On the current-voltage characteristics of charge transfer reactions at mixed conducting electrodes on solid electrolytes

Even though the electrochemical oxygen reduction reaction at mixed conducting oxide electrodes is highly important for several applications of solid electrolytes a thorough discussion of the kinetics of electron and ion transfer steps at the corresponding electrode surface is not available yet. A straightforward application of current voltage (I-V) relations derived for charge transfer reactions at electrode/electrolyte interfaces turns out to be inappropriate. In this contribution, a model is presented that relates concentrations of electrochemically active species and electrostatic potential steps at the electrode/gas interface of mixed conducting electrodes to the applied overpotential, and thus I-V formulas for the corresponding electron and ion transfer reactions are obtained. Depending on the specific parameters surprising effects are found such as an additional factor of two in the exponents of the I-V relation, irrelevance of the symmetry factor or limiting currents even if charge transfer is rate determining.