Gas-Sensitive Performance Study of Metal (Au, Pd, Pt)/ZnO Heterojunction Gas Sensors for Dissolved Gases in Transformer Oil.

An oil-immersed transformer is a critical electrical device for power delivery. Online monitoring of transformer operation is the key to ensuring the regular operation of power systems. This paper proposes Au/ZnO, Pd/ZnO, and Pt/ZnO heterojunctions as new gas-sensitive materials and investigates their gas-sensitive performance to dissolved gases (C2H4, CO, and H2) in transformer oil. Upon theoretical density functional theory (DFT) calculations, the analysis of the total density of states (TDOS), partial density of states (PDOS), molecular orbital theory, and charge deformation density reveals that Au, Pd, and Pt form heterojunctions with ZnO, which enhance the electrical conductivity of the system. Meanwhile, intrinsic ZnO is unsuitable for gas detection and adsorption, while the Au/ZnO heterojunction suits C2H4 detection. In contrast, the Pd/ZnO heterojunction is suitable for H2 detection, and the Pt/ZnO heterojunction is suitable for C2H4 and CO detection. The electrical conductivity of the adsorption models is changed to varying degrees after gas adsorption. The different change rate electrical conductivity just serves as a theoretical foundation for determining the type and concentration of dissolved gases in transformer oil. The research results act as a theoretical foundation for constructing gas sensors with a ZnO-based material.

DFT Study of Metal (Ag, Au, Pt)-Modified SnS2 for Adsorption of SF6 Decomposition Gases in Gas-Insulated Switchgear.

In this study, the gas-sensitive response of metal (Ag, Au, Pt)-modified SnS2 toward SF6 decomposition gases (SOF2, SO2F2, SO2, H2S) in gas-insulated switchgear was studied by analyzing the adsorption structure, band structure, charge transfer, and density of states based on density functional theory. The results show that the adsorption of the four target gases on pristine SnS2 belongs to weak physical adsorption. Compared with the pristine SnS2, the adsorption energy of the transition metal atom-modified SnS2 monolayer has been improved to a certain extent and the adsorption capacity of these four gases on the transition metal atom-modified SnS2 monolayer has obviously improved. Moreover, the recovery time of Ag-SnS2/SOF2, Ag-SnS2/SO2F2, Au-SnS2/SOF2, Au-SnS2/SO2F2, and Pt-SnS2/SO2F2 is too short, indicating that these conditions have poor adsorption capacity and sensitivity to SF6 decomposition gases and are not suitable as detection materials for these gases. According to the different changes in conductivity during adsorption, it provides a feasible solution to detect each SF6 decomposition gas. This theoretical study effectively explained the adsorption and sensing properties between the metal-modified monolayers and gases.

Gas-Sensing Performance of Metal Oxide Heterojunction Materials for SF6 Decomposition Gases: A DFT Study.

The online monitoring of GIS equipment can be realized through detecting SF6 decomposition gasses. Metal oxide heterojunctions are widely used as gas-sensing materials. In this study, the structural and electrical properties of In2O3-ZnO and TiO2-ZnO heterojunctions were analyzed based on density functional theory calculations. After heterojunction structural optimization, the electrical conductivity of these two heterojunctions was enhanced compared to each intrinsic model, and the electrical conductivity is ranked as follows: In2O3-ZnO heterojunction > TiO2-ZnO heterojunction. The gas-sensing response of these two heterojunctions to four SF6 decomposition gasses, H2S, SO2, SOF2, and SO2F2, was investigated. For gas adsorption systems, the adsorption energy, charge transfer, density of states, charge difference density, and frontier molecular orbitals were calculated to analyze the adsorption and gas-sensing performance. For gas adsorption on the In2O3-ZnO heterojunction surface, the induced conductivity changes are in the following order: H2S > SO2F2 > SOF2 > SO2. For gas adsorption on the TiO2-ZnO heterojunction surface, H2S and SOF2 increase conductivity, and SO2 and SO2F2 decrease conductivity.

Adsorption and Sensing Performances of a TiO2 Cluster-Doped Graphene Monolayer toward SOF2 and SO2F2.

Due to the high surface activity of metal atoms, it is difficult for doped metals to maintain long-term stability. Compared with other metal oxides, TiO2 graphene sensors have a higher sensing response and a larger specific surface area. However, there is currently no literature comparing and analyzing the effect of graphene-doped TiO2 on the adsorption performance of SF6 decomposition components. Therefore, this article investigated the adsorption performance of SF6 decomposition products: the distribution of SOF2 and SO2F2 on nTiO2 (n = 1,2,3)-doped graphene. In order to explore the interaction mechanism between gas molecules and these modified systems, their Eads, charge transfer, DOS, and PDOS were systematically studied. The doping of nTiO2 significantly improves the adsorption ability of graphene to gas molecules, discovers and enriches the online monitoring methods of GIS, and improves the engineering application value of 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.

