Characteristic Decomposition Products Research Articles

Theoretical and experimental study on gas sensing properties of SnO2-graphene sensor for SF6 decomposition products

Based on theoretical calculation and experimental detection, SnO2-modified graphene (SnO2-graphene) was proposed as a gas-sensing material for the SF6 characteristic decomposition products (SO2, H2S, SOF2, SO2F2) in SF6-insulated equipment. Based on density functional theory calculations, the most stable modifying structure of single and double SnO2 on the surface of graphene is optimized. The adsorption structure, adsorption energy, and charge transfer of four gas molecules on the surface of SnO2-graphene are calculated and analyzed. Then the total density of states (DOS) and partial density of states (PDOS) of the system before and after gas adsorption were compared and analyzed to explore the interaction mechanism between different gases and SnO2-graphene. In experimental study, graphene was prepared by the modified Hummers oxidation–reduction method in the laboratory. four concentration gradients of SnO2 modified on the surface of graphene, and then specific gas sensing experiments were carried out with 10, 25, 50, 100 ppm of the SF6 characteristic decomposition products. The gap between simulation and experiment is compared and analyzed, which lays a theoretical and experimental foundation for the development of new specific sensors.

Characterization of partial discharge decomposition of SF6/N2 gas mixture with different microwater contents

The SF6/N2 gas mixture as a preliminary alternative to SF6 is used in the power industry gas insulation medium. At present, the application of the 30% SF6/70% N2 gas mixture has made some progress, but the influence law of microwater content on its discharge decomposition characteristics is still unclear. In this paper, we simulate the defects of metal protrusions in the equipment through needle-plate electrodes, carry out SF6/N2 96hPD and its decomposition characteristic test under different microwater contents, and find that the increase of the microwater content in the SF6/N2 gas mixture will exacerbate the phenomenon of PD, resulting in the enhancement of the average discharge, and under the action of prolonged PD, more characteristic decomposition products will be generated, of which the SOF2 content is the highest, which can be as one of the characteristic components for fault severity judgment. This study provides a certain reference for the specific requirements of the microwater content of the SF6/N2 gas mixture in power equipment.

Adsorption properties of nCu2O-graphene (n = 1, 2, 3) for SOF2 and SO2F2 gas molecules

This study analyzed the adsorption and gas-sensing properties of nCu2O-graphene (n = 1, 2, 3) to SF6 characteristic decomposition products (SOF2 and SO2F2) based on the first-principles calculations. The interaction between the modified graphene monolayer and SOF2 or SO2F2 gas molecules was explored by analyzing adsorption structure, energy, distance, charge transfer, DOS, PDOS, and band gap. The results showed that Cu2O modification improved the conductivity and surface activity of the graphene substrate, and the gas sensitivity of nCu2O-graphene to SOF2 and SO2F2 enhanced. Except for the 2SO2F2/3Cu2O-graphene system, the conductivity of the other system decreased to different degrees. In contrast, the adsorption performance to SOF2 improved more, and the conductivity after the adsorption of SOF2 changed more obviously. Moreover, calculations showed that the recovery time of the SO2F2/Cu2O-graphene system is too short to build stable adsorption. Thus, Cu2O-graphene modified system was not suitable for SO2F2 gas detection. The other gas adoption systems can easily realize adsorption and desorption under suitable conditions. The study results provide a potential material for developing gas sensors using in Gas-insulated switchgear.

