A DFT Investigation of SF6 Decomposition Products’ Adsorption on V-Doped Graphene/MoS2 Heterostructures

The detection of sulfur hexafluoride (SF6) decomposition products is critical for diagnosing insulation faults in gas-insulated switchgear (GIS). In this study, a vanadium-doping strategy was incorporated into the graphene/MoS2 (GM) heterojunction to design a vanadium-doped graphene/MoS2 (GMV) heterojunction material. Leveraging first-principles density functional theory (DFT), the adsorption behaviors of five characteristic SF6 and its decomposition gases (H2S, SO2, SOF2, SO2F2) on intrinsic GM and GMV were systematically investigated to evaluate their potential for gas sensing applications. Computational results reveal that intrinsic GM exhibits only weak physical adsorption toward all target molecules, with low adsorption energies and negligible charge transfer, which fails to meet practical application requirements. In contrast, GMV demonstrates significantly enhanced adsorption energies for H2S, SO2, and SOF2 at vanadium sites (with a maximum value of −0.388 eV for SO2) and shorter adsorption distances, while SO2F2 and SF6 preferentially adsorb near electron-deficient carbon regions. Intrinsic GMV displays semimetallic properties, with a Fermi level at 0.126 eV and a band gap of 0.0017 eV. Upon adsorption of H2S, SOF2, SO2F2, or SF6, the Fermi level undergoes a moderate shift (ranging from −1.083 eV to +0.349 eV), with minimal changes in the band gap. Conversely, SO2 adsorption induces a substantial downward shift of the Fermi level to −1.732 eV, accompanied by the emergence of a sharp partial density of states (PDOS) peak near the Fermi level (0–1.5 eV), indicating strong orbital coupling and significant charge transfer. Furthermore, recovery times calculated using classical formulas show that at room temperature and a frequency of 1 × 106 Hz, the recovery time of GMV for SO2 is 2.43 s, outperforming the other four gases and satisfying practical gas sensing requirements. Through comprehensive analysis of adsorption distances, electronic structure changes, and recovery times, GMV exhibits higher selectivity toward SO2. Thus, GMV can serve as a sensing material for detecting GIS insulation faults associated with elevated SO2 concentrations, offering a viable strategy for advancing online monitoring technologies in power systems.