A Mean-Field Model for Oxygen Reduction Electrocatalytic Activity on High-Entropy Alloys

High-entropy alloys (HEAs) represent near-equimolar points in the middle of a vast composition space of multi-metallic catalysts. Successful modeling of the catalytic activity of these complex materials allows to search this composition space for optimal catalysts. Previous models of HEA catalytic activity have been based on local and intricate descriptions of the atomic environment on the catalyst surface to predict accurate adsorption energies. These are subsequently used to model the catalytic activity. In this study, we show that by approximating the ligand effect of the surrounding atoms around an adsorption site with a mean-field perturbation corresponding to equimolar AgIrPdPtRu, the same trend in the predictions of the oxygen reduction reaction catalytic activities are obtained for a majority of the quinary Ag-Ir-Pd-Pt-Ru composition space. By comparing to models that consider the ligand effect locally, we show that the extent of such a mean-field approximation is valid up to and including equimolar ternary alloys, corresponding to 60.3 % of the quinary composition space. When extrapolating to make predictions far from near-equimolar compositions, such as for binary alloys, the mean field has been sufficiently perturbed to cause large discrepancies compared to the local models. Here, the intricate models thus prove more useful for discovering optimal catalysts.