Investigation of Gas-Sensing Property of Acid-Deposited Polyaniline Thin-Film Sensors for Detecting H2S and SO2.

Latent insulation defects introduced in manufacturing process of gas-insulated switchgears can lead to partial discharge during long-time operation, even to insulation fault if partial discharge develops further. Monitoring of decomposed components of SF6, insulating medium of gas-insulated switchgear, is a feasible method of early-warning to avoid the occurrence of sudden fault. Polyaniline thin-film with protonic acid deposited possesses wide application prospects in the gas-sensing field. Polyaniline thin-film sensors with only sulfosalicylic acid deposited and with both hydrochloric acid and sulfosalicylic acid deposited were prepared by chemical oxidative polymerization method. Gas-sensing experiment was carried out to test properties of new sensors when exposed to H2S and SO2, two decomposed products of SF6 under discharge. The gas-sensing properties of these two sensors were compared with that of a hydrochloric acid deposited sensor. Results show that the hydrochloric acid and sulfosalicylic acid deposited polyaniline thin-film sensor shows the most outstanding sensitivity and selectivity to H2S and SO2 when concentration of gases range from 10 to 100 µL/L, with sensitivity changing linearly with concentration of gases. The sensor also possesses excellent long-time and thermal stability. This research lays the foundation for preparing practical gas-sensing devices to detect H2S and SO2 in gas-insulated switchgears at room temperature.

Quantum-level investigation of air decomposed pollutants gas sensor (Pd-modified g-C3N4) influenced by micro-water content.

In the electrical industry, there are many hazardous gases that pollute the environment and even jeopardize human health, so timely detection and effective control of these hazardous gases is of great significance. In this work, the gas-sensitive properties of Pd-modified g-C3N4 interface for each hazardous gas molecule were investigated from a microscopic viewpoint, taking the hazardous gases (CO, NOx) that may be generated in the power industry as the detection target. Then, the performance of Pd-modifiedg-C3N4 was evaluated for practical applications as a gas sensor material. Novelly, an unconventional means was designed to briefly predict the effect of humidity on the adsorption properties of this sensor material. The final results found that Pd-modified g-C3N4 is most suitable as a potential gas-sensitizing material for NO2 gas sensors, followed by CO. Interestingly, Pd-modified g-C3N4 is less suitable as a potential gas-sensitizing material for NO gas sensors, but has the potential to be used as a NO cleaner (adsorbent). Unconventional simulation explorations of humidity effects show that in practical applications Pd-modified g-C3N4 remains a promising material for gas sensing in specific humidity environments. This work reveals the origin of the excellent properties of Pd-modified g-C3N4 as a gas sensor material and provides new ideas for the detection and treatment of these three hazardous gases.

Highly Sensitive Gas Sensor for Detection of Air Decomposition Pollutant (CO, NOx): Popular Metal Oxide (ZnO, TiO2)-Doped MoS2 Surface.

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 NO2) within the insulated equipment, potential insulation faults can be diagnosed. MoS2 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, MoS2 has been doped using the popular metal oxides (ZnO, TiO2) 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 MoS2 monolayer to air decomposition products. The sensing response of ZnO-MoS2 for CO at room temperature (25 °C) reaches 161.86 with a good recovery time (0.046 s). TiO2-MoS2 sensing response to NO2 reaches 3.5 × 106 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.

Transition-metal-free boron doped SbN monolayer for N2 adsorption and reduction to NH3: A first-principles study.

Electrochemical nitrogen reduction reaction (NRR) in ambient condition is an efficient and sustainable method to synthesize NH3. In this work, first-principles study was used to discuss the NRR process on B atom doped SbN monolayer. The adsorption of N2 on B-Sb17N18 and B-S18N17 was calculated including the adsorption energy, adsorption distance, and the charge density difference (CDD). Five different reaction pathways of NRR were taken into consideration and the stability of B-SbN was investigated. The results show that, because the energy of unoccupied orbital in sp3 hybridization of B atom is much lower than that in 2pz orbitals, the adsorption of N2 on B-Sb18N17 shows much larger adsorption energy (-1.01 eV with end-on pattern) compared to that of the adsorption on B-Sb17N18. For five different pathways, the 1, 2, and 4 pathways have a smaller limiting potential of about 0.52 V and the limiting step is: *N2 + H+ + e- â†’ *NNH. The 3 and 5 pathways have a larger limiting potential of 0.57 V with hydrogenation step: *NHNH2 + H+ + e- â†’ *NH2NH2. The B-Sb18N17 is structurally and thermally stable even at 500 K. Our theoretical prediction indicates that B atom substitutionally doped SbN monolayer can be a kind of high-performance metal-free NRR catalyst for NH3 synthetization, and the work provides attempts for designing and exploring 2D metal-free NRR catalysts.

