Selective CO Sensing on Single-Atom W@C3N Driven by Double-Channel Orbital Coupling

Selective detection of carbon monoxide (CO) in mixed reducing gas environments remains challenging because chemically similar molecules often produce comparable sensing responses. Here, by combining density functional theory (DFT) and nonequilibrium Green’s function (NEGF) calculations, we identify W@C3N as a single-atom sensing platform with a preferential response toward CO among reducing gases within a series of metal-decorated C3N systems. W@C3N exhibits the strongest CO adsorption and the largest charge transfer, while the adsorbed structure remains dynamically and thermally stable. Electronic structure analysis shows that the CO selectivity originates from double-channel orbital coupling at the W site. Beyond the conventional interaction involving the W dz2 orbital, a reconstructed multi-d-orbital state provides an additional coupling channel near the Fermi level, leading to pronounced interfacial charge redistribution. As a result, CO induces much stronger orbital hybridization and transport modulation than NH3, PH3, and H2S. Especially, the calculated sensitivity toward CO reaches about 10 in a graphene/W@C3N/graphene device model. Our findings reveal that orbital regulation of single-atom centers is an effective route to enhancing CO selectivity within reducing gas environments.