Reverse reaction cathodic

It is not appropriate here to consider the kinetics of the various electrode reactions, which in the case of the oxygenated NaCl solution will depend upon the potentials of the electrodes, the pH of the solution, activity of chloride ions, etc. The significant points to note are that (a) an anode or cathode can support more than one electrode process and b) the sum of the rates of the partial cathodic reactions must equal the sum of the rates of the partial anodic reactions. Since there are four exchange processes (equations 1.39-1.42) there will be eight partial reactions, but if the reverse reactions are regarded as occurring at an insignificant rate then... 

Strictly speaking I0 is a measure of the electrocatalytic activity of the tpb for a given electrocatalytic reaction. It expresses the rates of the forward (anodic) and reverse (cathodic) electrocatalytic reaction under consideration, e.g. reaction (4.1), when there is no net current crossing the metal-solid electrolyte or, equivalently, the tpb. In this case the rates of the forward and the reverse reactions are obviously equal. It has been recently shown that, in most cases, as one would intuitively expect, I0 is proportional to the length, tpb, of the tpb.8... 

Figure 6.7 shows a typical special feature of the polarization curves. In the case of reversible reactions (curve 1), the anodic and cathodic branches of the curve form a single step or wave. In the case of irreversible reactions, independent, anodic and cathodic, waves develop, each having its own inflection or half-wave point. The differences between the half-wave potentials of the anodic and cathodic waves will be larger the lower the ratio fH. ... 

In a round-trip potential scan the values of corresponding to the anodic and cathodic direction are different. For reversible reactions the difference is minor, according to Eq. (12.9) (i.e., only 0.056/n V regardless of the component concentrations and of the potential scan rate v). It is typical for irreversible reactions that the difference between these potentials is much larger (Fig. 12.9) the gap between the maxima increases with decreasing value of the reaction rate constant and increasing scan rate v. 

Consider the shape of the E vs. t relation for the cathodic reaction Ox + ne — Red, and assume that the initial product concentration = 0. Assume further that the share of nonfaradcaic current is small and that all the applied current can be regarded as faradaic. In reversible reactions the electrode potential is determined by the values of c. and Prior to current flow the potential is highly positive since Ci, red = v,xsi 0- When the current has been turned on, the changes in surface concentrations are determined by Eqs. (11.10). Substituting these values into theNemst equation and taking into account that in our case = 0, we obtain... 

The behavior in the regions of moderate anodic or cathodic polarization depends on the relative positions of potentials E and Eq, which in turn depend on the relative values of constants and k 2- For E which are more positive than Eq (Fig. 13.1a), relation (13.20) for the cathodic CD remains valid at all values of cathodic polarization (except for the region of low values where the reverse reaction must be taken into account). At moderate values of anodic polarization, inequalities (la) and (2b) are found to be valid at potentials more negative than E, while step 2 becomes rate determining, which is the second step along the reaction path. In this case [see Eq. (13.10)], we have... 

Cathodic hydrogen evolution is one of the most common electrochemical reactions. It is the principal reaction in electrolytic hydrogen production, the auxiliary reaction in the production of many substances forming at the anode, such as chlorine, and a side reaction in many cathodic processes, particularly in electrohydrometallurgy. It is of considerable importance in the corrosion of metals. Its special characteristic is the fact that it can proceed in any aqueous solution particular reactants need not be added. The reverse reaction, which is the anodic ionization of molecular hydrogen, is utilized in batteries and fuel cells. 

Note 7 cathode is the standard reduction potential and node is the standard oxidation potential, (iv) No, the standard reaction will not occur as written since i ceii < 0 the reverse reaction will occur. 

The cathode reaction comes directly from a table of standard reduction potentials, while the anode reaction is the reverse reaction from such a table. However, how did we know that it was the fluorine reaction requiring reversal ... 

Physiologic electron acceptors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) produced similar effects on cathodic hydrogen evolution from mild steel as achieved with methyl viologen (Bryant and Laishley 1990). These experimental results showed that the mild steel rods reacting with phosphate can preferential act as electron donors for the reduction of low-potential electron carriers. All hydrogenases catalyze a reversible reaction for the formation and oxidation of hydrogen, which requires low-potential electron carriers for the enzyme activity (Church et al. 1988 Fauque et al. 1988). 

For each cathodic stripping mechanism, the dimensionless net peak current is proportional to the amount of the deposited salt, which is formed in the course of the deposition step. The amount of the salt is affected by the accumulation time, concentration of the reacting ligand, and accumulation potential. The amount of the deposited salt depends sigmoidally on the deposition potential, with a half-wave potential being sensitive to the accumulation time. If the accumulation potential is significantly more positive than the peak potential, the surface concentration of the insoluble salt is independent on the deposition potential. The formation of the salt is controlled by the diffusion of the ligand, thus the net peak current is proportional to the square root of the accumulation time. If reaction (2.204) is electrochemically reversible, the real net peak current depends linearly on the frequency, which is a common feature of all electrode mechanism of an immobilized reactant (Sect. 2.6.1). The net peak potential for a reversible reaction (2.204) is a hnear function of the log(/) with a slope equal to typical theoretical response... 

From experiments on the evolution of hydrogen at various metal cathodes in dilute sulphuric acid, Tafel in 1905 observed that an extra driving force was required to cause electrolysis to proceed at appreciable rates, expressed by the current density j [35]. The overpotential T is the difference between the working electrode potential and the reversible reaction potential and was related to current... 

Let us consider a semiconductor electrode, at which a redox reaction of type (1) occurs. Electrons of both the conduction band and valence band may take part in the electrode process. As a result, the reversible reaction considered is characterized by four different types of electron transitions (see Fig. 6a). Transitions in which electrons leave the semiconductor and holes come in contribute to the cathodic current, and those where electrons come in and holes escape contribute to the anodic current. Thus, the resultant current is a sum of four currents i p, i >p (when referring to currents we shall always mean current densities). 

Figure 17-23a illustrates a reversible reaction that is fast enough to maintain equilibrium concentrations of reactant and product at the electrode surface. The peak anodic and peak cathodic currents have equal magnitudes in a reversible process, and... 

The exchange current density is the electrode reaction rate at the equilibrium potential (identical forward and reverse reaction rates) and depends on the electrode properties and operation. The typical expression for determining the exchange current density is the Arrhenius law (3.23), where the constant A depends on the gas concentration. Costamagna et al. [40] provide the following expressions for the anodic and cathodic exchange current density, respectively ... 

The capillary plasma reactor consists of a Pyrex glass body and mounted electrodes which are not in direct contact with the gas flow in order to eliminate the influence of the cathode and anode region on CO2 decomposition. Analysis of downscaling effects on the plasma chemistry and discharge characteristics showed that the carbon dioxide conversion rate is mainly determined by electron impact dissociation and gas-phase reverse reactions in the capillary microreactor. The extremely high CO2 conversion rate was attributed to an increased current density rather than to surface reactions or an increased electric field. 

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