Hydrogen Gas Sensor Research Articles

Structure-dependent room-temperature hydrogen sensing of Nb2O5 nanorods prepared by topological transformation process

The development of reliable low-power-consumption hydrogen gas sensors is of great significance for the accurate detection of hydrogen leakage in the hydrogen-related industries. Nb2O5 nanomaterials have exhibited great potential for building highly selective hydrogen sensors owing to its outstanding hydrogen catalytic capability, but still suffer from relatively low hydrogen sensitivity at room temperature. Herein, the orthorhombic and hexagonal Nb2O5 nanorods with different defect states are prepared through a combined topological transformation process. The Nb2O5 nanorods with polycrystalline orthorhombic structures exhibit much higher room-temperature hydrogen response comparing with the single-crystalline hexagonal Nb2O5 nanorods. Moreover, both phases of the Nb2O5 nanorods exhibit certain amounts of oxygen vacancies, as well as the interstitial Nb4+ and related oxygen defects. The elimination of the Nb4+ and related oxygen defects can significantly enhance the surface reactivity of the Nb2O5 nanorods and improve the sensor response of the chemiresistor devices. The sensor based on the defect-modified orthorhombic Nb2O5 nanorods shows sensitive and highly selective room-temperature hydrogen sensing performance with the detection limit of 160 ppm. The structure-dependent hydrogen sensing behavior of the Nb2O5 nanorods can be attributed to the redox reaction between hydrogen and pre-adsorbed oxygens, which can be promoted by the superior gas adsorption and pathway effect of the orthorhombic Nb2O5 lattice.

CdS/TiO2 nano hybrid heterostructured materials for superior hydrogen production and gas sensor applications

In efforts to minimize environmental pollution and carbon-based gas emissions, photocatalytic hydrogen production and sensing applications at ambient temperature are important. This research reports on the development of new 0D/1D materials based on TiO2 nanoparticles grown onto CdS hetersturctured nanorods via two-stage facile synthesis. The titanate nanoparticles when loaded onto CdS surfaces at an optimized concentration (20 mM), exhibited superior photocatalytic hydrogen production (21.4 mmol/h/gcat). The optimized nanohybrid was recycled for 6 cycles up to 4 h, indicating its excellent stabity for a prolonged period. Also, the photoelectrochemical water oxidation in alkaline medium was investigated to offer the optimized CRT-2 composite with 1.91 mA/cm2@0.8 V vs. RHE (0 V vs. Ag/AgCl) that was used for effective room-temperature NO2 gas detection exhibiting a higher response (69.16%) to NO2 (100 ppm) at room temperature at the lowest detection limit of ