On the shifting peak of volcano plots for oxygen reduction and evolution

Large deviations are often observed between DFT-calculated equilibrium potentials and experimental ones. The deviations can be minimised by semiempirical or fully theoretical correction schemes. However, little is known about the impact of those errors on Sabatier-type activity plots, which are used extensively in electrocatalysis. Here, we show that gas-phase errors can induce drastic changes in the activity plots and may even lead to predictions in stark contrast with experimental results. We obtain simple expressions to accurately predict the location of the Sabatier maxima and the corresponding optimal adsorption energies for a variety of exchange-correlation functionals, using as case studies two important and extensively studied reactions, namely O2 reduction and evolution. The effects are qualitatively and quantitatively different for oxygen reduction compared to oxygen evolution, and the latter is more likely to provide results in qualitative agreement with experiments. In general, and not just for O2 electrocatalysis, accurate gas-phase energetics should become an essential ingredient of volcano plots.