Micro-scale effects of nano-SiO2 modification with silane coupling agents on the cellulose/nano-SiO2 interface.

In this study, molecular dynamics simulations were used to investigate the micro-scale effects of modification of nano-SiO2 with commonly used silane coupling agents (KH550, KH560, KH570, and KH792) on the cellulose/nano-SiO2 interface. The relative optimum silane coupling agent and grafting density for nano-SiO2 modification to improve the cellulose/nano-SiO2 interface were determined. The results showed that at the same grafting density, modification of nano-SiO2 with KH792 yielded the highest interfacial binding energy and binding energy density, the largest number of hydrogen bonds at the cellulose/nano-SiO2 interface, the strongest binding to the cellulose chains, and the largest overlapping area at the cellulose/nano-SiO2 interface. We found that the non-bonding interaction energy played a decisive role in the energy of the model system and the interfacial interaction force mainly consisted of van der Waals forces and the hydrogen-bonding energy. When silane coupling agents with amino groups (KH550 and KH792) were used to modify nano-SiO2, the number of hydrogen bonds at the cellulose/nano-SiO2 interface was larger than that for unmodified nano-SiO2. When silane coupling agents without amino groups (KH560 and KH570) were used to modify nano-SiO2, the number of hydrogen bonds at the cellulose/nano-SiO2 interface was lower than the case for unmodified nano-SiO2. Nano-SiO2 modification with various amounts of KH792 was investigated. The results showed that the interfacial bonding energy increased with grafting density. When the grafting density was 1.57 nm-2, the interfacial bonding energy and number of hydrogen bonds formed at the cellulose/nano-SiO2 interface was relatively stable, which indicates that the interface had reached a relatively stable state. Modification of nano-SiO2 with KH792 achieved the greatest improvement of the cellulose/nano-SiO2 interface; this interface reached a relatively stable state when the grafting density of KH792 was 1.57 nm-2.

Ni-CNT Chemical Sensor for SF6 Decomposition Components Detection: A Combined Experimental and Theoretical Study.

SF6 decomposition components detection is a key technology to evaluate and diagnose the insulation status of SF6-insulated equipment online, especially when insulation defects-induced discharge occurs in equipment. In order to detect the type and concentration of SF6 decomposition components, a Ni-modified carbon nanotube (Ni-CNT) gas sensor has been prepared to analyze its gas sensitivity and selectivity to SF6 decomposition components based on an experimental and density functional theory (DFT) theoretical study. Experimental results show that a Ni-CNT gas sensor presents an outstanding gas sensing property according to the significant change of conductivity during the gas molecule adsorption. The conductivity increases in the following order: H2S > SOF2 > SO2 > SO2F2. The limit of detection of the Ni-CNT gas sensor reaches 1 ppm. In addition, the excellent recovery property of the Ni-CNT gas sensor makes it easy to be widely used. A DFT theoretical study was applied to analyze the influence mechanism of Ni modification on SF6 decomposition components detection. In summary, the Ni-CNT gas sensor prepared in this study can be an effective way to evaluate and diagnose the insulation status of SF6-insulated equipment online.

Synthesis of Graphene-Based Sensors and Application on Detecting SF6 Decomposing Products: A Review.

Graphene-based materials have aroused enormous focus on a wide range of engineering fields because of their unique structure. One of the most promising applications is gas adsorption and sensing. In electrical engineering, graphene-based sensors are also employed as detecting devices to estimate the operation status of gas insulated switchgear (GIS). This paper reviews the main synthesis methods of graphene, gas adsorption, and sensing mechanism of its based sensors, as well as their applications in detecting SF6 decomposing products, such as SO2, H2S, SO2F2, and SOF2, in GIS. Both theoretical and experimental researches on gas response of graphene-based sensors to these typical gases are summarized. Finally, the future research trend about graphene synthesis technique and relevant perspective are also given.

Design of a New Built-in UHF Multi-Frequency Antenna Sensor for Partial Discharge Detection in High-Voltage Switchgears.

