Thermodynamic stability of single-atom catalysts in electrochemical conditions from first principles: Role of the local coordination

Single-Atom Catalysts (SACs) are a hot topic in catalysis research. Nowadays, there is a growing attention in modelling the reactivity and activity of SACs towards several electrochemical reactions. The activity of SACs is strongly sensitive to the local coordination of the transition metal atoms. An aspect less explored is assessing their stability in electrochemical conditions. In this work, we performed a density functional theory investigation of SACs based on MoS2, a widely adopted supporting material, by focusing on the role of the local coordination to the stability. Our results are based on a dataset of fifteen transition metal atoms on four different possible coordinative sites. The stability of SACs in electrochemical conditions is predicted by using a recently proposed simple yet practical scheme within the formalism of Pourbaix diagrams [ACS Catal. 14, 45 (2024)]. When looking at the role of the metal, Pt-SACs are mostly stable, compatible with the large diffusion of these kinds of systems in experiments. Results show that the local coordination has a dramatic effect on stability. Most often the simple adsorption of metals on MoS2 leads to unstable systems, unless noble atoms are considered. Moreover, stability improves when metal atoms occupy lattice S sites, but the most stable configurations refer to substitutional doping of Mo atoms. The results provided are validated against selected available experimental data. These results provide a further example of the crucial role of the local coordination in single-atom catalysis and may of help for the screening of potential candidates and could be used to help the understanding of the active phase in promising electrocatalysts.