Room-Temperature Detection of Perfluoroisobutyronitrile with SnO2/Ti3C2Tx Gas Sensors.

Ti3C2Tx 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 Ti3C2Tx-based gas sensors remains challenging. SnO2 is a typical semiconductor metal oxide with high reaction activity and stable chemical properties ideal for a dopant that can comprehensively improve sensing performance. Ti3C2Tx and SnO2 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 (C4F7N) with microtoxicity. A Ti3C2Tx-SnO2 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 SnO2 and Ti3C2Tx and the strong adsorption ability of SnO2 to C4F7N similar to bait for fish. We also established an actual leakage scene and demonstrated the feasibility of the Ti3C2Tx-SnO2 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 Ti3C2Tx MXene and provide a reference for maintaining C4F7N-based eco-friendly gas-insulated equipment.

SnO2 nanoparticles based highly sensitive gas sensor for detection of C4F7N: A new eco-friendly gas insulating medium.

As a novel eco-friendly gas insulation medium, perfluoroisobutyronitrile (C4F7N) has been utilized in various gas insulated equipment. Considering the biological toxicity of C4F7N, it is of great engineering significance to develop highly sensitive sensors for leakage detection scenarios. Herein, we fabricated the first SnO2 nanoparticles based highly sensitive C4F7N gas sensor that realized a superior response of 65.01% within 21 s for 50 ppm C4F7N exposure and a detection limit of 0.25 ppm. Meanwhile, successive response-recovery tests were performed to confirm its durability and stability. We also explored the sensing mechanism of SnO2 nanoparticles towards C4F7N and explained the superior sensing performance compared with other gases based on the density functional theory. It was found that the O vacancy demonstrates strong interaction with the -CN group in C4F7N that promotes the detection response, which was also confirmed by sensing experiments for SnO2 with different O vacancy density. We believe this paper provides convincing support for lowering the potential operation risk brought by C4F7N in electrical engineering and the application scenarios of SnO2 based gas sensors.

Two-dimensional square metal organic framework as promising cathode material for lithium-sulfur battery with high theoretical energy density.

Lithium-sulfur (Li-S) batteries are considered as new generation of energy storage which offer cost-effectiveness and high energy density. However, their commercialization is restricted due to a host of challenges associated with the cathode material which usually contains sulfur with several drawbacks, including a low electronic conductivity of sulfur, the 'shuttle effect', and a large volume expansion during discharge. Herein, a novel two-dimensional porphyrin-like square metal organic framework (MOF) was explored as a promising cathode material using first principles density function theory (DFT) assisted by genetic global search. The DFT results show that, among 7 kinds of transition-metal organic framework (TM-MOF), only V-MOF and Ru-MOF is found to possess considerable chemical interactions with S8 and lithium polysulfides (LiPSs) in both vacuum and in electrolytic solvents, demonstrating distinguishable anchoring performance. The genetic global search and further DFT calculations indicate that the lithiation process on V-MOF exhibited a nearly constant open-circuit voltage of about 1.92 V to 1.95 V, and the theoretical energy density could reach up to 1469 Wh kg-1 when lithiation of S8 is considered on both sides of the substrate. The volume expansion of V-MOF during discharge is found to be about 34%, much smaller than 80% for solid sulfur. The band structure and density of states of V-MOF suggest metallic properties or a small band gap for bare surface or during the lithiation process. These results indicate that two-dimensional (2D) V-MOFs can serve as high-performance cathode material with distinguished anchoring performance to block polysulfide dissolution and thereby reduce the 'shuttle effect', and help attain ultra-high energy density. Our work points the way for designing and providing experimental realization of 2D layered materials applied in cathode with high energy density and stability.

Real-Time Measurement of SO2, H2S, and CS2 Mixed Gases Using Ultraviolet Spectroscopy and a Least Squares Algorithm.