Investigating the Electrolyte Degradation of Lithium-Ion Cells with Silicon-Containing Anodes

Silicon with a high gravimetric capacity of 3579 mAh g-1 of the pure material becomes increasingly common in the anode of lithium-ion batteries to increase energy density on the full cell level. However, silicon changes its volume excessively during (de-)lithiation making it prone to ageing. In commercial cells, it is typically applied as SiOx in small quantities in a composite anode together with graphite.Gas analytical studies of Gr/SiOx||NMC622 cells with varying silicon content and carbonate-based electrolyte are presented. The electrolyte consists of 1M LiPF6 in EC:DEC (1:1, v/v) + 5 wt-% FEC. The focus of this study is on investigations of ageing processes such as electrolyte decomposition during formation cycling. All measurements were carried out using specially developed multifunctional test setups and accordingly modified test cells. The different cell specifications were examined by operando mass spectrometry (MS) and post-mortem gas chromatography-mass spectrometry (GC-MS).Strong gas formation leads to a loss of electrolyte, which can cause the cell to dry out and consequently limit the cycle life. Gas analysis is a suitable method to identify decomposition products as well as to illustrate degradation reactions. Operando MS can be used to detect gaseous substances produced by (electro)chemical processes as a function of the state of charge. Furthermore, a post-mortem GC-MS analysis was performed to identify the individual substances qualitatively.The cyclic formation of several degradation products can be determined. Among others, carbon dioxide, hydrogen as well as ethane are identified as characteristic decomposition products of the electrolyte. In addition, the decomposition path of the conducting salt can be detected. Another main result is the evidence of the presence of silicon-containing gaseous fragments as a function of the Si-content in the composite anode.These gas analytical studies of silicon graphite composite anodes provide an important contribution to the understanding of the degradation reactions taking place. The results shown help to illustrate them and give information about the influence of the silicon content on electrolyte degradation. Figure 1

Adsorption of a MoSe2-Based Sensor for Fluorocarbon Gas Decomposition Products in Gas-Insulated Switchgear: A First Principles Analysis

Gas-insulated switch cabinets play a significant role in the power industry, and eco-friendly switch cabinets are the hotspot of current development. With the research of alternative gases for SF6, fluorocarbon insulating gases possessing stable physicochemical properties provide a new insight for scientists. This work studies the sensing and adsorption properties of the Pt–MoSe2 monolayer for fluorocarbon gas characteristic decomposition products of COF2, CF4, and C2F6 in terms of stability, adsorption energy (Ead), charge transfer (QT), band structure (BS), and density of states (DOS) as well as electronic structure based on first principles. The simulation results described Pt as an electron donor in the doping process on the MoSe2 monolayer with a binding force (Eb) of −3.739 eV. The Ead values of the COF2, CF4, and C2F6 gas systems are −0.689, −0.176, and −0.266 eV, respectively. By comparing the BS and DOS of the adsorption system before and after, gas systems become more active, especially the COF2 system. Besides, gas molecules all play the role of an electron acceptor in the adsorption process and the QT of the COF2 system is up to −0.259e. According to the analysis of this paper, Pt-doping can improve the sensing and adsorption properties of the MoSe2 monolayer and the monolayer shows different adsorption phenomena for three gases. The monolayer has a better adsorption effect on COF2, which provides a strong basis for the selective detection of gas sensors.

Investigating the Gas-sensitive Response of Graphene doped by Different TiO2 Concentrations towards SF6 Decomposition Products

SF6 gas will decompose four characteristic decomposition products (H2S, SO2, SO2F2 and SOF2) when an insulation failure occurs early in SF6 gas-insulated equipment. By building gas-sensitive sensors into insulation devices it is possible to detect the characteristic gases of insulation faults. In this paper, we use Graphene which is available with good gas sensitivity, as a substrate and then improve the gas response of Graphene by doping with TiO2 clusters. The adsorption mechanism of (TiO2)n-Graphene (n = 1–4) on four characteristic decomposition gases is firstly analyzed based on first principles, and then verifies experimentally. (TiO2)n-Graphene (n = 1–4) shows the largest change in Eg after adsorption of SO2 gas with 61.70%, 1.07%, 23.19% and 64.04%, respectively. The SEM characterization shows that Graphene has an obvious lamellar structure, and TiO2 nanoparticles are mainly distributed on the outer wall of Graphene, which has a large curvature and strong surface activity. The gas-sensitive response values of the (TiO2)n-Graphene (n = 1–4) sensor for different gases at the same gas concentration are ranked as SO2 > H2S > SO2F2 > SOF2. The results show that TiO2 cluster-doped Graphene is a potential gas-sensitive sensing material that can be a new material for online monitoring of faulty gas content in SF6 gas-insulated equipment.

