Efficient hydrogen sensor based on Ni-doped ZnO nanostructures by RF sputtering
TL;DR: In this paper, RF sputtered Ni-doped ZnO nanostructures for detection of extremely low concentration (1ppm) of hydrogen gas at moderate operating temperature of 75°C.
Abstract: We demonstrate RF sputtered Ni-doped ZnO nanostructures for detection of extremely low concentration (1 ppm) of hydrogen gas at moderate operating temperature of 75 °C. Structural, morphological, electrical and hydrogen sensing behavior of the Ni-doped ZnO nanostructures strongly depends on doping concentration. Ni doping exceptionally enhances the sensing response and reduces the operating temperature of the sensor as compared to undoped ZnO. The major role of the Ni-doping is to create more active sites for chemisorbed oxygen on the surface of sensor and, correspondingly, to improve the sensing response. The 4 at% of Ni-doped ZnO exhibits the highest response (∼69%) for 1% H 2 at 150 °C, which are ∼1.5 times higher than for the undoped ZnO. This is ascribed to lowest activation energy ∼6.47 KJ/mol. Diminishing of the relative response was observed in 6% Ni- doped ZnO due to separation of NiO phase.
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TL;DR: In this paper, the authors highlight the designs and mechanisms of different SMONs with various patterns (e.g., nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature.
Abstract: High-precision gas sensors operated at room temperature are attractive for various real-time gas monitoring applications, with advantages including low energy consumption, cost effectiveness and device miniaturization/flexibility. Studies on sensing materials, which play a key role in good gas sensing performance, are currently focused extensively on semiconducting metal oxide nanostructures (SMONs) used in the conventional resistance type gas sensors. This topical review highlights the designs and mechanisms of different SMONs with various patterns (e.g. nanoparticles, nanowires, nanosheets, nanorods, nanotubes, nanofilms, etc.) for gas sensors to detect various hazardous gases at room temperature. The key topics include (1) single phase SMONs including both n-type and p-type ones; (2) noble metal nanoparticle and metal ion modified SMONs; (3) composite oxides of SMONs; (4) composites of SMONs with carbon nanomaterials. Enhancement of the sensing performance of SMONs at room temperature can also be realized using a photo-activation effect such as ultraviolet light. SMON based mechanically flexible and wearable room temperature gas sensors are also discussed. Various mechanisms have been discussed for the enhanced sensing performance, which include redox reactions, heterojunction generation, formation of metal sulfides and the spillover effect. Finally, major challenges and prospects for the SMON based room temperature gas sensors are highlighted.
434 citations
TL;DR: In this paper, several techniques related to the synthesis of ZnO nanostructures and their efficient performance in sensing are reviewed, such as functionalization of noble metal nanoparticles, doping of metals, inclusion of carbonaceous nanomaterials, using nanocomposites of different MO x, UV activation, and post-treatment method of high-energy irradiation on ZnOs, with their possible sensing mechanisms.
323 citations
TL;DR: In this paper, an enhanced hydrogen-gas-sensing performance of a Ni-doped ZnO sensor decorated with the optimum concentration of reduced graphene oxide (rGO) was reported.
Abstract: We report enhanced hydrogen-gas-sensing performance of a Ni-doped ZnO sensor decorated with the optimum concentration of reduced graphene oxide (rGO). Ni-doped ZnO nanoplates were grown by radio frequency sputtering, rGO was synthesized by Hummer’s method and decorated by the drop cast method of various concentration of rGO (0–1.5 wt %). The current–voltage characteristics of the rGO-loaded sensor are highly influenced by the loading concentration of rGO, where current conduction decreases and sensor resistance increases as the rGO concentration is increased up to 0.75 wt % because of the formation of various Schottky heterojunctions at rGO/ZnO interfaces. With the combined effect of more active site availability and formation of various p–n heterojunctions due to the optimum loading concentration of rGO (0.75 wt %), the sensor shows the maximum sensing response of ∼63.8% for 100 ppm hydrogen at moderate operating temperature (150 °C). The rGO-loaded sensors were able to detect a minimum of 1 ppm hydrogen...
123 citations
TL;DR: In this paper, a 3D hierarchical porous MoS2 microspheres assembled by nanosheets were successfully fabricated via a facile yet efficient hydrothermal process using an assistance of CTAB as soft template which had significant effects on the final morphology of the final product.
94 citations
TL;DR: In this paper, the In2O3/ZnO sensor was tested with n-butanol as the probe analyte, and the results revealed that the response was 104.3 at a concentration of 100 ppm, 3.5 and 5.3 times higher than that of the pure ZnO and In 2O3 sensor, respectively.