Sulfur dioxide, carbon disulfide, and hydrogen sulfide are important decomposition products of insulating gas sulfur hexafluoride, and their types and contents are of great significance for the fault diagnosis of SF6 insulated equipment. In this paper, a method of combining ultraviolet absorption spectroscopy and least squares fitting is proposed for the quantitative calculation of sulfur dioxide, carbon disulfide, and hydrogen sulfide mixed gases. All three gases have absorption peaks in the ultraviolet band and they overlap with each other which makes it hard to determinate the concentrations of the three gases directly. During the experiment, we found that high concentrations of sulfur dioxide and carbon disulfide interfered with the hydrogen sulfide calculation and the magnitude of this interference was positively correlated with these two gas concentrations. Therefore, we found a modified equation for the correction of hydrogen sulfide. Combined with this equation, accurate quantitative detection of three gases can be achieved. The detection ranges are 0.5-10 parts per million for sulfur dioxide and hydrogen sulfide, and 10-300 parts per billion for carbon disulfide. This paper provides a simple and efficient detection method, which is convenient for integration into detection equipment and it provides a support method for the diagnosis of sulfur hexafluoride decomposition gases.

Adsorption of SF6 Decomposed Products on ZnO-Modified C3N: A Theoretical Study.

SF6, as an outstanding insulation medium, is widely used in the high-voltage insulation devices, guaranteeing the safe operation of the power system. Nevertheless, the inevitable partial discharge in a long-running device causes the decomposition of SF6 and deteriorates its insulation performance. In this work, DFT calculations were performed to study the adsorbing and sensing properties of ZnO-modified C3N (ZnO-C3N) nanosheet towards SF6 decomposed products, in order to propose a novel nano-candidate for evaluating the operation status of SF6 insulation devises. We first investigated the structure of ZnO-C3N monolayer and then simulated its adsorption behaviour upon four typical SF6 decomposed species, namely H2S, SO2, SOF2, and SO2F2. It is found that the ZnO-C3N monolayer can exhibit desirable reactivity and sensitivity on SO2, SOF2, and SO2F2, leading to the intense deformation of gas molecules and large adsorption energies. These consequences allow the potential application of gas adsorbent based on ZnO-C3N monolayer for removing impurity gases from SF6 insulation equipment. According to the analysis, it is supposed that ZnO-C3N monolayer is qualified to be used in maintaining insulation strength and ensuring the safe operation of power system.

Interaction Mechanism between the C4F7N-CO2 Gas Mixture and the EPDM Seal Ring.

C4F7N (fluorinated nitrile) has been introduced as a remarkable substitute gas for the greenhouse gas SF6 (sulfur hexafluoride) which is used in gas-insulated equipment (GIE). Intensive investigations about the compatibility between C4F7N 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 C4F7N-CO2 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 C4F7N-CO2 gas mixture at temperatures higher than 70 °C. There exist chemical reactions between EPDM and C4F7N, resulting in the generation of gaseous byproducts including C3F6, CF3H, and C2F5H and corrosion of EPDM. DFT calculation also shows that the interaction between C4F7N and EPDM could cause the dissociation of C4F7N. Relevant results provide important guidance for the engineering application of the C4F7N gas mixture.

Transition metal-N4 embedded black phosphorus carbide as a high-performance bifunctional electrocatalyst for ORR/OER.

Designing highly active electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important challenge in energy conversion and storage technology. In this work, based on computational screening over doping of 23 kinds of transition metals (TMs), we use first-principles study to explore the ORR and OER activity of TM-N4 embedded black phosphorus carbide monolayer (b-PC). The results show that its catalytic performance highly depends on the number of electrons in the d orbital and the number of valence electrons of introduced TM atom. Moreover, we found that Co-N4-bPC (ηORR = 0.31 V; ηOER = 0.22 V), Rh-N4-bPC (ηORR = 0.33 V; ηOER = 0.62 V), and Ir-N4-bPC (ηORR = 0.21 V; ηOER = 0.21 V) can be promising candidates as bifunctional catalysts for both the ORR and OER and can be comparable or superior to TM-N4-graphene in terms of overpotential. They experience no structural distortion at 500 K. Moreover, the exfoliation energy of b-PC is lower than that of graphene, and these three promising candidates show much lower formation energy than TM-N4-graphene. Our study provides a systematical method for designing and developing high performance 2D material-based single atom catalysts (SACs) beyond graphene.

Repairing the N-vacancy in an InN monolayer using NO molecules: a first-principles study.