The calculation of the decomposition products of C5F10O–CO2 mixtures with a chemical kinetic model

This paper presents a chemical kinetic model to investigate the physicochemical process in C5F10O-CO2 mixtures. The model contains 12 ions, including e, C+, O+, C2 +, O2 +, CO+, CO2 +, O−, C−, C2 −, O2 −, O3 − and 38 neutral species, containing C, O, C2, O2, CO, CO2, O3, C5F10O, C4F7Oa, C4F7Ob, C4F7Oc, C4F7Od, C3F5O, C3F4Oa, C3F4Ob, C3F4Oc, C3F4Od, C3F4Oe, C3F3Oa, C3F3Ob, COCF3, C2F2Oa, C2F2Ob, COFC, COF, C3F7a, C3F7b, C3F6a, C3F6b, C2F5, C2F4a, C2F4b, C2F3a, C2F3b, C2F2, CF3, CF2, CF. The total number of 180 reactions are considered. For the reactions whose forward and reverse rate constants can be obtained, the reactions are split into two one-way reactions. In addition, the reactions which produce photons are also considered as one-way reactions. The other reactions are reversable. The reverse rate constants can be obtained by the ratio of the forward rate constants and the equilibrium constants. The molar fractions of the decomposition products in C5F10O-CO2 mixtures with the C5F10O content to be 5%, 7% and 13% are calculated in the temperature range of 500–3500 K. The ratio of the electron temperature to the temperature of the heavy species is calculated to obtain the deviation from local thermodynamic equilibrium in different temperatures. The characteristic decomposition products in different temperature ranges are determined. In addition, the main reaction pathways for the main species are determined by analyzing the contributions of the corresponding reactions to the generation and consumption of the species. In order to validate the chemical kinetic model, the molar fractions of the species in pure CO2 are compared with those by Gibbs free energy minimization in a wide temperature range. This model can help better understand the physicochemical process from the aspect of the reactions during the over-heat fault, and the characteristic decomposition products in different temperature range can help identify the potential fault to avoid great power accidents.

A DFT study on the adsorption properties of Ti3C2O2 MXene towards SF6 decomposition gases

Detecting the partial discharge in gas-insulated switchgear (GIS) equipment by detecting the type and concentration of SF6 characteristic decomposition products is very important and effective in ensuring the regular operation of GIS equipment. In this study, VTi-Ti3C2O2 (Ti-deficient Ti3C2O2) and TM-doped (TM = Ti, Pt, Au) α-type Ti3C2O2 were carried out as the gas-sensing materials. The gas adsorption structures of SO2, SOF2, and SO2F2 on the surfaces of TM-modified Ti3C2O2 were established. Different adsorption systems' adsorption energies, electron densities, state densities, and times for gas desorption were examined using DFT calculations. Following the analysis, physical adsorption of SO2, SOF2, and SO2F2 occurs on the surface of Pt-Ti3C2O2 and Au-Ti3C2O2, while chemical adsorption occurs on the surface of VTi-Ti3C2O2. As a result, it is challenging to remove the gas molecules from the surface of VTi-Ti3C2O2, while it is simple to remove them from Pt-Ti3C2O2 and Au-Ti3C2O2 surfaces. At the same time, compared with gas adsorption on the surface of pristine Ti3C2O2, TM-modified Ti3C2O2 can improve the adsorption performance of pristine Ti3C2O2 on the characteristic decomposition products of SF6 to a certain extent.

