Analysis of Rate Time Constants During Galvanostatic Transients

3 ANALYSIS OF RATE TIME CONSTANTS DURING GALVANOSTATIC TRANSIENTS 

This observation immediately rules out the possibility that NEMCA is an electrocatalytic phenomenon causing only a local acceleration of the catalytic rate at the three-phase-boundaries (tpb) metal-solid electrolyte-gas. In such a case the rate increase would obviously be instantaneous during a galvanostatic transient. 

It was quickly observed that the catalytic rate response during galvanostatic transients can be reasonably well approximated by the response of a first order system, i.e. by  

The physical meaning of the parameter 2FNG/I is obvious It expresses the time required to form a monolayer of oxide ions on a surface with NG adsorption sites when the oxide ions are supplied at a rate I/2F. This proves that NEMCA is a surface phenomenon (not a bulk phenomenon and not a phenomenon at the tpb) taking place over the entire gas-exposed catalyst electrode surface. 

It also shows that electrochemical promotion is due to electrochemically controlled migration (backspillover) of ions (acting as promoters) from the solid electrolyte to the gas-exposed catalytically active catalyst-electrode surface. 

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