The synthesis of a perfect InN monolayer is important to achieve desirable properties for the further investigation and application of InN monolayers. However, the inevitably existing defects, such as an N-vacancy, in the synthesized InN nanomaterials would significantly impair their geometric and electronic behaviors. In this study, we proposed to repair the N-vacancy in the InN monolayer using NO molecules through NO disproportionation, which was verified to be energetically favorable according to our first-principles calculations. The repaired InN monolayer was similar to the perfect counterpart in terms of the geometric and electronic aspects. In this study, a promising strategy is presented for repairing the N-vacancy in the InN monolayer to perfect its physicochemical properties effectively, which may also be used to repair N-vacancies in other materials.

Using Pd-Doped γ-Graphyne to Detect Dissolved Gases in Transformer Oil: A Density Functional Theory Investigation.

To realize a high response and high selectivity gas sensor for the detection dissolved gases in transformer oil, in this study, the adsorption of four kinds of gases (H2, CO, C2H2, and CH4) on Pd-graphyne was investigated, and the gas sensing properties were evaluated. The energetically-favorable structure of Pd-Doped γ-graphyne was first studied, including through a comparison of different adsorption sites and a discussion of the electronic properties. Then, the adsorption of these four molecules on Pd-graphyne was explored. The adsorption structure, adsorption energy, electron transfer, electron density distribution, band structure, and density of states were calculated and analyzed. The results show that Pd prefers to be adsorbed on the middle of three C≡C bonds, and that the band gap of γ-graphyne becomes smaller after adsorption. The CO adsorption exhibits the largest adsorption energy and electron transfer, and effects an obvious change to the structure and electronic properties to Pd-graphyne. Because of the conductance decrease after adsorption of CO and the acceptable recovery time at high temperatures, Pd-graphyne is a promising gas sensing material with which to detect CO with high selectivity. This work offers theoretical support for the design of a nanomaterial-based gas sensor using a novel structure for industrial applications.

Pristine and Cu decorated hexagonal InN monolayer, a promising candidate to detect and scavenge SF6 decompositions based on first-principle study.

We carried out the first-principle study of four types of SF6 decompositions adsorbed on pristine and Cu atom decorated hexagonal InN monolayer. The adsorption structures, adsorption energy, electron transfer, band structure, density of states and desorption properties were discussed to evaluate the possible application of InN monolayer in field of adsorbent and gas sensor. The results revealed that the pristine InN monolayer has the largest adsorption energy to SO2 with evident chemical interactions. The introduction of Cu adatom on InN monolayer significantly enhanced the chemical interactions between the InN monolayer and the SO2, SOF2, SO2F2 gas molecule but declined the adsorption energy of HF. We also investigated the electronic properties of all adsorption configurations and estimated the desorption time of every gas molecule from pristine and Cu decorated InN monolayer to evaluate the potential application in noxious gas detecting and scavenging in gas insulated switch-gear (GIS).

Facile Fabrication of Au Nanoparticles/Tin Oxide/Reduced Graphene Oxide Ternary Nanocomposite and Its High-Performance SF6 Decomposition Components Sensing.

A high-performance sensor for detecting SF6 decomposition components (H2S and SOF2) was fabricated via hydrothermal method using Au nanoparticles/tin oxide/reduced graphene oxide (AuNPs-SnO2-reduced graphene oxide [rGO]) hybrid nanomaterials. The sensor has gas-sensing properties that responded and recovered rapidly at a relatively low operating temperature. The structure and micromorphology of the prepared materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Raman spectroscopy, energy-dispersive spectroscopy (EDS), and Brunauer-Emmett-Teller (BET). The gas-sensing properties of AuNPs-SnO2-rGO hybrid materials were studied by exposure to target gases. Results showed that AuNPs-SnO2-rGO sensors had desirable response/recovery time. Compared with pure rGO (210/452 s, 396/748 s) and SnO2/rGO (308/448 s, 302/467 s), the response/recovery time ratios of AuNPs-SnO2-rGO sensors for 50 ppm H2S and 50 ppm SOF2 at 110°C were 26/35 s and 41/68 s, respectively. Furthermore, the two direction-resistance changes of the AuNPs-SnO2-rGO sensor when exposed to H2S and SOF2 gas made this sensor a suitable candidate for selective detection of SF6 decomposition components. The enhanced sensing performance can be attributed to the heterojunctions with the highly conductive graphene, SnO2 films and Au nanoparticles.

