Electrode potential in electron transfer equilibrium

The electrode potential defined in Sec. 4.3 applies to both nonpolarizable electrodes at which charge transfer reactions may take place and polarizable electrodes at which no charge transfer takes place. For nonpolarizable electrodes at which the charge transfer is in equilibrium, the interfacial potential is determined by the equilibrium of the charge transfer reaction. 

For an electronic electrode at which the transfer of redox electrons is in equilibrimn (OX i + e(jj) = RED q), as shown in Fig. 4-17, the Fermi level EpdUEDoxs) of redox electrons e(REDox., s in hydrated redox particles equals the Fermi level cp(M) of electrons e,io in the electrode the energy for the electron transfer across the electrode interface is, then, zero (a M/s) = 0). Consequently, the electron level u M/aAo in the electrode equals the electron level a, s/v) in the aqueous solution, i.e. the redox electron level a KEoax s) of hydrated redox particles. 

The electrode potential, E, represented by the real potential x,iwsrr) of electrons in the electrode, then, corresponds to the enei level a BBiwir of redox electrons in the hydrated redox particles in aqueous solution as shown in Fig. 4-18 and defined in Eqn. 4-19  

follows that the electrode potential in electron transfer equilibriiun represents the redox electron level of the redox particles in aqueous electrolyte solution. Further, it follows from Eqn. 4-19 that the electrode potential in the transfer equilibrium of redox electrons is characteristic of individual redox reactions but independent of the nature of the electrode materials. 

The electrode potential in the equilibrium of redox electron transfer may also be defined by the free enthalpy change in the reaction of the hydrated redox particles with the standard gaseous electron eisro) as shown in Eqn. 4—20  

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