Towards Understanding the Electrochemical Irreversibility: Origin and Interpretation in Voltammetric Studies

The concept of electrochemical irreversibility originates from the early development of voltammetry, when researchers sought to classify electrode processes according to the speed of the heterogeneous electron transfer. In its strictest sense, irreversibility refers to sluggish electron transfer kinetics, or this is the energetic barrier arising when the standard rate constant ks is small relative to the characteristic timescale of the voltammetric perturbation. Under such conditions, the current–potential response deviates from the Nernstian equilibrium shape, peak-to-peak separation becomes large, and the backward peak is diminished or absent. This purely kinetic interpretation is formalized within Butler–Volmer and Marcus frameworks, where activation barriers for electron transfer are high.
Yet in practice, many aqueous redox couples that might be expected to behave reversibly show apparent irreversibility. In this short contribution, we explain the most important factors that are origin of irreversibility under voltammetric conditions.