Anion-tuned d-p hybridization breaks activity-stability trade-off in single-atom hydrogen evolution catalysts

Single-atom catalysts hold great promise for hydrogen evolution reactions due to their maximal atomic utilization and discrete energy levels. Modulating metal-support interactions is a powerful strategy for tailoring the electronic structure and catalytic performance of single-atom catalysts. However, achieving precise control and gaining mechanistic insight into these interactions, especially at the orbital level, remains challenging and often controversial. Here, we construct a model system of rhodium single-atom catalysts, in which isolated Rh atoms are anchored on a series of molybdenum sulfide selenide supports (Rh _SA -MoS _x Se _2−x , 0 ≤ x ≤ 2), enabling gradient-continuous modulation of metal-support d-p orbital interactions through systematic tuning of the support p-band structure. We demonstrate that the d-band center of Rh single-atoms exhibits a volcano-type relationship with key HER descriptors, such as hydrogen and hydroxide binding energies, where hybridization-induced d-band position optimizes intermediate adsorption/desorption kinetics, and strengthened Rh-S/Se covalent interactions enhance durability. The apex Rh _SA -MoSSe catalyst, with optimal d-p orbital hybridization, achieves superior HER activity and exceptional stability simultaneously. This work offers fundamental insights into the band structure-activity relationships of SACs and establishes a rational design framework for high-efficiency electrocatalysis through support-mediated d-p orbital hybridization.