Abstract
When theoretical impedance-frequency “data” calculated from an exact small-signal ac solution of the transport equations for an unsupported intrinsic-conduction situation are fitted to an appropriate equivalent circuit using nonlinear complex least squares, one finds that a non-zero apparent charge transfer resistance is necessary for a good fit even when charges of one sign are taken completely blocked at the electrodes and those of opposite sign are taken as completely unblocked. Normally, one would expect no reaction resistance under these conditions. This effect only occurs when positive and negative charges have different mobilities and may be ascribed to ambipolar drag of one set of charges on the other set. Here we demonstrate the effect and derive approximate relations to be used in data analysis which should allow an accurate estimate of the true reaction rate to be obtained when it is not too large. The practical limit to the maximum reaction rate which can be derived from experimental impedance data for the present situation is shown to depend on both a diffusion coefficient and the Debye length.
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