Activity Descriptors of Nonmetal Doped Xene-Based Single-Atom Catalysts for Enhanced NO Electroreduction via Hetero-Xene-Layer Integration

Electrochemical NO reduction reaction (NORR) holds promise for sustainable NH3 synthesis but requires an efficient catalyst. Using first-principles calculations, we propose a strategic framework of 12 nonmetal (B/P)-doped single-atom catalysts (SACs), featuring mono- and homo-/heterobilayer xene-based platforms (graphene (Gr) and silicene (Si)), to explore their feasibility for NORR enhancement. In the SACs with a Gr host, tailored NO* physisorption enables the first protonation step on three B-doped variants with low limiting potentials (UL: −0.35 to −0.08 V), achieving high catalytic efficiency. A similar behavior is observed for P-doped SACs, particularly P@Gr/Si, where a strong covalent bonding between P and a Si-bottom atom (in a Si underlayer) modulates the local geometry and electronics at the P-centered area within the P@Gr top layer, thereby significantly weakening NO* adsorption compared with P@Gr and P@Gr/Gr. The bond strength metric, ipCOHP of B(P)–NO*, emerges as a reliable activity descriptor for Gr-based SACs. All Si-hosted SACs exhibit robust NO* chemisorption. B@Si and B@Si/Gr are identified as potential candidates with low UL (−0.46 V and −0.23 V, respectively). The Gr underlayer subtly regulates the electronic landscape at the Si* neighbor in the B@Si top layer, switching the NO* binding mode from the N-end (B@Si) to side-on and relocating active sites for improved overall NO-to-NH3 conversion. The adsorption energy of OH* (ΔEOH*) can serve as a NORR predictor in Si-based SACs, reflecting their vulnerability to OH* poisoning. These findings can guide the rational design of advanced heterostructure SACs for diverse catalytic applications.