In this study a new built-in ultrahigh frequency (UHF) antenna sensor was designed and applied in a high-voltage switchgear for partial discharge (PD) detection. The casing of the switchgear was initially used as the ground plane of the antenna sensor, which integrated the sensor into the high-voltage switchgear. The Koch snowflake patch was adopted as the radiation patch of the antenna to overcome the disadvantages of common microstrip antennas, and the feed position and the dielectric layer thickness were simulated in detail. Simulation results show that the antenna sensor possessed four resonant points with good impedance matching from 300 MHz to 1000 MHz, and it also presented good multi-frequency performance in the entire working frequency band. PD detection experiments were conducted in the high-voltage switchgear, and the fabricated antenna sensor was effectively built into the high-voltage switchgear. In order to reflect the advantages of the built-in antenna sensor, another external UHF antenna sensor was used as a comparison to simultaneously detect PD. Experimental results demonstrated that the built-in antenna sensor possessed high detection sensitivity and strong anti-interference capacity, which ensured the practicability of the design. In addition, it had more high-voltage switchgear PD detection advantages than the external sensor.

Gas Sensing Analysis of Ag-Decorated Graphene for Sulfur Hexafluoride Decomposition Products Based on the Density Functional Theory.

Detection of decomposition products of sulfur hexafluoride (SF6) is one of the best ways to diagnose early latent insulation faults in gas-insulated equipment, and the occurrence of sudden accidents can be avoided effectively by finding early latent faults. Recently, functionalized graphene, a kind of gas sensing material, has been reported to show good application prospects in the gas sensor field. Therefore, calculations were performed to analyze the gas sensing properties of intrinsic graphene (Int-graphene) and functionalized graphene-based material, Ag-decorated graphene (Ag-graphene), for decomposition products of SF6, including SO2F2, SOF2, and SO2, based on density functional theory (DFT). We thoroughly investigated a series of parameters presenting gas-sensing properties of adsorbing process about gas molecule (SO2F2, SOF2, SO2) and double gas molecules (2SO2F2, 2SOF2, 2SO2) on Ag-graphene, including adsorption energy, net charge transfer, electronic state density, and the highest and lowest unoccupied molecular orbital. The results showed that the Ag atom significantly enhances the electrochemical reactivity of graphene, reflected in the change of conductivity during the adsorption process. SO2F2 and SO2 gas molecules on Ag-graphene presented chemisorption, and the adsorption strength was SO2F2 > SO2, while SOF2 absorption on Ag-graphene was physical adsorption. Thus, we concluded that Ag-graphene showed good selectivity and high sensitivity to SO2F2. The results can provide a helpful guide in exploring Ag-graphene material in experiments for monitoring the insulation status of SF6-insulated equipment based on detecting decomposition products of SF6.

CuO/TiO2/MXene-Based Sensor and SMS-TENG Array Integrated Inspection Robots for Self-Powered Ethanol Detection and Alarm at Room Temperature.

In this study, a high-precision CuO/TiO2/MXene ethanol sensor operating at room temperature was prepared. The sensor exhibits excellent response value (95% @1 ppm ethanol), extremely low detection limit (0.3 ppm), fast response/recovery time (16/13 s), and remarkable long-term stability for trace detection of ethanol gas at room temperature, attributed to the p-n heterojunction formed by CuO and TiO2, as well as the rich functional groups and large specific surface area of MXene. Furthermore, a high-performance triboelectric nanogenerator (SMS-TENG) was developed through the introduction of the silicone/Mxene@silicone dual dielectric layer as the triboelectric layer, which improves the charge storage capacity of the dielectric layer and greatly enhances the output performance of the TENG. At the optimal doping ratio, the open-circuit voltage of the SMS-TENG can reach 1160 V, which is sufficient to light 720 LEDs. By combining the sensor and SMS-TENG, the resistive response of ethanol sensing is converted to a voltage response, which amplifies the response value up to 15.8 times. Finally, the designed SMS-TENGs are expected to be arrayed on an inspection robot as energy supply and combined with the CuO/TiO2/Mxene ethanol sensor to build a self-powered ethanol detection alarm system, endowing the inspection robot with the capability of self-powered ethanol detection at ppb level. This work provides an effective pathway for the intelligence of ethanol detection.

Adsorption Characteristics of H2S and SO2 Gases on Cu2O Cluster-Modified Graphene Monolayer for Gas-Sensing Applications.

In this study, the adsorption capability and gas-sensing performance of Cu2O-graphene on SF6-featured decomposers (H2S and SO2) were evaluated based on first-principles calculations. The most stable structure, adsorption energy, band structure, and DOS and PDOS were used to investigate the adsorption mechanism. The findings suggest that all adsorption systems are exothermic and spontaneous. The density of states analysis suggests that the adsorption of H2S and SO2 is chemisorbed. The recovery time shows that the desorption time after H2S adsorption is shorter at a suitable temperature. In contrast, the desorption time of SO2 was quite long in some systems, which reduced the detection efficiency. In summary, Cu2O-graphene could be a promising gas-sensing material for the detection of two-characteristic SF6-decomposition products.

