Tuning the ORR on graphene-MN₄ single-atom sites via 2D TMD coupling

Transition-metal single-atom sites have emerged as highly efficient oxygen reduction reaction (ORR) electrocatalysts owing to their maximized atom utilization and tunable electronic structures, while two-dimensional transition-metal chalcogenides (RX₂) provide an effective platform for interfacial electronic modulation. In this work, density functional theory calculations are used to investigate the structural stability, electronic properties, and ORR activity of MN₄ centers (M = Fe, Co, Mn) supported on RX₂ substrates (R = Mo, W; X = S, Se, Te). Substrate coupling induces net electron transfer from the MN₄ centers to the RX₂ support, reorganizing the 3d states and modulating both the d-band center and work function. To compare different slab models, the absolute d-band center is introduced as a unified descriptor, which strongly correlates with metal-site electron transfer and the binding strength of key intermediates (O* and OH*). This descriptor quantifies the extent to which substrate coupling weakens the adsorption of ORR intermediates and thereby serves as a useful indicator of the resulting change in ORR overpotential. These results establish a clear connection between interfacial charge transfer and the adsorption of reaction intermediates, providing a practical guideline for the rational design of 2D-material-supported single-atom catalysts.