Abstract: In2O3-nanoparticle-modified single crystalline ZnO nanorods with enhanced gas-sensing performance were prepared using a facile sol-gel and chemical precipitation process. In2O3 nanoparticles obtained good dispersibility and were modified on the surface ZnO nanorods. One-dimensional ZnO nanorods served as a matrix for In2O3 nanoparticles, which effectively restrained the agglomeration of the In2O3 nanoparticles and increased the active sites for the sensing reaction. The sensing performance of as-prepared In2O3/ZnO and ZnO sensors was systematically tested using n-butanol as the probe analyte. Test results revealed the In2O3/ZnO sensor response was 104.3 at a concentration of 100 ppm, 3.5 and 5.3 times higher than that of the pure ZnO and In2O3 sensor, respectively. The influence of added In2O3 on sensing performance of the In2O3/ZnO nanocomposites was discussed. Test results showed that the optimal atomic ratio of indium was 3.3%. The response of the In2O3/ZnO sensor reached 6.1 at a concentration of 1 ppm, suggesting good detection of n-butanol. The In2O3/ZnO sensor displayed rapid response-recovery speed along with good selectivity and stability. A possible sensing mechanism for In2O3/ZnO was thus proposed based on experimental data and band structure analysis.
74 citations
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TL;DR: A review of metal hydrides on properties including hydrogen-storage capacity, kinetics, cyclic behavior, toxicity, pressure and thermal response is presented in this article, where a group of Mg-based hydride stand as promising candidate for competitive hydrogen storage with reversible hydrogen capacity up to 7.6 W% for on-board applications.
2,890 citations
TL;DR: This paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.
Abstract: Sensing technology has been widely investigated and utilized for gas detection. Due to the different applicability and inherent limitations of different gas sensing technologies, researchers have been working on different scenarios with enhanced gas sensor calibration. This paper reviews the descriptions, evaluation, comparison and recent developments in existing gas sensing technologies. A classification of sensing technologies is given, based on the variation of electrical and other properties. Detailed introduction to sensing methods based on electrical variation is discussed through further classification according to sensing materials, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture absorbing materials. Methods based on other kinds of variations such as optical, calorimetric, acoustic and gas-chromatographic, are presented in a general way. Several suggestions related to future development are also discussed. Furthermore, this paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.
1,018 citations
TL;DR: In this article, the phase composition of the product and the gas-sensing properties were dependent on the preparation conditions (the presence of surfactant and the ratio of V ZnA c 2 ( 0.50 M ) / V NaOH ( 5.0 M ) ).
Abstract: ZnO sensors were fabricated from ZnO nanorods prepared by a hydrothermal method and their gas-sensing properties were investigated. It was found that the phase composition of the product and the gas-sensing properties were dependent on the preparation conditions (the presence of surfactant and the ratio of V ZnA c 2 ( 0.50 M ) / V NaOH ( 5.0 M ) ). The sensor prepared at a ratio of V ZnA c 2 ( 0.50 M ) / V NaOH ( 5.0 M ) = 1 without any surfactant exhibited the best performance, which was characterized by high response and good selectivity to low concentrations of H2S at room temperature. The sensor also had a high response, high selectivity and short response time to low concentrations of C2H5OH at 350 °C. These characteristics make the sensor to be a promising candidate for practical materials detecting low concentrations of H2S and C2H5OH. Especially, the response to 0.05 ppm H2S attained 1.7 at room temperature.
322 citations
TL;DR: In this paper, modern views on the reasons of time instability of gas sensors parameters, as well as approaches which could be used for the improvement of this important sensor's parameter, are summarized.
Abstract: In the present brief review modern views on the reasons of time instability of gas sensors parameters, as well as approaches, which could be used for the improvement of this important sensor's parameter, are summarized. In particular, the influence of factors such as structure transformation, phase transformation, poisoning, degradation of contacts and heaters, bulk diffusion, errors in design, change of humidity, fluctuations of temperature in the surrounding atmosphere, and interference effect was analyzed. It was shown that while designing devices such as solid-state gas sensors, there are no secondary issues or tasks—all are important. Sensors work in extreme temperatures in the presence of active gases, and therefore every element of the sensor could be responsible for its long-term stability. The conclusions, regarding the efficiency of approaches such as optimization of technological processes and optimization of exploitation processes used for improvement of stability of conductometric metal oxide gas sensors, were made as well.
270 citations
TL;DR: Graphene/Zinc oxide (ZnO) nanocomposite was prepared by in situ reduction of zinc acetate and graphene oxide (GO) during refluxing as mentioned in this paper.
Abstract: Graphene/zinc oxide (ZnO) nanocomposite was prepared by in situ reduction of zinc acetate ((CH3COO)2Zn·2H2O) and graphene oxide (GO) during refluxing. For the structural, morphological and elemental analysis, the synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FTIR). Hydrogen sensing properties of synthesized graphene/ZnO nanocomposite have been reported in this paper. For gas sensing properties, thick films of synthesized nanocomposite powder were fabricated on alumina substrate. Sensing results revealed that sensor based on 1.2 wt% graphene/ZnO composite exhibits best sensing response towards 200 ppm of hydrogen gas at an optimum operable temperature of 150 °C among the prepared samples with varying concentrations. Inclusion of graphene into ZnO significantly reduced the optimum operable temperature and increased the sensing response of graphene/ZnO composite towards hydrogen gas. Reported results are based on the change in electrical conductivity of synthesized nanocomposites due to superior electronic conductivity of graphene and the interaction between p-type graphene and n-type zinc oxide.
251 citations