Ppm CH4 Research Articles

High Selectivity MEMS C2H2 Sensor for Transformer Fault Characteristic Gas Detection**

AbstractAcetylene (C2H2), as an important characteristic gas in transformer fault diagnosis, should be accurately detected and effectively distinguished from other dissolved gases (H2, CH4, C2H6, C2H4, CO, CO2), which is crucial to determine whether the fault occurs and the fault type, but also faces challenges now. The rational design and employment of rare earth and noble metals are expected to address this issue. In this work, SnO2‐3 at% Sm2O3‐1 at% PdO based MEMS gas sensor was prepared to achieve high performance detection of C2H2 which has a response value of 56 to 50 ppm C2H2, response/recovery time of 2 s/136 s, lower detection limit of 1 ppm, power consumption of 15.5 mW, and weak cross sensitivity to other transformer fault characteristic gases. Lewis acids and bases theory was used to explain the reason why rare earth Sm is a benefit element to improve selectivity to C2H2. The formation of oxygen vacancies and hetero junctions was used to explain the increased sensitivity of the material. This study proved the feasibility of rare earth and noble metals as potential additives to enable advanced gas‐sensitive materials for highly selective transformer fault characteristic gas C2H2 detection.

UV-activated CH4 gas sensor based on Pd@Ni/ZnO microspheres

Developing methane (CH4) gas sensors with low working temperatures and high response has garnered substantial interest in reliably monitoring CH4 and achieving intrinsic safety. In this work, we combined photo-activation with bimetallic doping to explore CH4-sensing performance. ZnO, Pt/ZnO, and Pt@Ni/ZnO composites with different contents of Pt@Ni were synthesized. Their morphology, structure, and optical properties were characterized using various techniques. Subsequently, their CH4 sensing performance was systematically evaluated under ultraviolet (UV) illumination. The results show that the sensor based on 3Pt@Ni/ZnO composite demonstrated superior CH4 sensing performance among all sensors under UV illumination, presenting a low working temperature of 60 °C, a high response (904.04), which is approximately 60 times higher than pure ZnO (14.97) toward 5000 ppm CH4, and good response and recovery times of 4/174 s. The improved gas-sensing mechanism of the 3Pt@Ni/ZnO sensor was discussed and ascribed to the UV illumination, the synergistic effect of the bimetallic Pt@Ni, and the hollow structure of the ZnO. This study provides a promising gas-sensing material for CH4 detection at a low temperature assisted with UV illumination.

Self-driven sensing of acetylene powered by a triboelectric-electromagnetic hybrid generator

A hybrid generator consisting of the direct-current triboelectric nanogenerator (DC-TENG) based on the ternary dielectric triboelectrification effect and the electromagnetic generator (EMG) was designed to provide large output power even at low rotational speeds. At 120 rpm/min, the DC output of the hybrid generator realizes an open-circuit voltage of 3940 V and a short-circuit current of 8 mA, which is capable of powering 1288 light-emitting diodes (LEDs) and a temperature and humidity meter. A ZnO/MXene nanocomposite acetylene sensor has been developed, which can detect trace amounts of acetylene at room temperature. It has a response/recovery speed of 14 s/6 s, a high response of 178%, and long-term stability of more than 30 days for 5 ppm C2H2. In addition, the sensor is highly selective for acetylene, outperforming other gases by more than 100% for the seven characteristic gases in transformer oil. The hybrid generator powered acetylene sensing system was realized to detect the acetylene concentration at room temperature with an excellent response capability, short response recovery time (14 s/9 s), and good linearity and sensitivity.

