RATE-CONSTANT FOR ION TRANSFER IN INHOMOGENEOUS-MEDIA AT THE INTERFACE OF IMMISCIBLE ELECTROLYTES

An expression for the impedance due to ion transfer across the interfa ce of immiscible electrolyte solutions (ITIES) is derived, assuming a continuous change of the ionic resolvation energy across an interfacia l layer. The model is analogous to the Goldman constant field approxim ation. The result is practically identical to the one obtained assumin g an activated step occurs during the transfer, i.e., the classical Bu tler-Volmer relationship, so that the standard rate constant k(0) in t he Butler-Volmer theory is replaced by the quantity D/delta, where D i s the average diffusion coefficient of the transferring ion inside the interfacial layer and delta is the thickness of the interfacial layer . At potentials close to the standard transfer potential, the apparent charge-transfer coefficient alpha takes the value of 1/2. Combination of the charge-transfer impedance and an inner layer capacitance in pa rallel gives a complete semicircle in an impedance plot, characteristi c of a parrallel RC circiut.