Other non-blocking interfaces

A number of non-blocking interfaces can be formed where neither of the phases is a simple metal. Some examples are  

LiCFjSOa-PEO/Li VgOij (Bruce and Krok, 1988) where the Li ion tends to equilibrate between the phases. 

AsPh4BPh4-PVC/AsPh4Cl-H20 where the AsPh ion equilibrates between the phases. 

There will always be a charge transfer resistance (R i) associated with the ion exchange across the interface. Where there are very small Debye lengths in each phase (compared with the size of an ion) the exchange current I o can be evaluated from the relationship 

In general it will be necessary to measure via impedance measurements using a four electrode cell. A schematic diagram of the cell which would be used for such measurements is shown in Fig. 10.15. The expected behaviour will be as described in Eqn (10.3) except that Warburg impedances can arise from either or both phases. An example of an impedance spectrum of the H2O/PVC interface is shown in Fig. 10.16. The application of a constant overpotential will, in general, lead to a slowly decaying current with time due to the concentration changes which occur in both phases, so that steady state current potential measurements will be of limited use. 

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