Highly sensitive H2 gas sensor of Co doped ZnO nanostructures
10 Apr 2018-Vol. 1942, Iss: 1, pp 050059
TL;DR: In this paper, the hydrogen gas sensing properties based on Co doped ZnO nanostructures are explored, and the maximum relative response was occurred by the 2.5% Co-doped sensors among undoped and other doped sensors.
Abstract: In this report, the hydrogen gas sensing properties based on Co doped ZnO nanostructures are explored. The undoped and Co doped nanostructures were grown by RF magnetron sputtering system, and its structural, morphological, and hydrogen sensing behavior are investigated. The maximum relative response was occurred by the 2.5% Co doped ZnO nanostructures among undoped and other doped sensors. The enhancement of relative response might be due to large chemisorbed sites formation on the ZnO surface for the reaction to hydrogen gas.
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TL;DR: In this paper, a hierarchical bi-layered inverse opaline film was constructed with a ZnO sensing layer stacked with an Au electrode for impressive H2 sensing activities, where both morphological and crystallographic properties were optimized using KCl as the porogen.
Abstract: Three-dimensionally ordered macro/mesoporous materials are known to possess a large accessible surface area with impressive permeability. In this work, we combine electrophoresis and electrodeposition to fabricate a hierarchical bi-layered inverse opaline film in which a ZnO sensing layer is stacked with an Au electrode for impressive H2 sensing activities. To enhance its responsiveness, both morphological and crystallographic properties of ZnO inverse opals are optimized using KCl as the porogen. The resulting ZnO inverse opals demonstrate a specific surface area that is three times larger over comparable ZnO inverse opals by the formation of nanoporous skeletons. In addition, the deposition bath was deliberately designed so the predominant crystallographic plane of ZnO is shifted from (10 1 - 0) to (0001) as the latter exhibits superior activity toward reducing gases. Through X-ray photoelectron spectroscopy, we show a significant increase of chemisorbed oxygen on the (0001) plane. Consequently, our hierarchical bi-layered inverse opals reveal a 500 % improvement in the sensitivity toward 15 ppm H2 under 200 °C. In short, this is the first demonstration of a vertically-arranged inverse opaline film incorporating both metal and oxide layers to function as an integrated three-dimensional gas sensor with low detection limit.
22 citations
TL;DR: In this paper, a review of the recent advances in doped ZnO for CO sensing applications is presented, which includes room-temperature gas sensing, and some perspectives for future investigations in the context of advancements in CO sensing using doped znO2.
Abstract: Monitoring and detecting carbon monoxide (CO) are critical because this gas is toxic and harmful to the ecosystem. In this respect, designing high-performance gas sensors for CO detection is necessary. Zinc oxide-based materials are promising for use as CO sensors, owing to their good sensing response, electrical performance, cost-effectiveness, long-term stability, low power consumption, ease of manufacturing, chemical stability, and non-toxicity. Nevertheless, further progress in gas sensing requires improving the selectivity and sensitivity, and lowering the operating temperature. Recently, different strategies have been implemented to improve the sensitivity and selectivity of ZnO to CO, highlighting the doping of ZnO. Many studies concluded that doped ZnO demonstrates better sensing properties than those of undoped ZnO in detecting CO. Therefore, in this review, we analyze and discuss, in detail, the recent advances in doped ZnO for CO sensing applications. First, experimental studies on ZnO doped with transition metals, boron group elements, and alkaline earth metals as CO sensors are comprehensively reviewed. We then focused on analyzing theoretical and combined experimental-theoretical studies. Finally, we present the conclusions and some perspectives for future investigations in the context of advancements in CO sensing using doped ZnO, which include room-temperature gas sensing.
15 citations
References
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TL;DR: In this article, the current industrial uses of hydrogen in various industries in the industrial world will be summarized and discussed in more detail, including the use of hydrogen as a fuel in space applications, as an O2 scavenger in heat treating of metals and for its low viscosity and density.
