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Biomass is carbon-neutral and has the carbon-negative potential if combined with carbon capture and storage (CCS). This study investigated the thermochemical conversion to high-purity hydrogen of a typical lignite (BYH) and seaweed biomass (BS) with carbon capture in a designed fixed-bed reactor at moderate conditions (1 atm, 873 K). High-purity hydrogen of 486.91–801.5 ml/g-blends with suppressed CO2 formation was produced in the alkaline gasification. The alkali can decompose the coal/biomass molecular structures, in-situ capture CO2 and control the gases to high-purity H2 (80.1%–93.2%). The synergistic effect of coal and biomass changes the gas evolution behaviors and impacts the chemical structures of the char. The abundant SiO2 and Al2O3 in the coal can inhibit the catalytic activities of earth alkali metals in the biomass, but not much. These results are significant to the future development of low-carbon renewable energy techniques.

Dissolved gas analysis (DGA) is an important means of condition monitoring of oil-immersed power transformer. SnO 2 gas sensor is a common sensor for main dissolved fault characteristic gases in transformer oil, and metal doping can significantly improve its detection characteristics. However, the mechanism of metal doping modification of SnO 2 -based gas sensing materials is few and not clear yet. In this paper, the detection characteristics and sensing mechanism of metal-doped SnO 2 based sensitive materials to H 2 was systematically studied. It can be concluded that metal doping can reduce the working temperature of SnO 2 , increase the concentration characteristics of gas and accelerate the response speed. SnO 2 doped with Ag and Pd can effectively detect H 2 at concentrations below $\mathbf{1}\ \mu\mathbf{L}/\mathbf{L}$ . By comparing the microscopic simulation results with the macroscopic detection characteristics, a metal doping modification mechanism was established, which was related to the bandgap width and the optimum working temperature, gas adsorption energy and response-recovery characteristics. The accuracy and feasibility of the first-principles calculation for gas sensing mechanism analysis were verified. This research results have important theoretical and practical significance for improving the detection level of SnO 2 -based gas sensor to transformer fault characteristic gases.

As one of the most typical fault characteristic gases in transformer oil, the content of H2 is an important criterion for judging the operation state of power transformers; while online monitoring of such species through gas sensing technology could effectively detect latent faults and avoid accidents. Zinc oxide is a popular sensing material in recent years with limited sensitivity, selectivity and stability for gas detection, while zeolite imidazolate framework-8 (ZIF-8), one kind of metal–organic frameworks (MOFs) materials, possesses adjustable porosity, huge specific surface areas and good thermal stability, so it could perfectly remedy those defects. This paper studied gas-sensing properties of ZnO rods encapsulated by ZIF-8 (ZnO@ZIF-8) for H2. The morphologies, structures, and composition were characterized in detail by means of X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and energy disperse spectroscopy. H2 gas sensing properties of pure ZnO and ZnO@ZIF-8 composites were implemented based on gas sensing platform. Results suggested that the ZnO@ZIF-8 showed better sensitivity, selectivity and stability than pure ZnO rods, and meanwhile possessed lower optimum operating temperature upon H2 detection. Meanwhile the gas-sensing mechanism was analyzed comprehensively from three aspects of sensitivity, selectivity and stability. Our aim of this work is to propose a novel core–shell material with enhanced performance for H2 sensing and provide a new idea for developing high-performance materials to detect fault characteristic gases.

As a typical failure characteristic gas dissolved in transformer oil, C2H2 has a great significance to evaluate the running state of transformer by monitoring its content. Previous reports mainly focus on organizing WO3 nanoscale building blocks into well-defined 3D nanostructures. However, little attention has been paid to different 1D building blocks on the impact of gas sensing properties. In this work, nanorod and nanowire-assembled WO3 porous networks were controllably synthesized, which were applied to C2H2 detection. In comparison, sensor based on the latter exhibited superior performance than the former one, which seems indicate the significance of electronic transport in gas sensing process. It is proposed that the former possesses numerous nanojunctions between nanorods, while the latter has features with larger capping area and less junction density.