Effective pretreatment for thermally-assisted hydrolysis and methylation GC-MS of intractably cross-linked acrylate copolymers

Thermally-assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) using tetramethylammonium hydroxide (TMAH) is an effective approach for the characterization of condensation polymers with ester linkages such as ultraviolet (UV)-cured acrylate resins. However, for intractably cured acrylic resins, reliable structural characterization is often difficult by conventional THM-GC-MS owing to insufficient THM reactions. In this study, a pretreatment to effectively improve THM efficiency was proposed, in which the resin sample was preliminarily soaked and dissolved in a TMAH-methanol solution in a microtube. An aliquot of the TMAH solution was then introduced into the pyrolyzer at 400 °C to produce THM-GC-MS. The effectiveness of the proposed pretreatment was demonstrated using a UV-cured acrylate copolymer consisting of bulky and high-molecular weight bifunctional acrylate (9,9-Bis[4-(2-acryloyloxy ethoxy) phenyl]fluorene) and monofunctional acylate (2-(9 H-Carbazol-9-yl)ethyl acrylate) monomers, for which THM reactions did not proceed efficiently in conventional THM-GC-MS. Conversely, by the modified THM-GC-MS process with a pretreatment involving immersion at room temperature for 24 h or at 60 °C for 30 min, the characteristic decomposition products for each monomer unit were clearly observed in the chromatograms, and the copolymer composition could be precisely estimated from the relative yields of the observed decomposition products. In addition, a methyl acrylate peak, formed from unreacted acrylate moieties in the photocured copolymer, appeared in the chromatogram. Its relative yields were correlated to the double bond conversion in the cured sample. The observed results were successfully interpreted to clarify the curing process of the photocured acrylate copolymer samples.

Mechanistic and Kinetic Investigations on Decomposition of Trifluoromethanesulfonyl Fluoride in the Presence of Water Vapor and Electric Field

As a potential insulation gas to replace sulfur hexafluoride (SF6) due to environmental concerns, trifluoromethanesulonyl fluoride (CF3SO2F) has attracted great interests in various high-voltage electric applications. Thermal stability of CF3SO2F plays an important role in the rational design of the gas-insulated electric equipment. Unimolecular decomposition of CF3SO2F was investigated using high-level ab initio methods including the explicitly correlated RCCSD(T)-F12, the composite ROCBS-QB3, and the multireference RS2 extrapolated to complete basis set limit on the basis of M06-2X-, B2PLYPD3-, and CCSD-optimized geometrical parameters. Rate coefficients and decomposition temperatures were simulated using master equations. CF3SO2F decomposes predominantly via a simple C-S bond cleavage to form CF3 and SO2F, accompanied by a roaming induced F-abstraction detour to release CF4 and SO2, or isomerizes via CF3 migration to the more stable CF3OSFO followed by the production of CF2O and SOF2. Various characteristic decomposition products (e.g., CF4, C2F6, CF2O, SO2, SOF2, SO2F2, CF3H, and so on.) have been identified theoretically through secondary reactions and hydrolysis of CF3SO2F in the presence of water vapor. Electronic structures and stability of CF3SO2F could be affected significantly by the external electric field orientated along the S-C bond. The field-dependent electron-molecule capture rates support that CF3SO2F is superior to SF6 in dielectric strength. The present computational findings shed light on the practical use of CF3SO2F as the replacement gas for SF6.

Adsorption behavior of transition metal (Pd, Pt, Ag and Au) doped SnS monolayers on SF6 decomposed species and the effects of applied electric field and biaxial strain