Highly selective methane sensing based on enhanced dual sieving effects by ZnO/Pd@Co node-replaced ZIF-8 nanorods

Highly selective methane sensing remains a formidable challenge in the field of metal oxide semiconductor (MOS)-based gas sensors. To address this issue, zeolitic imidazolate framework (ZIF) modulation is considered as an effective approach because of its pore size sieving and polarity sieving effects. In this work, core-shell ZnO/Pd@Co node-replaced ZIF-8 (ZIF-8/67) nanorods were synthesized by self-sacrificial template method, followed by post-synthetic modification of ZIF-8. When the replacement ratio of Co nodes reached 12.4%, ZnO/Pd@ZIF-8/67 exhibited a response of 12.2% to 500 ppm CH4 at 210°C but no response to 50 ppm CO, 50 ppm NH3 and 5 ppm NO2, showing excellent selectivity. By limiting rotational freedom of 2-methylimidazole, Co node replacement decreased the effective pore size from 4.0 to 4.2 Å to 3.8–4.0 Å and hindered the diffusion of NO2 with the dynamic diameter of 4.5 Å, thus enhancing the pore size sieving effect. Moreover, polarity sieving effect is also enhanced due to the favourable adsorption of polar CO (3.76 Å) and NH3 (2.6 Å) by ZIF. Therefore, the selectivity of nonpolar CH4 (3.8 Å) was improved. This work provides a new strategy for reasonably controlling and modulating the ZIF structure to achieve high selectivity in MOS-based sensors.

NiO/ZnO heterojunction microspheres for methane detection at room temperature

Low working temperature CH4 gas sensors are necessary to explore to obtain intrinsic safety. In this work, NiO/ZnO microspheres were synthesized through facile hydrothermal methods and the strategy of photo-activation was used to develop room-temperature CH4 gas sensors. The characterizations of as-prepared samples were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence spectra, and electrochemical impedance spectroscopy. The results indicated that NiO/ZnO is a microsphere structure assembled with porous nanosheets. NiO/ZnO composite had good optical properties to use light energy. The methane gas-sensing performances were systematically investigated at room temperature. It shows that the prepared sensors exhibit good CH4 gas sensing performances at room temperature under UV illumination. NiO/ZnO microspheres exhibited enhanced response values. In particular, NiO/ZnO-2 sensor exhibited the highest response (8.61–5000 ppm CH4), which is 3.42 times of pure ZnO, low detection limit, good selectivity, and repeatability under UV light. The excellent gas sensing performances may be related to the UV light and the formation of heterojunction, which widens the depletion layer and increases the amount of valid carriers. This work gives a sight to explore photo-activated CH4 gas sensors.

Double-channel sensors for high precision measurement of methane based on a dual-path Herriott cell.

A double-channel methane (CH4) sensor was developed using a dual-pass multipass cell (DP-MPC) and a novel method that combines averaging dual-channel concentration signals with optimized detector gain configuration. This DP-MPC features two input/output coupling holes, resulting in absorption path lengths of approximately 95.8 m and 35.8 m, respectively. By optimizing the photodetector gain configuration and averaging the dual-channel concentration signals, the detection performance of the sensor was further enhanced. Allan deviation analysis indicated that after optimizing the detector gain, the measurement precision after dual-channel averaging reaches 21 ppb with an integration time of 1 s at a concentration of 2 ppm CH4, which is approximately 1.4 times higher than the measurement precision of the long-path channel (31 ppb) and short-path channel (30 ppb). The time required to achieve a measurement precision of 21 ppb is 2.4 s for the long-path channel and 2.1 s for the short-path channel. The response speed of the dual-channel averaging is approximately 2 times that of any single channel. Meanwhile, the sensor demonstrated its stability and reliability through continuous outdoor atmospheric CH4 measurements.