Influence of Oxygen on the Thermal Decomposition Properties of C4F7N-N2-O2 as an Eco-Friendly Gas Insulating Medium.

The C4F7N (fluorinated nitrile) gas mixture has been recognized as the most potential substitute gas to SF6 used in gas-insulated equipment. In this paper, we explored the thermal stability and decomposition properties of the C4F7N-N2-O2 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 C4F7N-N2-O2 gas mixture mainly produces CO, C3F6, C3F8, CF3CN, (CN)2, and COF2. The addition of oxygen could accelerate the decomposition of C4F7N. The content of C3F6 and (CN)2 decreases, while the yield of CF4, CO, C3F8, and COF2 increases with the oxygen content. Thermal decomposition of the C4F7N-N2-O2 gas mixture at temperatures lower than 425 °C results from the interaction between C4F7N and the metal heating element, while the bond cleavage reactions occur at higher temperature. As for engineering application, the oxygen added in the 6%C4F7N-94%N2 gas mixture should not exceed 6% to avoid the negative effect of oxygen on the thermal stability of C4F7N.

Assessment on the toxicity and application risk of C4F7N: A new SF6 alternative gas.

C4F7N (fluorinated nitrile) gas mixture has been utilized as the gas insulating medium to replace the most greenhouse gas SF6 (sulphur hexafluoride). Nowadays, there are few reports on the toxicity mechanism of C4F7N and studies on the application risk of C4F7N is insufficient. In this paper, we carried out acute toxicity tests for C4F7N gas systematically. The changes of vital signs of rats after exposure to C4F7N were analyzed and the influence of C4F7N on the main organs of rats was revealed for the first time. It was found that rats developed symptoms of respiratory rate decrease, respiratory mucosa damage, movement systems impairment and abnormal blood cell count after exposure to C4F7N. Pathological section results showed that 1.5% C4F7N could damage the lung, kidney, intestine and brain tissues of rats to a certain extent, but has little influence to the eye, skin, heart and liver. The LC50 (rat, 4 h) of C4F7N gas is in the range of 15,000 ppm (1.5%) and 20,000 ppm (2%). Relevant research results not only reveal the acute toxicity mechanism of C4F7N, but also provide important reference for the safety protection of scientific researcher, equipment production, engineering operation and maintenance personnel.

Adsorption of SF6 Decomposed Products over ZnO(101Ì 0): Effects of O and Zn Vacancies.

We carried out a density functional theory study to investigate the adsorption behavior of four kinds of SF6 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 SO2 and H2S exhibits stronger chemical interactions compared to the adsorption of SOF2 and SO2F2. For SO2 and H2S adsorption, there may exist new chemical bond formation between the molecule and the surface and the H2S 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 SO2/H2S and the surface. The two-coordinated O atom (O2c) on the surface plays an important role. For SO2 and H2S adsorption, the S atom in SO2 or H2S tends to bond to the O2c 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 SF6 decomposed products by theoretical evaluation.

Apoptosis and kinematics of ejaculated spermatozoa in patients with varicocele.

Increased DNA fragmentation is found in sperm from infertile men. Varicocele is an important cause of male infertility, even though it is present in 15% of men who father children. Semen analysis does not always identify infertility in these patients. Sperm motility is strongly correlated with male fertility potential. The goal of this study was to determine the correlation between apoptosis and kinematics in the ejaculated spermatozoa of patients affected by varicocele. Fresh semen samples were obtained from 30 patients with varicocele and 15 fertile controls. These samples were compared using computer-assisted semen analysis and were assayed to determine the degree of sperm apoptosis. The apoptotic index (AI) was calculated by dividing the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine-5'-triphosphate nick end labeling (TUNEL) stained spermatozoa by the total number of Hoechst 33258-stained sperm cells for 300 sperm. Five microscopic fields were analyzed to obtain 5 AIs for each individual. Results demonstrated no significant difference in semen quality and sperm motion characteristics; however, a significantly higher AI (23.05% +/- 4.07%: mean difference +/- SE, 95% CI, 15.06%-31.03%, P <.0001) was identified in the varicocele group than in the fertile controls. We concluded that sperm apoptosis does not seem to correlate with semen quality and sperm kinematics and that apoptosis is increased in ejaculated spermatozoa in patients with varicocele compared to normal fertile men.