Orbital-level insights into multifunctional electrocatalysis of transition-metal single atoms anchored on WS ₂ monolayers

A comprehensive understanding of single-atom catalysts (SACs) from an orbital-level perspective will provide a simple and direct method for the selection of SACs. Here, using first-principles calculations, we reveal the orbital-level origins of catalytic activity with WS₂-supported transition-metal single atoms (TM@WS₂, TM = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) using the hydrogen evolution reaction (HER), oxygen reduction (ORR) and oxygen evolution (OER) as examples. We show that, for the HER, the activity is primarily determined by the orbital hybridization characteristics and the covalency between the TM atom and adsorbed hydrogen. In contrast, the activities are governed by orbital-specific spin-polarized occupation of antibonding states, which modulates TM-OH bond strength and intermediate adsorption. Among the catalysts, Fe@WS₂, Co@WS₂, Ru@WS₂, and Pt@WS₂ exhibit excellent HER performance, with Fe@WS₂ and Ru@WS₂ achieving particularly low energy barriers <i>via</i> the Volmer-Tafel pathway. Ni@WS₂ exhibits outstanding OER activity, Pd@WS₂ serves as a bifunctional catalyst for the ORR/OER, and Pt@WS₂ demonstrates remarkable trifunctional activity for overall water splitting and metal-air batteries. These insights provide a fundamental orbital-level understanding of catalytic activity, thereby guiding the development of efficient multifunctional electrocatalysts.