Frontier-orbital modulation of rhodium single-atom catalysts for enhanced hydrogen evolution

Abstract Single-atom catalysts (SACs) are promising for hydrogen evolution due to their maximal atomic utilization and discrete energy levels. Modulating metal-support interactions is key to tailoring their activity and stability, yet achieving precise control and mechanistic insight remains challenging and controversial. Here, we construct a rhodium single-atom catalyst model system, with Rh atoms anchored on a series of MoS x Se 2-x supports (Rh SA -MoS x Se 2-x , 0 ≤ x ≤ 2), enabling gradient modulation of metal-support frontier orbital interactions through systematic tuning the anion composition. The elevated lowest unoccupied molecular orbital (LUMO) of MoS x Se 2-x support narrows the energy gap with the highest occupied molecular orbital (HOMO) of Rh atoms, strengthening metal-support orbital hybridization to enhance stability and further amending the LUMO of Rh atoms to optimize both the hydroxide and hydrogen adsorption for high activity. The apex Rh SA -MoSSe catalyst, with optimal HOMO-LUMO hybridization, achieves favorable hydrogen evolution reaction activity and stability simultaneously. This work offers fundamental insights into the metal-support frontier orbital interaction in SACs and establishes a rational design framework for high activity and stability electrocatalysis.