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When partial discharges occur in air-insulated equipment, the air decomposes to produce a variety of contamination products, resulting in a reduction in the insulation performance of the insulated equipment. By monitoring the concentration of typical decomposition products (CO, NO, and NO 2 ) within the insulated equipment, potential insulation faults can be diagnosed. MoS 2 has shown promising applications as a gas-sensitive semiconductor material, and doping metal oxides can improve the gas-sensitive properties of the material. Therefore, in this work, MoS 2 has been doped using the popular metal oxides (ZnO, TiO 2 ) of the day, and its gas-sensitive properties to the typical decomposition products of air have been analyzed and compared using density functional theory (DFT) calculations. The stability of the doped system was investigated using molecular dynamics methods. The related adsorption mechanism was analyzed by adsorption configuration, energy band structure, density of states (DOS) analysis, total electron density (TED) analysis, and differential charge density (DCD) analysis. Finally, the practical application of related sensing performance is evaluated. The results show that the doping of metal oxide nanoparticles greatly improves the conductivity, gas sensitivity, and adsorption selectivity of MoS 2 monolayer to air decomposition products. The sensing response of ZnO-MoS 2 for CO at room temperature (25 °C) reaches 161.86 with a good recovery time (0.046 s). TiO 2 -MoS 2 sensing response to NO 2 reaches 3.5 × 10 6 at 25 °C with a good recovery time (0.108 s). This study theoretically solves the industrial challenge of recycling sensing materials and provides theoretical value for the application of resistive chemical sensors in air-insulated equipment.

Ti 3 C 2 T x MXene is an emerging two-dimensional transition-metal carbide/nitride with excellent properties of large specific surface and high carrier mobility for room-temperature gas sensing. However, achieving high sensitivity and long-term stability of pristine Ti 3 C 2 T x -based gas sensors remains challenging. SnO 2 is a typical semiconductor metal oxide with high reaction activity and stable chemical properties ideal for a dopant that can comprehensively improve sensing performance. Ti 3 C 2 T x and SnO 2 are investigated for the first time in this study as functional materials for hybridization and room-temperature detection of the gas insulating medium fluorinated nitrile (C 4 F 7 N) with microtoxicity. A Ti 3 C 2 T x -SnO 2 nanocomposite sensor exhibits superior sensitivity, high selectivity, strong anti-interference ability, and excellent long-term stability. The enhanced sensing mechanism is ascribed to the synergistic effect between SnO 2 and Ti 3 C 2 T x and the strong adsorption ability of SnO 2 to C 4 F 7 N similar to bait for fish. We also established an actual leakage scene and demonstrated the feasibility of the Ti 3 C 2 T x -SnO 2 sensor to provide distribution rules with high sensing efficiency for actual engineering applications. The results of this work can expand the gas sensing application of Ti 3 C 2 T x MXene and provide a reference for maintaining C 4 F 7 N-based eco-friendly gas-insulated equipment.

C 4 F 7 N (fluorinated nitrile) has been introduced as a remarkable substitute gas for the greenhouse gas SF 6 (sulfur hexafluoride) which is used in gas-insulated equipment (GIE). Intensive investigations about the compatibility between C 4 F 7 N and materials used in GIE are required to decide their long-term behavior. In this paper, the interaction mechanism between EPDM, used as a sealing ring in GIE, and C 4 F 7 N-CO 2 was explored. The composition and morphology properties of EPDM were first revealed based on scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that EPDM rubber is incompatible with the C 4 F 7 N-CO 2 gas mixture at temperatures higher than 70 °C. There exist chemical reactions between EPDM and C 4 F 7 N, resulting in the generation of gaseous byproducts including C 3 F 6 , CF 3 H, and C 2 F 5 H and corrosion of EPDM. DFT calculation also shows that the interaction between C 4 F 7 N and EPDM could cause the dissociation of C 4 F 7 N. Relevant results provide important guidance for the engineering application of the C 4 F 7 N gas mixture., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

The C 4 F 7 N (fluorinated nitrile) gas mixture has been recognized as the most potential substitute gas to SF 6 used in gas-insulated equipment. In this paper, we explored the thermal stability and decomposition properties of the C 4 F 7 N-N 2 -O 2 gas mixture. The influence mechanism of oxygen content and temperature on the byproduct generation was obtained and analyzed. It was found that thermal decomposition of the C 4 F 7 N-N 2 -O 2 gas mixture mainly produces CO, C 3 F 6 , C 3 F 8 , CF 3 CN, (CN) 2 , and COF 2 . The addition of oxygen could accelerate the decomposition of C 4 F 7 N. The content of C 3 F 6 and (CN) 2 decreases, while the yield of CF 4 , CO, C 3 F 8 , and COF 2 increases with the oxygen content. Thermal decomposition of the C 4 F 7 N-N 2 -O 2 gas mixture at temperatures lower than 425 °C results from the interaction between C 4 F 7 N and the metal heating element, while the bond cleavage reactions occur at higher temperature. As for engineering application, the oxygen added in the 6%C 4 F 7 N-94%N 2 gas mixture should not exceed 6% to avoid the negative effect of oxygen on the thermal stability of C 4 F 7 N., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

We carried out a density functional theory study to investigate the adsorption behavior of four kinds of SF 6 decomposed products over the ZnO(101̅0) surface. The effects of O and Zn vacancies on the surface were also considered. For perfect ZnO(101̅0) surface, the adsorption of SO 2 and H 2 S exhibits stronger chemical interactions compared to the adsorption of SOF 2 and SO 2 F 2 . For SO 2 and H 2 S adsorption, there may exist new chemical bond formation between the molecule and the surface and the H 2 S molecule experiences one H-S broken bond. The introduction of O vacancy cannot obviously enhance the chemical interactions between these four molecules and the surface. However, the Zn vacancy on the surface can significantly elevate the chemical interactions between SO 2 /H 2 S and the surface. The two-coordinated O atom (O 2c ) on the surface plays an important role. For SO 2 and H 2 S adsorption, the S atom in SO 2 or H 2 S tends to bond to the O 2c atom, bringing much larger adsorption energy compared to the adsorption over the perfect ZnO(101̅0) surface. This work can provide a basis for surface modification of ZnO in applications to detecting SF 6 decomposed products by theoretical evaluation., Competing Interests: The authors declare no competing financial interest.