Overvoltage - An Electrical Irreversibility

The widely used Tafel plot (Koryta, 1993) of log current density against overpotential yields information about the magnitude of the exchange current. 

The three-phase interface can be favourably influenced by the introduction of a thin layer of material, capable of conducting both ions and electrons, between the electrolyte and the electrode structure. 

For the SOFC, for example, the use of uranium oxide has been studied but not adopted. The onset of current cut-off by concentration polarisation can be delayed, so that the maximum current obtainable is increased, a significant reduction of irreversibility. SOFC cathodes now almost universally use a coating of lithium strontium manganate, a joint electron/ion conductor. 

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