Investigation into the enhanced gas sensing performance for CH4: Comparative study of MOF-derived and traditionally synthesized ZnCo2O4 flower based composite

Detecting very sensitive and selective methane (CH4) gas is very challenging and a major task in real-world situations. Herein, this work demonstrates a comparative analysis on the sensing performance between MOF-derived and conventionally prepared spinel-based nanocomposite for CH4 gas. Initially, ZnCo2O4 flower shaped spinel was synthesized via solvothermal route using ZIF-67 as template as well as conventional method using SDS. Both the ZnCo2O4 flower structure contains a lot of voids, making it easy for gases to diffuse while also allows a lot of sites for gas adsorption. Keeping an eye on this, a detailed study on the role of such factors for sensing performance of the sensor was presented utilizing both normally synthesized and MOF-derived rGO-ZnCo2O4 sensor. Interestingly, MOF-derived ZnCo2O4 flower has shown significantly higher response (S% = 3.2%) at 150 °C towards 100 ppm of CH4 as compare to conventionally prepared ZnCo2O4 flower (S% = 2.5%). Later on, the sensing ability of the designed 3DGO/MOF-derived ZnCo2O4 flower composite towards CH4 gas was also investigated carefully. The designed sensor exhibited a high response (5.1%) towards 100 ppm CH4 at room temperature with low response/recovery time (14 s/20 s) because of the presence of more number of oxygen defects in the composite (51.32%)

MOF-derived Co3O4 nanoparticles over direct grown ZnO nanoflower on ceramic for CO sensor with high selectivity

ZnO nanoflower was directly fabricated on ceramic and then Co3O4 was grown in-situ on ZnO nanoflower by a MOF-derived method. Co3O4 nanoparticles were successfully coated on the surface of ZnO nanoflower to develop a sensor for the detection of carbon monoxide. Notably, the Co3O4/ZnO sensor exhibits an outstanding response of 38 % to 100 ppm CO at 210 ℃ with a fast response/recovery time (38 s/50 s). In addition, the sensor showed excellent selectivity for CO, which is 14 times better than for the second gas (500 ppm CO and NH3). In the meantime, the sensor's response remained a stable value when the 100 ppm CO is mixed with 100 ppm H2, CH4 and HN3, respectively. The prominent CO sensing performance of the sensor is attributed to its unique structure charaterastics of nanoflower and the constructed heterostructure, which provides a large surface area and abundant active sites. Therefore, the sensor based on MOF-derived Co3O4 nanoparticles directly on ZnO nanoflower have promising application for constructing high performance CO sensor in the detection domain.

Carburization and tensile behavior of Alloy 617 in impure helium containing a part-per-million level of CH4 at 950 °C

The carburization and tensile behavior of Alloy 617 corroded at 950 °C for 100 h in the impure helium containing methane were investigated. In helium containing 20 ppm CH4, Alloy 617 exhibited slight carburization and held its plasticity. However, in helium containing 200 ppm CH4, Alloy 617 was carburized to a depth of over 20 % and lost plasticity. In addition, the stress-strain curves in the plastic phase at room temperature exhibited a serrated flow phenomenon in both two environments, primarily caused by dynamic interactions between carbide-induced crack pinning and stress-concentration-induced crack unpinning.

Inhibiting effect of C3H6 on the performance of Cu-SSZ-13 catalysts for NH3 selective catalytic reduction

Hydrocarbons (HCs) have been found to be a potential source of catalyst poisoning in ammonia selective catalytic reduction (NH3-SCR) of NOx. As one of the predominant constituents of hydrocarbons, propene (C3H6) was selected to investigate its inhibitory effect on Cu-SSZ-13 catalysts utilized in the NH3-SCR reaction. The results of standard SCR tests mixing C3H6 and NH3 showed that the NH3-SCR activity of Cu-SSZ-13 catalysts was inhibited in the range of 150–650 °C with the introduction of C3H6 and the NOx conversion was lowest in the presence of 2000 ppm C3H6. The competitive adsorption and NH3 oxidation activity were extensively studied. It was found that NH3 and C3H6 could both be stored on Brønsted acid sites and Cu sites. The introduction of C3H6 during NH3-TPD experiments caused an increase of weakly adsorbed NH3 on the weak Lewis acid sites and a decrease of adsorbed NH3 on the strong Lewis acid sites and Brønsted acid sites, confirming the existence of the competitive adsorption between NH3 and C3H6. Based on TPO experiments, C3H6 enhanced the NH3 oxidation activities in the temperature range of 250–650 °C, and coke deposition might be generated on the catalysts, causing the decline of NOx conversion during NH3-SCR with C3H6.

