Hierarchical flower-like ZnO nanorods, net-like ZnO nanofibers and ZnO nanobulks have been successfully synthesized via a surfactant assisted hydrothemal method. The synthesized products were characterized by X-ray powder diffraction and field emission scanning electron microscopy, respectively. A possible growth mechanism of the various hierarchical ZnO nanostructures is discussed in detail. Gas sensors based on the as-prepared ZnO nanostructures were fabricated by screen-printing on a flat ceramic substrate. Furthermore, their gas sensing characteristics towards methane were systematically investigated. Methane is an important characteristic hydrocarbon contaminant found dissolved in power transformer oil as a result of faults. We find that the hierarchical flower-like ZnO nanorods and net-like ZnO nanofibers samples show higher gas response and lower operating temperature with rapid response-recovery time compared to those of sensors based on ZnO nanobulks. These results present a feasible way of exploring high performance sensing materials for on-site detection of characteristic fault gases dissolved in transformer oil.

Nano‐SnO₂ powder was prepared by the hydrothermal method in this paper. X‐ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the composition of the crystalline phase and the morphology of the prepared gas‐sensitive materials, respectively. In particular, the study focused on the sensing behaviors of nano‐SnO₂‐based sensor towards power transformer fault gases such as hydrogen and carbon monoxide. The optimum working temperature for hydrogen and carbon monoxide is about 400^∘C and 360^∘C, separately. Further investigations into the adsorption process of gas molecule on SnO₂ (110) surface based on the first principles were conducted. The calculations indicated that 1σ orbits of H₂ split into several new electronic peaks and 5σ orbits of CO almost degenerated completely in the adsorption process, which promoted charge transfer between gas molecule and SnO₂ (110) surface. It provides a qualitative explanation for the prepared nano‐SnO₂‐based sensor exhibiting different gas sensing properties towards H₂ and CO.

Methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄), and acetylene (C₂C₂) are important fault characteristic hydrocarbon gases dissolved in power transformer oil. Online monitoring these gaseous components and their generation rates can present the operational state of power transformer timely and effectively. Gas sensing technology is the most sticky and tricky point in online monitoring system. In this paper, pure and Pd‐doped SnO₂ nanoparticles were synthesized by hydrothermal method and characterized by X‐ray powder diffraction, field‐emission scanning electron microscopy, and energy dispersive X‐ray spectroscopy, respectively. The gas sensors were fabricated by side‐heated preparation, and their gas sensing properties against CH₄, C₂H₆, C₂H₄, and C₂H₂ were measured. Pd doping increases the electric conductance of the prepared SnO₂ sensors and improves their gas sensing performances to hydrocarbon gases. In addition based on the frontier molecular orbital theory, the highest occupied molecular orbital energy and the lowest unoccupied molecular orbital energy were calculated. Calculation results demonstrate that C₂H₄ has the highest occupied molecular orbital energy among CH₄, C₂H₆, C₂H₄, and C₂H₂, which promotes charge transfer in gas sensing process, and SnO₂ surfaces capture a relatively larger amount of electric charge from adsorbed C₂H₄.

SnO₂ nanoparticles were synthesized through the sol–gel method, meanwhile, the thick film sensors were prepared with the method of polymethyl-methacrylate PMMA pore-forming and silk screen printing. In this paper, SEM and XRD measurements were employed to represent the structure and morphology of the synthesized SnO₂ respectively. With the use of electricity chemical workstation, hydrogen gas sensitive properties were tested. It turns out that the average grain diameter of the SnO₂ particle with the structure of tetragonal phase is 60 nm. Along with the increase of the addition of the PMMA concentration, the conductivity of SnO₂ reduces significantly, but the response time and recovery time have no obvious change. The effect law of working temperature and sintering temperature on SnO₂ response and recovery time was also explored. With the rise of temperature the response time shortens and the recovery time has no obvious change. Moreover, with the increase of the sintering temperature, SnO₂ has no clear influence on the response time of H₂. However, the recovery time of H₂ shortens obviously.

Co‐doped SnO₂ nanofibers were successfully synthesized via electrospinning method, and Co‐doped SnO₂ nanospheres were also prepared with traditional hydrothermal synthesis route for comparison. The synthesized SnO₂ nanostructures were characterized by X‐ray powder diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy, and X‐ray photoelectron spectra. Planar‐type chemical gas sensors were fabricated and their sensing properties to methane were investigated in detail. Gas sensors based on these two samples demonstrate the highest CH₄ sensing response at an operating temperature of 300°C. Compared with traditional SnO₂ nanospheres, the nanofiber sensor shows obviously enhanced gas response, higher saturated detection concentration, and quicker response‐recovery time to methane. Moreover, good stability, prominent reproducibility, and excellent selectivity are also observed based on the nanofibers. These results demonstrate the potential application of Co‐doped SnO₂ nanofibers for fabricating high performance methane sensors.

Various morphologies of low dimensional ZnO nanostructures, including spheres, rods, sheets, and wires, were successfully synthesized using a simple and facile hydrothermal method assisted with different surfactants. Zinc acetate dihydrate was chosen as the precursors of ZnO nanostructures. We found that polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), glycine, and ethylene glycol (EG) play critical roles in the morphologies and microstructures of the synthesized nanostructures, and a series of possible growth processes were discussed in detail. Gas sensors were fabricated using screen-printing technology, and their sensing properties towards acetylene gas (C₂H₂), one of the most important arc discharge characteristic gases dissolved in oil-filled power equipments, were systematically measured. The ZnO nanowires based sensor exhibits excellent C₂H₂sensing behaviors than those of ZnO nanosheets, nanorods, and nanospheres, indicating a feasible way to develop high-performance C₂H₂gas sensor for practical application.