SnO2 semiconductor gas sensor as the most commonly sensors are used to check the main fault characteristic of dissolved gases in transformer oil. In current study, SnO2 rods and spheres were synthesized by the hydrothermal routes with tin salts under different conditions. We investigated the intermediate reaction on the formation of SnO2 with different morphologies and proposed their possible formation mechanisms. The structures and morphologies of this hierarchical architecture were characterized in detail by means of powder X-ray diffraction, field-emission scanning electron microscopy. Moreover, the obtained SnO2 rods are found to show the better sensing performances than the other structure with higher gas response during the response-recovery time, lower working temperature, and more sensitive response in the same concentration to carbon monoxide. Our results also illustrate that gas sensing properties of SnO2 can be significantly improved by varying the morphologies of the structures. The results may hold substantial promise in power system gas-sensing applications.

MEMS gas sensor arrays and specially designed pattern recognition systems are the main research directions in the field of modern sensing technology in the engineering, especially in the smart sensing and monitoring of faults in large power equipment such as oil-immersed transformers. In this paper, the MEMS sensor array composed by eight SWCNTs-based (pure, OH functionalized, COOH functionalized, NH2 functionalized by ethylenediamine, NH2 functionalized by aniline, Ni-coated, Pd-doped, ZnO-doped) sensing units was palced in the fault characteristic gases (H2, CO, and C2H2) of oil-immersed transformers, and their gas-sensing characteristics were tested in single and mixed gas atmosphere. Combined with the DBN-DNN pattern recognition method, the qualitative identification and quantitative analysis of the sensor array in a mixed gas atmosphere was realized, and the accuracy and reliability of the results are higher than the traditional BPNN model.

Acetylene gas (C2H2) is one of the main arc discharge characteristic gases dissolved in power transformer oil. It is of great potential to monitor the fault gas on-line by applying gas sensor technology. In this paper, gas sensors based on nanorods and nanoneedles assembled hierarchical NiO structures have been prepared. Herein, we focus on investigate the relationship between the sizes of the assembling blocking units and gas sensing properties. It can be found that the addition of CTAB/EG plays a vital role in controlling the sizes of blocking unit and assembly manner of 3D hierarchical structures. A comparison study reveals that an enhanced gas sensing performance toward C2H2 for the sensor based on nanoneedle-assembled NiO flowers occurs over that of nanorod-assembled NiO. This enhancement could be ascribed to the larger specific area of needle-flower, which provides more adsorption and desorption sites for chemical reaction as well as effective diffusion channels for C2H2. Besides, a method of calculating the specific surface area without BET testing was presented to verify the results of gas sensing measurement. The possible growth mechanism and gas sensing mechanism were discussed. Such a synthesis way may open up an avenue to tailor the morphologies and control the sizes of blocking units of some other metal oxides and enhance their gas sensing performances.

Dissolved gas analysis (DGA) is an efficient method to diagnose faults of oil-immersed power transformer in the early stages. Tin oxide $(\mathrm {S}\mathrm {n}\mathrm {O}_{2})$ has been extensively studied as a gas sensing material since it is well known to be effective in sensitively detecting various gases. However, the sensitivity of gas sensor will be deteriorated seriously when the humidity of working detecting environment changes, which makes response curve fluctuate and drifts distinctively. As humidity has a huge impact on the detection accuracy, it becomes one of the most important considerations in the practical use of sensors. In this paper, three gas sensors based on $\mathrm {S}\mathrm {n}\mathrm {O}_{2}, \mathrm {P}\mathrm {d}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ and $\mathrm {Z}\mathrm {n}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ sensing materials were synthesized by hydrothermal method and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). Meanwhile, the performance of the gas-sensing under different environmental humidity was tested. The results show that metal doped gas sensors are better sensitivity and stability than that of the pure $\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ gas sensor. Moreover, with the increase of humidity the detection sensitivity of $\mathrm {P}\mathrm {d}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ and $\mathrm {Z}\mathrm {n}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ sensors emerge a phenomenon of increasing first and decreasing then. Ultimately, based on the sensing properties of pure, Pd and Zn-doped gas sensors, the possible sensing mechanism for them in humid atmosphere was investigated, which will make contribution to the application of $\mathrm {S}\mathrm {n}\mathrm {O}_{2}$-based gas sensors in the online monitoring of dissolved gases in transformer oil.