The adsorption behavior of SF6 characteristic decomposition products (SO2 and SOF2) on intrinsic and transition metal (TM) atom modified SnS monolayers is investigated based on the first principles. The adsorption structure, adsorption energy, density of states, electron localization function, electron density difference, work function, and desorption properties are discussed to evaluate SnS monolayers as potential candidates as adsorbents for SO2 and SOF2. Our results show that the detection performance of the intrinsic SnS monolayer is poor due to the relatively weak interaction with gas molecules. After introducing TM dopants (TM = Pd, Pt, Ag and Au) on SnS monolayer, Pd and Pt atoms tend to be adsorbed on TH sites, while Ag and Au atoms are more easily captured by TS sites. The results of adsorption energy and electronic properties showed that TM atoms could significantly improve the adsorption properties of SO2 and SOF2 molecules on SnS monolayers. Furthermore, the effects of electric field and biaxial strain on the sensing properties of gas molecules on TM-SnS monolayers are also investigated. Finally, the desorption time of gas molecules from the TM-SnS monolayer is estimated to evaluate its potential application in the detection and removal of faulty gases in SF6 power devices. The research results not only reveal the sensing mechanism of the TM-SnS monolayer for the characteristic decomposition products of SF6, but also provide theoretical guidance for the further development of SnS-based adsorbents or scavengers.

Adsorption properties of Ni cluster modified TiO 2 (1 0 1) towards SF 6 decomposition gases

Online detection of insulation defects the decomposition products of SF6 plays a key role in ensuring the safe operation of the gas-insulated switchgear (GIS) equipment. The pristine TiO2 (1 0 1) modified by Ni cluster (1–3 Ni atoms) is used as a new gas-sensing material to study its gas-sensing characteristics to the characteristic decomposition products of SF6: SO2, SOF2, and SO2F2. Through density functional theory (DFT) calculation, we found that the modification of Ni clusters significantly improved the conductivity of pristine TiO2 (1 0 1) and the gas sensitivity of SF6 decomposition products. More importantly, the change of conductivity after gas adsorption lays a theoretical foundation for identifying the type and concentration of SF6 characteristic decomposition products and further judging the type of defects in GIS.

Gas-Sensing Property of TM-MoTe2 Monolayer towards SO2, SOF2, and HF Gases.

Detecting the characteristic decomposition products (SO2, SOF2, and HF) of SF6 is an effective way to diagnose the electric discharge in SF6-insulated equipment. Based on first-principles calculations, Au, Ag, and Cu were chosen as the surface modification transition metal to improve the adsorption and gas-sensing properties of MoTe2 monolayer towards SO2, SOF2, and HF gases. The results show that Au, Ag, and Cu atoms tend to be trapped by TH sites on the MoTe2 monolayer, and the binding strength increases in the order of Ag < Au < Cu. In gas adsorption, the moderate adsorption energy provides the basis that the TM-MoTe2 monolayer can be used as gas-sensing material for SO2, SOF2, and HF. The conductivity of the adsorption system changes significantly. The conductivity decreases upon gases adsorption on TM-MoTe2 monolayer, except the conductivity of Ag-MoTe2 monolayer increases after interacting with SOF2 gas.

Hybrid numerical simulation of the generation and distribution characteristics of SF6 heavy particles under different DC PD energies

To investigate the decomposition law of SF6 under negative direct current partial discharge (PD) at different energies, a SF6 PD hybrid numerical model based on fluid dynamics and plasma chemical reaction models, in which 14 particle species and 24 chemical reactions are considered, is proposed. The effectiveness of the proposed model is validated with the current pulse waveform and the V–I discharge curve obtained by experiment. The influence of discharge energy on SF6 PD characteristic quantities and SF6 decomposition products is investigated with simulation and experiment. The results show that most of the discharge area of SF6 is neutral, and the cation clouds only exist in the ionosphere (4.79–5 mm). With the increase in applied voltage, the electric field intensity of the needle plate gap does not increase completely and even decreases in some areas. Moreover, different from the traditional opinion, the generation of SO2F2 under PD is mainly generated by the hydrolysis reaction of SOF4, which is formed by [SF5], [SF4], and [OH], [O]. The reaction path of [SF2] with O2 is not important. Thus, c(SO2F2)/c(SOF2 + SO2) can be used as the energy characteristic component ratio because of its ability to represent the low-fluorine sulfide ratio n([SF5])/n([SF4]).