Annealing effect on the methane sensing performance of Pt–SnO2/ZnO double layer sensor

Low power consumption is a new emerged requirement for methane sensors long-term working in a gas supervisorycontrolsystem. Great challenges remain in development of heat free methane sensors based on metal oxide semiconductors (MOS). In this work, Pt-doped SnO2 (Pt-SnO2) grow on well aligned ZnO nanorod-array to form an inter-staggered double-layer structure on AZO glass by a two-step hydrothermal method, with the annealing temperature being systematically studied. The optimized processing parameters are 1 at% Pt doping content and 700 °C annealing temperature, offering the best sensing response of 3.36 to 800 ppm CH4 at room temperature. SnO2/ZnO without Pt doping shows linear I-V relationship, while the Pt-SnO2/ZnO shows a Schottky-like I-V curve with the Schottky barrier height decreases as increasing the CH4 concentration. The activation energy (ΔEa) for CH4 dissociation decreases with increasing the annealing temperature, and the ΔEa of the optimized Pt-SnO2/ZnO sample is only one-third of that in the SnO2/ZnO. In addition to the piezoelectric polarization electric field in ZnO, the build up Schottky-like barrier and the reduced activation energy via Pt doping and annealing are demonstrated to be efficient for enhancing the methane sensing performance at low operation temperature.

Massive enhancement in sensitivity of mixed potential sensors towards methane and natural gas through magnesia stabilized zirconia low ionic conductivity substrate

Monitoring of methane leaks from natural gas (NG) sources during production and transport is vital to combating the threat of greenhouse gases to the global climate. An additive manufacturing route was developed for the printing of a CTE matched, low reactivity and low ionic conductivity magnesia stabilized zirconia (MSZ) substrate for production of a four-electrode (indium tin oxide, lanthanum strontium chromite, and Au sensing electrodes measured against a Pt negative electrode) same-side planar mixed potential electrochemical sensor (MPES) with porous 3 mol% YSZ as electrolyte. The MSZ substrate based MPES achieves a 40 ppm limit of detection for methane in a simulated natural gas mix. Additionally, a 20 times enhanced response in the ITO vs. Pt signal over sensors using yttria-stabilized zirconia (YSZ) substrates at 100 ppm CH4 in simulated natural gas is observed. This research illustrates the importance of a CTE matched, low reactivity, low conductivity substrate for optimal performance of same-side planar MPES devices for NG leak detection while allowing for application of high temperature co-fired ceramic technologies.

Ultra-Stable Temperature Controller-Based Laser Wavelength Locking for Improvement in WMS Methane Detection.

In the wavelength modulation spectroscopy (WMS) gas detection system, the laser diode is usually stabilized at a constant temperature and driven by current injection. So, a high-precision temperature controller is indispensable in every WMS system. To eliminate wavelength drift influence and improve detection sensitivity and response speed, laser wavelength sometimes needs to be locked at the gas absorption center. In this study, we develop a temperature controller to an ultra-high stability level of 0.0005 °C, based on which a new laser wavelength locking strategy is proposed to successfully lock the laser wavelength at a CH4 absorption center of 1653.72 nm with a fluctuation of fewer than 19.7 MHz. For 500 ppm CH4 sample detection, the 1σ SNR is increased from 71.2 dB to 80.5 dB and the peak-to-peak uncertainty is improved from 1.95 ppm down to 0.17 ppm with the help of a locked laser wavelength. In addition, the wavelength-locked WMS also has the absolute advantage of fast response over a conventional wavelength-scanned WMS system.

