Cathodic reduction current

In the first reaction (Eq. 5.47), the reduction of H2O2 and the oxidation of the radical =Ge involves an electron transfer whereas the other (Eq. 5.48) is a pure chemical process. It is clear from this set of reactions that the hydroxide surface is the only stable component in the presence of H2O2. In addition, it explains the occurence of a stationary cathodic reduction current. It should be mentioned here that there are different ways of testing whether a reaction involves electron or hole transfer, a.s will be discussed in detail in Chapter 7. 

The same reactions occur at the corresponding n-type electrode (Fig. 8.12). In the anodic range, the total current remains very small upon addition of the redox system. However, it is determined by two partial currents, namely the cathodic reduction current and the anodic decomposition current, as can be proved analytically. A description in terms of quasi-Fermi levels has already been given in Section 7.4.1. 

The difference is discussed in the succeeding text.) Within the voltage range of 0 to -0.3 V versus SCE only a small residual current flows. It is conventional in polarography to represent cathodic (reduction) currents as positive and anodic (oxidation) currents as negative. The residual current actually comprises two components, a faradaic contribution and a charging or double-layer current contribution ... 

In 1948 Kalousek introduced the commutator method to establish the reversibility of certain inorganic and organic redox processes. In this method, the electrode potential is alternately switched from a potential at which the reduction product is formed to that potential at which it is reoxidized (cf. cyclic voltammetry). The mean current is recorded against the increasing potential and, for a polarographically reversible process, the observed cathodic (reduction) current is equal but opposite to the anodic (oxidation) current. 

At a time t, less than T the cathodic reduction current is replaced with an anodic oxidation current, causing the reoxidation of the R species obtained during reduction. A reverse potential time curve is observed, with a reverse transition time T. For the case in which i = -i, one obtains the relation ... 

In this equation, which may be regarded as the electrochemical equivalent of the well-known Arrhenius expression with two exponential terms representing anodic (oxidation) and cathodic (reduction) currents [74], the current I observed at the electrode, when both A and B are soluble in solution, is related to the electrode area A, the standard rate constant (in m s"0> the surface concentrations [A] =o [ ]x=o>the transfer coefficient a, and the overpotential Further, n denotes the number of electrons transferred per... 

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