Acetylene (C 2 H 2 ) is one of the most important and typical characteristic fault gas dissolved in power transformer oil, and on-line monitoring its concentration could reflect the operational state of transformer timely, which could prevent safety issues of power grid effectively. Considering the traditional zinc oxide (ZnO) gas sensor exhibiting some shortcomings, such as higher operating temperature, lower response, poor selectivity, and so on. The paper proposes the ZnO-based (pure ZnO, cobalt-doped ZnO) gas sensors to contrastively study. The characterization results of nanomaterials (XRD, FESEM, HRTEM) show that the as-grown products possess the good crystal structure and high purity. The gas-sensing experiment results on optimum working temperature (Co-ZnO: 160 °C, pure ZnO: 180 °C), response-recovery time (Co-ZnO: 30–33 s, pure ZnO: 35–51 s), sensitivity (Co-ZnO: 9.886, pure ZnO: 1.971; 200 ppm C 2 H 2 ), the limit of detection (3 ppm, Co-ZnO), stability (20, 50, 100, 200, 400 ppm C 2 H 2 ), and selectivity (H 2 , CH 4 , C 2 H 2 , C 2 H 4 ; 50, 100, 200 ppm) are obtained. They correspond to the theoretically analysis which based on the DFT-D calculations. The result of gas-sensing properties indicates that the dopant of Co is beneficial to reduce the optimum working temperature and response-recovery time significantly. In addition, it enhances the sensitivity of gas sensor evidently and process a good stability as well as selectivity. The orbital hybridization occurred during C 2 H 2 adsorption, which promotes the electron transfer and conductivity changes. The results lay a solid foundation for the preparation of new ZnO-based gas sensor that serve for the transformer condition monitoring and fault diagnosis.

Pure and Ni doped ZnO nanorods were successfully synthesised via a simple hydrothermal synthesis method and characterised by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM respectively. Sensing properties were systematically measured towards acetylene gas (C2H2). The Ni doped ZnO gas sensor exhibits excellent gas sensing performances, such as lower working temperature, higher gas response, rapid response and recovery time, than those of pure ZnO gas sensors. All results demonstrate the potential of Ni dopant for improving the gas sensing properties of ZnO gas sensors to C2H2 gas.

The detection of partial discharge and analysis of the composition and content of sulfur hexafluoride SF6 gas components are important to evaluate the operating state and insulation level of gas-insulated switchgear (GIS) equipment. This paper reported a novel sensing material made of pure ZnO and NiO-decorated ZnO nanoflowers which were synthesized by a facile and environment friendly hydrothermal process for the detection of SF6 decomposition byproducts. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the structural and morphological properties of the prepared gas-sensitive materials. Planar-type chemical gas sensors were fabricated and their gas sensing performances toward the SF6 decomposition byproducts SO2, SO2F2, and SOF2 were systemically investigated. Interestingly, the sensing behaviors of the fabricated ZnO nanoflowers-based sensor to SO2, SO2F2, and SOF2 gases can be obviously enhanced in terms of lower optimal operating temperature, higher gas response and shorter response-recovery time by introducing NiO. Finally, a possible gas sensing mechanism for the formation of the p–n junctions between NiO and ZnO is proposed to explain the enhanced gas response. All results demonstrate a promising approach to fabricate high-performance gas sensors to detect SF6 decomposition byproducts.

Acetylene (C2H2) gas sensors were developed by synthesizing a reduced graphene oxide (rGO)-loaded SnO2 hybrid nanocomposite via a facile two-step hydrothermal method. Morphological characterizations showed the formation of well-dispersed SnO2 nanoparticles loaded on the rGO sheets with excellent transparency and obvious fold boundary. Structural analysis revealed good agreement with the standard crystalline phases of SnO2 and rGO. Gas sensing characteristics of the synthesized materials were carried out in a temperature range of 100–300 °C with various concentrations of C2H2 gas. At 180 °C, the SnO2–rGO hybrid showed preferable detection of C2H2 with high sensor response (12.4 toward 50 ppm), fast response-recovery time (54 s and 23 s), limit of detection (LOD) of 1.3 ppm and good linearity, with good selectivity and long-term stability. Furthermore, the possible gas sensing mechanism of the SnO2–rGO nanocomposites for C2H2 gas were summarized and discussed in detail. Our work indicates that the addition of rGO would be effective in enhancing the sensing properties of metal oxide-based gas sensors for C2H2 and may make a contribution to the development of an excellent ppm-level gas sensor for on-line monitoring of dissolved C2H2 gas in transformer oil.

