Understanding Free-Energy Landscapes in Electrocatalysis: A Case Study on Nitrate Reduction over Au(111)

• Published in: ACS electrochemistry Vol. 1; no. 6; pp. 910 - 920
• Main Authors: Tayyebi, Ebrahim, Exner, Kai S.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 05.06.2025
• Subjects: nitrate reduction reaction; gas-phase error; atomization energy; free-energy landscape; density functional theory
• ISSN: 2997-0571; 2997-0571
• DOI: 10.1021/acselectrochem.4c00210

Free-energy landscapes are essential tools in electrocatalysis for assessing catalyst activity and selectivity of proton-coupled electron transfer steps. It is a common approach to focus on the thermodynamic part of the free-energy landscape and refer only to the reaction intermediates, which in turn leads to the results being highly dependent on the accuracy of the calculated binding energies of the adsorbed intermediates. Since the evaluation of electrocatalytic processes on solid surfaces usually requires density functional theory calculations (DFT) with periodic boundary conditions, the free energy of the reference molecules relevant for the binding-energy determination is subject to an inherent error. For this purpose, gas-phase error corrections have been introduced in recent years, which allow for a correction of the DFT error, based on the assessment of formation enthalpies, by assigning the error to double or triple bonds of reference molecules. In this contribution, we present a simple approach for an unbiased correction of DFT gas-phase errors: we do not distinguish between the bond order of reference molecules but correct the DFT energies of all molecules with single, double, or triple bonds by referring to atomization free energies of all compounds. We employ our approach to the nitrate reduction reaction on Au(111) as a case study, using different levels of theory with reference to exchange–correlation functionals in the generalized gradient and meta-generalized gradient approximation. It is shown that the inclusion of gas-phase error as well as solvation and ion corrections significantly affects the energetics of free-energy landscapes and activity predictions using descriptor-based analysis, highlighting the importance of correcting DFT-based free energies for gaining reliable insights into electrocatalytic systems.