Co3O4@TiO2@Y2O3 nanocomposites for a highly sensitive CO gas sensor and quantitative analysis.

In order to predict the early failure of organic insulator, Co3O4@TiO2@Y2O3 nanocomposites was prepared and characterized (XRD, SEM, EDS, FTIR, UV-vis-NIR, XPS) to detect decomposition CO gas. A simple experimental platform was built to verify the excellent adsorption, stability, selectivity and repeatability of the composite. Then, the mechanism of adsorption enhancement was analyzed by heterojunction. Aiming at 170 sets of gas sensing data sets, Successive Projections Algorithm (SPA) was used to extract data features, and grey wolf optimization vector machine regression (GWO-SVR) model was established to predict carbon monoxide concentration. The correlation coefficient (RP), root mean square error (RMSEP) and calculation time of prediction set were 99.3025%, 0.0418 and 1.47 s, respectively. Therefore, the combination of the superior properties of a composite sensitive material and the small sample quantitative prediction model is a promising method for gas sensors in the future.

Adsorption and Gas-Sensing Properties of Agn (n = 1-4) Cluster Doped GeSe for CH4 and CO Gases in Oil-Immersed Transformer.

The adsorption mechanism of CO and CH4 on GeSe, modified with the most stable 1-4 Ag-atom clusters, is studied with the help of density functional theory. Adsorption distance, adsorption energy, total density of states (TDOS), projected density of states (PDOS), and molecular orbital theory were all used to analyze the results. CO was found to chemisorb exothermically on GeSe, independent of Ag cluster size, with Ag4-GeSe representing the optimum choice for CO gas sensors. CH4, in contrast, was found to chemisorb on Ag-GeSe and Ag2-GeSe and to physisorb on Ag3-GeSe and Ag4-GeSe. Here, Ag GeSe was found to be the optimum choice for CH4 gas sensors. Overall, our calculations suggest that GeSe modified by Ag clusters of different sizes could be used to advantage to detect CO and CH4 gas in ambient air.

Adsorption of Greenhouse Decomposition Products on Ag2O-SnS2 and CuO-SnS2 Surfaces.

In this paper, based on density functional theory, the adsorption mechanism and gas sensitivity of Ag2O/CuO-modified SnS2 were analyzed. The results were analyzed according to the adsorption energy, total density of states, partial density of states, and frontier molecular orbital theory. The results show that the adsorption of all gas molecules is exothermic. NH3, Cl2, and C2H2 gases are chemisorbed on the modified SnS2 surfaces. After gas adsorption, the energy gap of the base changes by more than 10%, which fully shows that the conductivity changes greatly after gas adsorption, which can be reflected in the macroscopic resistance change. Ag2O-SnS2 is suitable as a gas sensor for NH3 gas sensors in terms of moderate adsorption distance, large adsorption energy, charge transfer, and frontier molecular orbital theory, while CuO-SnS2 is more suitable as a C2H2 gas sensor.

Gas-Sensing Properties of B/N-Modified SnS2 Monolayer to Greenhouse Gases (NH3, Cl2, and C2H2).

The adsorption capacity of intrinsic SnS2 to NH3, Cl2 and C2H2 is very weak. However, non-metallic elements B and N have strong chemical activity, which can significantly improve the conductivity and gas sensitivity of SnS2. Based on density functional theory, SnS2 was modified with B and N atoms to analyze its adsorption mechanism and gas sensitivity for NH3, Cl2 and C2H2 gases. The optimal structure, adsorption energy, state density and frontier molecular orbital theory are analyzed, and the results are in good agreement with the experimental results. The results show that the adsorption of gas molecules is exothermic and spontaneous. Only the adsorption of NH3 and Cl2 on B-SnS2 belongs to chemical adsorption, whereas other gas adsorption systems belong to physical adsorption. Moderate adsorption distance, large adsorption energy, charge transfer and frontier molecular orbital analysis show that gas adsorption leads to the change of the conductivity of the modified SnS2 system. The adsorption capacity of B-SnS2 to these gases is Cl2 > NH3 > C2H2. The adsorption capacity of N-SnS2 is NH3 > C2H2 > Cl2. Therefore, according to different conductivity changes, B-SnS2 and N-SnS2 materials can be developed for greenhouse gas detection of gas sensors.

Gas-Sensing Properties of Cu2S-MoSe2 Nanosheets to NO2 and NH3 Gases.

