Exchange reaction current

Determining the cross-exchange reaction current can yield some useful information. For a system under SR kinetic control, mediation takes place in a thin reaction layer adjacent to the film/solution 

Fig. 7-5. Tafel plot of reaction current io = exchange reaction current at equilibrium.

Fig. 9-3. Polarization curves estimated for a simple electrode reaction of metallic ion transfer i = reaction current to - exchange reaction current in reaction equilibrium = symmetric factor (0 < 3 < 1).

Integration of Eqn. 8-18 with respect to electron energy e to produce Eqn. 8-20 yields the exchange reaction current io  

Introducing Eqn. 8-17 into Eqn. 8-20, we obtain Eqn. 8—21 as an approximate equation for the exchange reaction current io  

RBDox), an anodic potential-independent current (dashed line) or a cathodic potential-independent ourent (solid line) equivalent to the exchange reaction current occurs near the equilibrimn redox potential. 

It follows from Eqn. 8-53 that the ratio of participation of the conduction band to the valence band in the exchange reaction current depends on the standard Fermi level of the redox electrons relative to the middle level in the band gap at the interface of semiconductor electrode. 

Fig. 8-39. Electron state density in an electrode metal, Du, a semiconductor film, Dt, hydrated redox particles, Dredox, and exchange reaction current of redox electrons, t., in electron transfer equilibrium M = exchange current at a bare metal electrode, M/F= exchange current at a thin-film-covered metal electrode.

Fig. 8-4. (a) Electron state density D in a metal electrode and in hydrated redox particles, (b) rate constant for electron ttmneling k, and (c) exchange reaction current electron transfer in eqiiilibrium with a redox reaction sl = lower edge of an allowed band of metal electrons. [From Gerischer, I960.] 

Fig. 8-16. Electron state density in a semiconductor electrode and in hjrdrated redox partides, rate constant of electron tunneling, and exchange redox current in equilibrium with a redox electron transfer reaction for which the Fermi level is close to the conduction band edge eF(sc) = Fermi level of intrinsic semiconductor at the flat band potential 1. 0 (tp.o) = exchange reaction current of electrons (holes) (hvp)) - tunneling rate constant of electrons (holes).

In eqxiilibrium of electron transfer, the Fermi level of an electrode equals the Fermi level of the redox particles (eksc) = erredox)) the forward reaction current equals the backward reaction current, which both equal the exchange reaction current to. Further, the exchange current is the sum of the conduction band current, and the valence band current, ip,o (io = in.o + tp,o)- The exchange currents t o and ij, are given, respectively, by Eqns. 8-48 and 8—49  

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