Gas Analysis of Ether-Based Electrolytes in Lithium-Oxygen Cells

Low-cost cell chemistries like metal-oxygen batteries are an essential component of future energy storage systems. Due to its very high theoretical energy density the system lithium-oxygen (Li-O2) is an interesting candidate.Gas analytical studies of Li-O2 cells with ether-based electrolytes are presented. The electrolytes used consist of 1M LiTFSI in DEGDME respectively TEGDME. The focus is on investigations of non-linear ageing processes such as electrolyte decomposition during cycling. All measurements were carried out using specially developed multifunctional test setups and accordingly modified test cells. Li-O2 measurements at different O2-flow rates were examined by GC-MS and in-operando MS.Next-generation battery systems typically suffer from severe gassing, which causes a loss of electrolyte and finally the cell to dry out. Consequently, the cycling stability is strongly limited. Gas analysis is a suitable method to identify decomposition and ageing reactions, to benchmark and to define operating parameters. With the GC-MS, a post-mortem analysis could be performed to identify the individual substances qualitatively. In addition, in-operando MS could be used to detect gaseous substances produced by (electro)chemical processes as a function of the state of charge.As major results, the cyclic formation of several degradation products can be demonstrated. CO2, hydrogen as well as methanol, methyl formate, methylal and 1,3-dioxolane were identified as characteristic decomposition products of DEGDME. Furthermore, the presence of many other oxygenated organic compounds can be detected, making it possible to trace the stepwise degradation of DEGDME as a function of the state of charge.These analytical studies make an important contribution to the understanding of the reaction mechanism and ageing reactions in Li-O2 cells with ether-based electrolyte. As a consequence, the shown results help to develop appropriate countermeasures in order to reduce the negative effects mentioned above and thus to ensure a higher cycling stability.This work is funded by the German Federal Ministry of Education and Research (BMBF) in the project “Osaban” (03XP0227B) which is part of the German-Japanese battery cooperation program. The project partners are University of Kyoto (Japan) and Justus-Liebig-University Gießen (Germany). Figure 1

Adsorption and sensing performances of ZnO-g-C3N4 monolayer toward SF6 decomposition products

In this study, ZnO-g-C3N4 monolayer was selected as a gas-sensing material for detecting three characteristic SF6 decomposition products (SO2, SOF2 and SO2F2), based on first-principles theory. The result shows that the electrical conductivity of g-C3N4 system has been remarkably improved after ZnO doping with bind energy of −3.54 eV and Qt of 0.205 e. Each gas molecule can be stably captured on the ZnO-g-C3N4 monolayer by chemisorption, and the electrons are enormously redistributed during the process. The adsorption energy of SO2, SOF2 and SO2F2 after doping are −1.14 eV, −1.61 eV and −1.95 eV, respectively. And compared with the original system, the band gap is reduced by 18.7 %, 89.8 % and 71.9 %, respectively. The recovery time at different temperatures shows that a rapid desorption for SO2 can be achieved by increasing the temperature appropriately, while it is hard to desorb for SOF2 and SO2F2. In conclusion, this study provides a reliable theoretical basis for ZnO-g-C3N4 monolayer as gas sensing material for the detection of SF6 characteristic decomposition products.

Mechanistic Insight into the Decomposition of Eco-Friendly Dielectric Gas Heptafluoro-iso-butyronitrile in the Presence of Water Impurity

Decomposition of heptafluoro-iso-butyronitrile (C3F7CN), a novel eco-friendly dielectric gas for high voltage electrical applications, is investigated theoretically in the presence of water vapor using various computational methods including DFT, CBS-Q, G4, CCSD(T)-F12 and RRKM theory. Hydrolysis of C3F7CN proceeds dominantly via the stepwise addition/isomerization or elimination mechanisms to form amide or HF. The reaction pathways are bifurcated into cis and trans conformations. Activation barriers are strongly dependent on the number of water molecules in hydrolysis due to catalytic effect. The intermediate imidic acid prefers to produce formamido imine via recombination or secondary reaction with C3F7CN. Hydrolysis of CF3 and CF3CFCN undergoes via the direct H-abstraction mechanism to form OH radicals enhancing hydrolysis of C3F7CN. Kinetic calculations predict that imidic acid is the major decomposition product below 500 K while amide is generated exclusively above 1000 K with a small fraction of HF. The present work not only provides a theoretical basis for the increasing risk of dielectric failure of C3F7CN with the increment of the high humidity levels, but also identifies the potential characteristic decomposition products to develop failure diagnostic techniques.

