Why the microkinetic modeling of experimental tafel plots requires knowledge of the reaction intermediate's binding energy

Knowledge of the relation between electrocatalytic activity and the rate‐determining step or the surface coverage of reaction intermediates is crucial to design next‐generation electrocatalysts that may contribute to the sustainability of our society. Commonly, microkinetic models making use of the quasi‐equilibrium or steady‐state assumptions are applied to correlate potential mechanistic descriptions to experimental data, which are usually depicted in the form of a Tafel plot. Yet, there is a discrepancy in the literature on the utility of the quasi‐equilibrium and steady‐state conditions, both of which are approximations per se . This inconsistency is the starting point of the present work, which compares the quasi‐equilibrium and steady‐state approaches for the analysis of a Tafel plot by the concept of free‐energy diagram for a two‐electron process. A correlation between the two frameworks is deduced and important guidelines for the application of the quasi‐equilibrium and steady‐state assumptions are obtained. While the quasi‐equilibrium approach is a suitable approximation for the analysis of a linear Tafel line without change in the Tafel slope, it may fail in the evaluation of a Tafel plot with two linear Tafel regimes. There, the binding energy of the reaction intermediate governs whether the quasi‐equilibrium model is justified, or the steady‐state approach is needed. This implies that density functional theory calculations are indispensably required as a supplement to analyze a Tafel plot with two different Tafel slopes, a situation that is particularly observed for highly active electrocatalysts.