Modeling Hydrogen and Oxygen Evolution Reactions on Single Atom Catalysts with Density Functional Theory: Role of the Functional

The most widely used approach to predict catalytic activity is density functional theory, whose results however depend on the adopted exchange-correlation functional. In this work, the role played by the functional in predicting the activity of single atom catalysts (SAC) in the hydrogen and oxygen evolution reactions (HER and OER) is studied. 16 transition metal (TM) atoms embedded in N-doped graphene are simulated and the performance of the widely adopted Perdew-Burke-Ernzerhof (PBE) functional against the hybrid PBE0 functional is assessed. The PBE+U approach, a computationally less complex way to correct for the self-interaction error in density functional theory, is also considered. The predictions obtained with PBE have a substantial deviation from PBE0 for first row TMs, i.e., 3d systems, while smaller deviations are found for the 4d and 5d series. The PBE+U results represent an improvement with respect to PBE, although some differences from PBE0 remain. This study underlines the importance of the choice of the DFT functional in screening new catalysts and in predicting catalytic activities. The use of PBE appears acceptable for 4d and 5d metals, while in the case of 3d systems PBE+U or PBE0 approaches are recommended, in particular for magnetic ground states.