Investigation of hot spring gas components and soil gas fluxes in Arxan Holocene volcanic field, Inner Mongolia, NE China

The latest research results show that there is a unified magma system and heating channel beneath the Arxan volcanic field, indicating a potential risk of eruption. The Arxan volcanic field features multiple gas emission sites (e.g., Jinjianggou hot springs and Yinjianggou hot springs) and exhibits strong hydrothermal activity. In this study, measurements of the hot spring gas composition and soil CO2 flux in the Arxan Holocene volcanic field were conducted, and the results were combined with previous research results to analyze the degassing characteristics of this region. The results show that the volcanic gases in the Arxan volcanic field are composed of 0.07%–1.09% CO2, 0.33–12 ppm CH4, 1.57–53 ppm H2, 800–30,241 ppm He, and 1.14%–1.86% Ar. The He content in this area is notably higher than that in other dormant volcanoes in China. This difference is possibly caused by U–Th decay in the Mesozoic granodiorite and acidic volcanic rocks in the study area, which can produce substantial radiogenic He. The soil gas concentrations near the Jinjianggou and Yinjianggou hot springs are higher than those of two Holocene volcanoes. The peak CO2 concentration in the soil near the Jinjianggou hot spring can reach 35,161 ppm. The single-site soil microseepage CO2 flux in the Arxan volcanic field is 4.66–107.18 g m−2 d−1, and the estimated annual CO2 emission flux from the volcanic field to the atmosphere is 0.63 × 105 t, which also demonstrates that soil CO2 flux of Arxan volcano is comparable to the soil CO2 emission level of the Iwojima volcano.

Remarkably Enhanced Methane Sensing Performance at Room Temperature via Constructing a Self‐Assembled Mulberry‐Like ZnO/SnO2 Hierarchical Structure

Development of metal oxide semiconductors‐based methane sensors with good response and low power consumption is one of the major challenges to realize the real‐time monitoring of methane leakage. In this work, a self‐assembled mulberry‐like ZnO/SnO2 hierarchical structure is constructed by a two‐step hydrothermal method. The resultant sensor works at room temperature with excellent response of ~56.1% to 2000 ppm CH4 at 55% relative humidity. It is found that the strain induced at the ZnO/SnO2 interface greatly enhances the piezoelectric polarization on the ZnO surface and that the band bending results in the accumulation of chemically adsorbed ions close to the interface, leading to significant improvement in the sensing performance of the methane gas sensor at room temperature.

Enhanced CH4 sensing performances of g-C3N4 modified ZnO nanospheres sensors under visible-light irradiation

High operating temperature, low response as well as insufficient stability are still enormous challenges faced by MOS methane sensors in practical application. An effective strategy to address these drawbacks is to use light irradiation, but the activation response of sensors operating at room temperature is unsatisfactory. Therefore, we developed an artful precipitation-calcination strategy to fabricate a series of g-C3N4 modified ZnO composites and investigated light-activated methane-sensing performance at room temperature. The material characterization results indicated that ZnO nanospheres with porous nanosheet structures were attached to the tulle-like g-C3N4 surface and the modification of g-C3N4 enhanced the light absorption ability of ZnO in the visible region, with the wavelength range of 400–520 nm. Noticeably, ZnO/g-C3N4–5 wt% (ZC-5 wt%) sensor exhibited superior sensing performance to 1000 ppm CH4 under visible light irradiation, with a response value of 6.891. The improved methane-sensing properties are most likely due to visible light irradiation and the heterojunction interface formed between the composites. Last but not least, the sensor presented excellent repeatability and stability, which will hold broad application prospects in the detection of methane.

Electrosynthesis of polymer-grade ethylene via acetylene semihydrogenation over undercoordinated Cu nanodots