Co, Rh decorated GaNNTs for online monitoring of characteristic decomposition products in oil-immersed transformer

Oil-immersed transformer is one of the most widely used electrical equipment in modern power systems due to its high utilization, safe reliability, and high space utilization. Real-time operation status and insulation fault monitoring of oil-immersed transformer have attracted widespread attention in recent years. In this study, Co, Rh decorated GaN nanotubes is proposed as a novel gas-sensing material for diagnosing the discharge faults in oil-immersed transformer by on-line detecting the characteristic decomposition products. The gas-sensing properties and adsorption mechanism of H2, C2H2 and CH4 on Co, Rh decorated GaNNTs are deeply analyzed from the atomic size. Pristine GaNNTs has circumscribed response to the characteristic decomposition products. While Co, Rh modification can significantly enhance the adsorption capacity of GaNNTs surface, which acts as active sites for gas adsorption due to its virtue of eminent electropositive and catalytic oxidation. Both Co and Rh decorated GaNNTs has strong selectivity to C2H2 and H2 molecules, except CH4 molecule, as only a weak physical adsorption acts on CH4. All calculation data in this work can be employed for practical production of Co, Rh decorated GaNNTs gas sensors, ultimately realizing online monitoring of oil-immersed transformer.

Adsorption properties of Ag2O–MoSe2 towards SF6 decomposed products

In this study, the adsorption and gas-sensing properties of Ag2O–MoSe2 to SF6 characteristic decomposition products (H2S, SO2, SOF2 and SO2F2), have been study based on the first-principle calculations. The optimal structures, adsorption energy, band structure, density of states, differential charge density, and molecular orbital theory were used to analyze the adsorption mechanism. Results show that the adsorption capacity of Ag2O–MoSe2 to SF6 characteristic decomposition products is in following order: H2S > SO2>SO2F2>SOF2. All of the gas molecule adsorptions are exothermic, and occur spontaneously. State density analysis shows that H2S and SO2 adsorption belongs to chemical adsorption, while SOF2 and SO2F2 interact by physical adsorption. The recovery time shows that H2S is difficult to desorption after adsorption. While the desorption time of SO2 is much shorter than H2S, which improve the detection efficiency. In addition, the dissociation time of SOF2 and SO2F2 is very short. In conclusion, Ag2O–MoSe2 can be a potential gas sensing material for these four SF6 characteristic decomposition products detection.

The Adsorption and Sensing Performances of Ir-modified MoS2 Monolayer toward SF6 Decomposition Products: A DFT Study.

In this paper, the Ir-modified MoS2 monolayer is suggested as a novel gas sensor alternative for detecting the characteristic decomposition products of SF6, including H2S, SO2, and SOF2. The corresponding adsorption properties and sensing behaviors were systematically studied using the density functional theory (DFT) method. The theoretical calculation indicates that Ir modification can enhance the surface activity and improve the conductivity of the intrinsic MoS2. The physical structure formation, the density of states (DOS), deformation charge density (DCD), molecular orbital theory analysis, and work function (WF) were used to reveal the gas adsorption and sensing mechanism. These analyses demonstrated that the Ir-modified MoS2 monolayer used as sensing material displays high sensitivity to the target gases, especially for H2S gas. The gas sensitivity order and the recovery time of the sensing material to decomposition products were reasonably predicted. This contribution indicates the theoretical possibility of developing Ir-modified MoS2 as a gas sensor to detect characteristic decomposition gases of SF6.