The operation conditions of oil immersed power transform will affect the safety and stability of power system directly. As one of the main fault characteristic gases dissolved in transformer oil, acetylene (C 2 H 2 ) gas can effectively reflect the discharge faults which occur in oil-paper insulation system. Monitoring its content of C 2 H 2 gas has a great significance in diagnosis and evaluation the running state of transformer. In this paper, tin oxide (SnO 2 ) and reduced graphene oxide (rGO) nanocomposite based C 2 H 2 gas sensor was developed. The gas sensing material was synthesized by a facile hydrothermal method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM). Then, the gas sensing properties of as-synthesized nanomaterials were tested by exposing to different concentration of C 2 H 2 gas with a temperature range of 100–300 °C and its gas sensing mechanism of C 2 H 2 gas was discussed. The characterization results indicated that the SnO 2 and SnO 2 /rGO were succeed synthesized. Under the optimum operating temperature (180 °C) of SnO 2 /rGO, it exhibited a low detection limit (1 μL/L), high response (50 ppm, 13.2) and good linearity (1–10 μL/L). The gas sensing mechanism for the better sensing properties to C 2 H 2 gas was explained based on superhigh surface areas and heterojunction between SnO 2 and rGO. This results highlight SnO 2 /rGO can effective enhance the C2H2 gas sensing properties for monitoring the dissolved C 2 H 2 gas in transformer oil with high performances.

Methane, ethane, ethylene and acetylene are the effective failure characteristic gases for power transformer, which can effectively reflect the electric and overheat faults. Monitoring these gases have a great significance in diagnosis and evaluation the running state of transformer. In this paper, Ptdoped SnO 2 nanoflower gas sensor was prepared, then its detection characteristic and response mechanism of hydrocarbon gases had been studied. The results indicated that, as the increasing of specific surface area, compared to the pure SnO 2 nanoparticle gas sensor, the Pt-doped SnO 2 nanoflower gas sensor has higher sensitivity and faster response characteristic to hydrocarbon gases, and responses versus gas concentration kept a good linearity when the gas concentration between 5 μL/L and 50 μL/L. The role of the dopant of Pt into the SnO 2 and the sensing mechanism had also been discussed in this work.

H 2 is one of the main fault characteristic gases dissolved in transformer oil, which can indicate the electric faults, such as high energy discharge, spark discharge and partial discharge, and partial oil overheating phenomenon. Detection the content of H 2 has an important significance for transformer diagnosis and state assessment. Gas sensing detection technology is the core of online monitoring device. In this paper, for the detection of dissolved H 2 , based on the density functional theory and the first-principles, pure and Ag-doped SnO 2 models and gas adsorption models were built, and theoretical calculations were conducted. Meanwhile, pure and Ag-doped SnO 2 gas sensing materials were synthesized with hydrothermal method. Then SnO 2 based gas sensors were fabricated and their gas sensing properties were measured. Finally, its gas sensing mechanism was discussed based on the macro gas sensing properties and micro simulating calculations. The results indicated that, Ag doping can improve the gas sensing properties of SnO 2 nanostructures to H 2 , Ag doping sensor has better effect than pure sensor for H 2 detection, such as a lower optimum operating temperature of 340 °C, lower detection limit of 10 µL/L with higher sensitivity. The role of the dopant of Ag into the SnO 2 and the sensing mechanism had also been discussed in this work. The experimental results verifies the feasibility and accuracy of study the gas sensing performances of SnO 2 based gas sensors using the first-principles calculation based on the density functional theory, further perfecting its gas sensing mechanism of SnO 2 based gas sensor and providing us a fresh idea and feasible way to develop different kinds dopant of metal or metal-oxide gas sensors with high performances.