The removal of acetylene impurities remains important yet challenging to the ethylene downstream industry. Current thermocatalytic semihydrogenation processes require high temperature and excess hydrogen to guarantee complete acetylene conversion. For this reason, renewable electricity-based electrocatalytic semihydrogenation of acetylene over Cu-based catalysts is an attractive route compared to the energy-intensive thermocatalytic processes. However, active Cu electrocatalysts still face competition from side reactions and often require high overpotentials. Here, we present an undercoordinated Cu nanodots catalyst with an onset potential of −0.15 V versus reversible hydrogen electrode that can exclusively convert C2H2 to C2H4 with a maximum Faradaic efficiency of ~95.9% and high intrinsic activity in excess of −450 mA cm−2 under pure C2H2 flow. Subsequently, we successfully demonstrate simulated crude ethylene purification, continuously producing polymer-grade C2H4 with <1 ppm C2H2 for 130 h at a space velocity of 1.35 × 105 ml gcat−1 h−1. Theoretical calculations and in situ spectroscopies reveal a lower energy barrier for acetylene semihydrogenation over undercoordinated Cu sites than nondefective Cu surface, resulting in the excellent C2H2-to-C2H4 catalytic activity of Cu nanodots.

Photoacoustic spectrometry and resonant frequency tracking based dual-mode gas sensor

Photoacoustic spectrometry has excellent advantages in trace gas detection. However, due to the influence of gas saturation absorption, when the gas concentration spikes to a certain level, this technology is difficult to achieve accurate detection. Therefore, a dual-mode gas sensor based on photoacoustic spectroscopy and resonant frequency tracking is developed by the features of both detection technologies. A tunable DFB diode laser in the 1654 nm wavelength range and a loudspeaker are used for the photoacoustic detection, and the resonant frequency tracking, respectively. A resonant photoacoustic cell is used as the sensing element to work in dual-mode by time-division multiplexing technology. The wavelength-modulated photoacoustic detection is enabled in the methane concentration below 30%. When the gas concentration exceeds 30%, it will be automatically switched to the measurement-mode of resonant frequency tracking by the fast Fourier transform. The double-range gas detection is realized by a single sensor with dual-mode detecting functionality. With the wavelength modulation and lock-in harmonic detection method, the minimum detectable limit (1σ) of 3.5 ppm CH4 was demonstrated under the photoacoustic detection mode. The response time of the sensor is about 10 s within the measurement range of double-range.

High precision and sensitivity detection of gas measurement by laser wavelength modulation spectroscopy implementing an optical fringe noise suppression method

In this work, a novel method to suppress optical fringe noise in the tunable diode laser absorption spectroscopy is proposed and applied to the CH4 gas sensor perturbed by optical fringes for higher detection precision and sensitivity. For the 2nd harmonic(2f) signal of 20 ppm CH4 spoiled by optical fringes and random noise, by the novel method, the signal-to-noise ratio (SNR) of the 2f signal is improved about 6.5 times from 17 to 182 with an optimal averaging spectral range Δλ. A ∼1.5 times improvement in the measurement precision of CH4 is achieved compared to unprocessed raw signal. The corresponding minimum detectable concentration can be improved from 3 ppb down to 0.78 ppb. The corresponding noise equivalent absorption sensitivity (NNEA) and the noise equivalent concentration (NEC) of the system is 6.13×10−11 cm−1 W Hz−1/2 and 0.181 ppm, respectively.

Surprising Tribo‐catalytic Conversion of H2O and CO2 into Flammable Gases utilizing Frictions of Copper in Water

AbstractCopper rotary disks were fabricated through mounting copper disks and magnets on opposite surfaces of Teflon disks separately, and quartz glass reactors (150 mL) were modified through covering their bottoms with Al2O3, copper, and titanium disks separately. For a glass‐bottomed reactor placed with a copper rotary disk and filled with 50 mL water and 1 atm CO2, flammable gases of 670.96 ppm H2, 22.21 ppm CO, 3.98 ppm CH4, 0.96 ppm C2H4, and 0.66 ppm C2H6 were surprisingly produced after the copper rotary disk was driven to rotate for 5 h; flammable gases were obtained in comparable amounts for reactors with Al2O3, copper, and titanium bottoms separately. A tribo‐catalytic mechanism has been proposed, in which water at micro‐holes in friction surfaces is squeezed by elastically deformed copper of rotating copper disks, and under increased pressure CO2 and H2O are catalyzed to react to form flammable gases by copper.