Study on the adsorption behavior, and electronic and gas-sensing properties of SF₆ decomposition products on Co- and Ni-modified g-C₃N₄ monolayer films

This work addresses potential failures in SF₆ gas-insulated equipment, including insulation degradation and device breakdown caused by decomposition products. This work employs first-principles (DFT) calculations to systematically investigate the modulation mechanism by which transition metal (Co, Ni) doping influences the adsorption performance of two-dimensional graphitic carbon nitride (g-C₃N₄) toward SF₆ decomposition gases (H₂S, SO₂, SOF₂, and SO₂F₂). The results demonstrate that transition metal doping significantly alters the electronic structure of g-C₃N₄: Ni doping reduces the bandgap from 1.535 eV to 0.312 eV, whereas Co doping decreases it to 0.828 eV. This electronic structure modulation transforms the material's adsorption behavior from weak physical adsorption to strong chemical adsorption. Specifically, the Ni-g-C₃N₄ system exhibits adsorption energies of -2.251 eV, -1.562 eV, -1.976 eV, and -1.900 eV for SO₂, H₂S, SOF₂, and SO₂F₂, respectively, which are higher than those observed for the Co-g-C₃N₄ system. Differential charge density and frontier orbital analyses indicate that the enhanced adsorption is due to strong interactions between the transition metal 3d orbitals and the polar atoms (S, O, and F) in the gas molecules. Notably, upon H₂S adsorption, the bandgap of the Ni-g-C₃N₄ system further decreases to 0.245 eV, suggesting potential for ultra-high sensitivity detection. These findings offer new insights for the development of high-performance sensors for SF₆ decomposition products: Ni doping is ideally suited for scenarios demanding extreme detection sensitivity, while Co doping may provide advantages in terms of long-term stability. Overall, this study not only deepens the understanding of electronic structure modulation in g-C₃N₄-based gas-sensing materials but also establishes a theoretical foundation for the design of early-warning sensors for SF₆ insulation faults in power systems.