Interpreting concentration and activation overpotentials in electrochemical systems: A critical discussion

In electrochemical systems, it is often desirable to separately quantify the effect of mass transferand reaction kinetics on the cell potential. Respective concentration (mass transfer) and activation (reaction kinetics) overpotentials are frequently defined in different ways. In this work,we discuss the implications of these alternative definitions. In particular, we emphasize that thedifferent definitions for activation and concentration overpotential: (i) cannot be chosen independently to additively partition the cell potential, (ii) can lead to significantly different values,and (iii) result in different meanings of the respective overpotentials. If not applied carefully,they can thus easily result in misinterpretations.