Causal Relationship between Electrochemical Symmetry and Thermodynamic Overpotential

In general, not knowing the origin of a correlation restricts its applicability and prevents safe extrapolations. In particular, there are countless correlations in electrocatalysis nowadays, but their use is limited because the theory behind them is often unclear or nonexistent. This certainly encourages the search for the physics and chemistry beneath correlations. Here, on the example of the oxygen evolution reaction (OER), I show that there is a causal relationship between the thermodynamic overpotential (η_OER), a paramount concept in contemporary computational electrochemistry, and an energetic descriptor called electrochemical-step symmetry index (ESSI). Finally, I use an adsorption-energy database to illustrate the match between the parameters of the relationship predicted by theory and statistical analysis.