Cu2S-MoSe2 was selected as a gas-sensing material to detect NO2 and NH3. Based on density functional theory calculations, the adsorption structures, density of states, molecular orbit, and recovery time were studied to analyze the gas-sensing mechanism of Cu2S-MoSe2 to gases. Calculation results show that Cu2S clusters receive a stable doping structure on the MoSe2 surface. Compared with intrinsic MoSe2, Cu2S-MoSe2 shows more excellent adsorption performance to NO2 and NH3 due to the active feature of the Cu2S dopant. After NO2 and NH3 adsorption, the energy gap decreases, indicating an improvement of the conductivity, which is greatly significant for gas sensing. For double NH3 adsorption, the conductivity of the entire system increases more than that of a double NO2 adsorption system, signifying the sensitivity of Cu2S-MoSe2 is greater for NH3 than NO2. The results of theoretical recovery time show that Cu2S-MoSe2 is sensitive for NH3 detection at room temperature (298 K) and NO2 detection at high temperature (400 K).

First-Principles Insight into a Ru-Doped SnS2 Monolayer as a Promising Biosensor for Exhale Gas Analysis.

Realizing the diagnosis of lung cancer at an inchoate stage is significant to get valuable time to conduct curative surgery. In this work, we relied on a density functional theory (DFT)-proposed Ru-SnS2 monolayer as a novel, promising biosensor for lung cancer diagnosis through exhaled gas analysis. The results indicated that the Ru-SnS2 monolayer has admirable adsorption performance for three typical volatile organic compounds (VOCs) of lung cancer patients, which therefore results in a remarkable change in the electronic behavior of the Ru-doped surface. As a consequence, the conductivity of the Ru-SnS2 monolayer increases after gas adsorption based on frontier molecular orbital theory. This provides the possibility to explore the Ru-SnS2 monolayer as a biosensor for lung cancer diagnosis at an early stage. In addition, the desorption behavior of three VOCs from the Ru-SnS2 surface is studied as well. Our calculations aim at proposing novel sensing nanomaterials for experimentalists to facilitate the progress in lung cancer prognosis.

Au Catalyst-Modified MoS2 Monolayer as a Highly Effective Adsorbent for SO2F2 Gas: A DFT Study.

To ensure the stable operation of gas-insulated equipment, removal of SF6 decomposition products of sulfur hexafluoride (SF6) is one of the best methods. SO2F2 is one of the typical decomposition products of SF6, while the Au-modified MoS2 (Au-MoS2) monolayer is a novel gas adsorbent. Therefore, based on the first-principles calculation, the adsorption properties of the SO2F2 molecule on the Au-MoS2 monolayer are calculated. Furthermore, the adsorption energy, charge transfer, and structure parameters were analyzed to obtain the most stable adsorption structure. These results indicate that all of the adsorption processes are exothermic. To better study the adsorption mechanism between the SO2F2 molecule and the Au-MoS2 monolayer, the density of states, the highest occupied molecular orbital, the lowest unoccupied molecular orbital, and electron density difference were obtained. At last, we conclude that the interaction between the SO2F2 molecule and the Au-MoS2 monolayer was chemisorption. This study provides a theoretical basis to prepare the Au-MoS2 monolayer for the removal of SF6 decomposition products.

Pt Cluster Modified h-BN for Gas Sensing and Adsorption of Dissolved Gases in Transformer Oil: A Density Functional Theory Study.

Hexagonal-Boron nitride nanotubes (h-BN) decorated with transition metals have been widely studied due to their enhanced physicochemical properties. In this paper, Pt cluster-modified h-BN is proposed as a sensitive material for a novel gas sensor for the online malfunction monitoring of oil-immersed transformers. The inner oil is ultimately decomposed to various gases during the long-term use of oil-immersed transformers. Exposure to excessively high temperatures produces the alkanes CH4 and C2H6, whereas different degrees of discharge generate H2 and C2H2. Therefore, the identification of H2, CH4, and C2H2 gas efficiently measures the quality of transformers. Based on the density functional theory, the most stable h-BN doped with 1-4 Pt atoms is employed to simulate its adsorption performance and response behavior to these typical gases. The adsorption energy, charge transfer, total density of states, projected density of states, and orbital theory of these adsorption systems are analyzed and the results show high consistency. The adsorption ability for these decomposition components are ordered as follows: C2H2 > H2 > CH4. Pt cluster-modified h-BN shows good sensitivity to C2H2, H2, with decreasing conductivity in each system, but is insensitive to CH4 due to its weak physical sorption. The conductivity change of Ptn-h-BN is considerably larger upon H2 than that upon C2H2, but is negligible upon CH4. Our calculations suggest that Pt cluster modified h-BN can be employed in transformers to estimate their operation status.