Overpotentials adverse effects

Two electrode measurements used to determine o o, or o, of a bulk MIEC may suffer from errors due to the electrode overpotential. Methods used for eliminating this adverse effect in electronic conductors or SEs cannot be simply applied to MIECs. The use of a four-probe arrangement requires a detailed analysis of the I-V relations which depend on the defect nature of the MIEC. The result is a nontrivial extension of the two point I-V relations, as the I-V relations may not be linear, but exponential. For the / , n N" defect model... 

It is thus seen that interpretation of Tafel slopes requires information on adsorption behavior as /(F), complementary to that as /(C,). The derivative dln6/d nC, required for interpretation of reaction order, R = dlni/dlnC, must also be taken at a controlled potential that is, d n6/d nC,)y/, the isotherm derivative in the reaction-order expression (Section X), must also be evaluated at constant overpotential, r , or electrode potential, V, in the case of electrocatalytic reactions, especially those involving small organic molecules or Cl. Unfortunately, in many experimental works on electrode kinetics, except those on pH effects, these important details involving the adsorption behavior of reactant and/or intermediate(s) have been neglected, with adverse consequences for mechanism determination. 

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