discuss these two cases next. 

The catalytic pathway consists of a consecutive heterogeneous electrochemical reaction ... 

It differs, thereby, from simple redox reactions such as Fe3+ + e Fe2+. Such reactions do not involve an intermediate radical and lack consecutive steps and alternative pathways. Study of their kinetics, therefore, omits characteristics of most electrochemical reactions met, e.g., in electrochemical synthesis, energy conversion and storage, or corrosion. 

There is nothing unique about the determination of the mechanism of electrochemical reactions. Electrochemical kinetics is a parallel field to that of heterogeneous chemical kinetics and basically the mechanism tasks in the two related fields are the same. There are three goals that must be reached consecutively. 

Multi-electron (multistep) electrode processes will be studied in Sect. 3.3, underlining the key role of the difference of the formal potentials between each two consecutive electrochemical steps on the current-potential curves and also the comproportionation/disproportionation reactions that take place in the vicinity of the electrode surface. In the case of two-step reactions, interesting aspects of the current-potential curves will be discussed and related to the surface concentrations of the participating species. 

Electrochemical reactions on electrodes involve consecutive reactions with several steps. Knowledge of the reactants and products in each step may provide a valuable piece of evidence by means of which the pathway—and sometimes even the rate-determining step—can be identified. 

We now proceed to the main topic of this chapter and examine the situation for an electrochemical reaction that involves multiple consecutive electron-transfer steps of the kind referred to in a general way in the introduction. A hypothetical reaction sequence involving n consecutive electron-transfer reduction steps is given in Scheme 1. The A,s are stable species that can be reactants or products and the ks are reaction intermediates of lower stability. The ZjS indicate the number of electrons trans-... 

In this chapter, transfer coefficients have been developed (hat describe a number of mechanistic possibilities (Section V). The stoichiometric number of a reaction emerges as an important parameter that may be determined by a number of methods. The only reason an electrochemical reaction pathway would show v values > 1 would be to satisfy the material balance for either a reductive (or chemical) dissociation step occurring before a rds as per Scheme 2 or a reductive (or chanical) combination step occurring after a rds as per Scheme 3 (recall that in these schanes reaction steps are written as a series of consecutive reductions, among which may be a chemical step). By considering the types of reaction steps that can give rise to v > 1 within a generalized scheme, an important restriction has... 

To begin with, the basic concepts and definitions related to the model of stepwise processes are introduced and rigorously formulated. This model presumes a series of consecutive one-electron electrochemical reactions with conjugated chemical intervalence reactions, every low valence intermediates taking part in these reactions. The properties of a particular system, including the possibility to observe the separate steps, follow logically from the stability of the intermediates that can be characterised by either equilibrium or rate constants of the intervalence reactions. 

Lev and coworkers [35] developed a radial-flow electrochemical cell coupled to an electrospray interface to study electrochemical reactions involving parallel and consecutive chemical reactions (Figure 5.6). The electrochemical flow cell consists of two cylindrical Delrin blocks (1 and 2) separated by a 50 im Teflon spacer (3). A... 

Generally, the electrochemical reaction is a heterogeneous, multi-step process. These steps can be consecutive or parallel they can include homogeneous chemical reactions, transport processes, adsorption phenomena, crystals nucleation and growing, as well as formation of new phases, etc. However, one essential step, always required to occur in the electrochemical reaction is the electron transfer through the electrolyte solution-electrode phase boundary. Thus, the electronic conductivity of at least one phase is crucial for the reaction to proceed. The overall reaction can involve several electrons the electrons being transferred simultaneously or stepwise. In the latter case, other steps sometimes take place between the electron transfer steps. 

Electrochemical reaction of active chlorine in consecutive reactions at the anode [24]... 

In aqueous solutions, the EC mechanism proposed by Ruiz [13] for the oxidation of AA at low pH is widely accepted. It involves two consecutive one-electron transfer processes to form dehydroascorbic acid immediately followed by irreversible hydration to give the final product 2-3 diketogluco-nic acid. Although the electrochemical reaction is reversible at Hg electrodes [13], the large overpotential needed at carbon electrodes renders the oxidation of AA to be irreversible and the anodic potential (--300 mV at pH 3.9) is considerably higher than its standard value [14, 27], Figure 1. 

A further interesting example from the fundamental point of view is the reaction of quinones, since simple quinones such as benzoquinone and duroquinones are reversible redox systems. Vetter has systematically analyzed the electrochemical reactions of quinones at Pt electrodes and postulated that two electrons are transferred in two consecutive steps [70]. Moreover, photochemical investigations with duroquinone have shown that an intermediate semiquinone exists [71]. Since the exchange currents at a Pt electrode were found to be relatively large [70], the difference in the two formal potentials is expected to be much smaller than that for... 

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