Corrosion & Environmental Degradation
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The Reaction Rate
·For a metal electrode in steady state exchange with the electrolyte, oxidation and reduction are in balance and the material is at its electrode potential. 
  Reduction (cathode):  Mn+ + ne -> M ;   Oxidation (anode):  M -> Mn+ + ne
·These two reactions are thermally activated and their rates may be written in terms of Arenhius relationships: 
   Reduction:   RR = R1 exp(- ER/kT) ;        Oxidation:  RO = R2 exp(- EO/kT)

where ER and EO are the activation energies associated with the reactions. As T increases the reaction rates are seen to increase exponentially.
·At any given temperature these steady state reactions have equal rates, viz.:
            RR= RO = ie;     where ie;is the exchange current density.
·If an external potential, η, is applied to the system, these two reaction rates will be changed as work, neη, will now have to be done to move charge against (with) the applied potential. The reaction rates then become: 
           RR = R1 exp(- {ER-neη}/kT) ,  and     RO = R2 exp(- {EO+neη}/kT)
·For the conditions shown, the reduction reaction rate is increased and the oxidation reaction rate is decreased with respect to the zero field case.