511 citations
TL;DR: Aligned zinc oxide nanorods were synthesized directly via a two-step solution approach on an Al2O3 tube, and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) as mentioned in this paper.
Abstract: Aligned zinc oxide nanorods were synthesized directly via a two-step solution approach on an Al2O3 tube, and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The zinc oxide nanorods prepared were uniform with diameters of 10–30 nm and lengths about 1.4 μm. The response Sr (= Ra/Rg) of the aligned zinc oxide nanorod sensor reached 18.29 and 10.41 to 100 ppm ethanol and hydrogen, respectively, which was a two-fold increase compared with that reported in literature, demonstrating the potential for developing stable and sensitive gas sensors.
317 citations
TL;DR: In this article, Lanthanum (La) doped ZnO nanofibers with bead-like structures were facilely produced by electrospinning technique, which can be used as a promising material for acetone sensors.
Abstract: In this work, Lanthanum (La) doped ZnO nanofibers with bead-like structures were facilely produced by electrospinning technique. The obtained La-doped ZnO products were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show that La doping changes the structures of ZnO nanofibers markedly. La-doped ZnO nanofibers have unique bead-like nanostructures, in which two phases of hexagonal La2O3 and wurtzite ZnO coexist along with partially incorporation of La into ZnO lattice. The gas sensing performances of the La-doped ZnO nanostructures to acetone were investigated via static gas sensor testing system. The sensing test results indicate that an appropriate amount of La doping greatly improves the gas sensing properties of ZnO nanofibers. The 1.0 wt% La-doped ZnO sensor has the highest selectivity and response (64, to 200 ppm acetone at 340 °C), in addition to its short response time and recovery time. The unique bead-like structure and the gas sensing mechanism of La-doped ZnO nanofibers are discussed. The La-doped ZnO nanostructures we have produced can be used as a promising material for acetone sensors.
106 citations
TL;DR: In this paper, Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150°C and the morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy.
Abstract: Ni-doped zinc oxide (ZnO) nanorods had been successfully fabricated via a fast microwave-assisted hydrothermal synthesis at 150 °C. The morphology and composition were carefully characterized by X-ray diffraction, field emission scanning electronic microscopy, and transmission electron microscopy. Gas-sensing testing results demonstrated that Ni-doped ZnO nanorods had enhanced gas-sensing performance. Furthermore, AC impedance spectroscopy and DC current–voltage curves were observed to investigate the gas-sensing mechanism. Current–voltage curves are approximately close to a linear function, indicating the potential barriers formed at the electron-depleted surface layer occupy a dominant when carriers transport in the gas sensor, and AC impedance spectra indicates the potential barriers height of the electron-depleted surface layer.
75 citations
TL;DR: In this paper, a mechanism for the enhanced H 2 response of Co:ZnO is proposed that involves donor-related oxygen vacancies (V O ) introduced by the Co dopants in the ZnO lattice.
Abstract: We report here excellent H 2 gas response property of Co-doped ZnO nanorods (Co:ZnO NRs). Co:ZnO NRs have been synthesized by hydrothermal method by varying the Co content from 0 to 10 mol%. It is found that Co:ZnO NRs with 8 mol% of Co exhibits the highest and faster H 2 gas response ability compared to the undoped ZnO resulting in a ∼5 fold enhancement in the gas response in the presence of air at 150 °C. While the gas response value (S (%) = [(I g -I a )/I a ] × 100, where I a is the current of the sensors in the presence of air only and I g is the current in the presence of certain H 2 concentration) to 3000 ppm H 2 for undoped ZnO NRs’sensor is 11%, an unprecedented high value of 53.7% is obtained for the Co:ZnO with 8 mol% of Co. Based on the electrical current and photoluminescence results, a mechanism for the enhanced H 2 response of Co:ZnO is proposed that involves donor-related oxygen vacancies (V O ) introduced by the Co dopants in the ZnO lattice.
72 citations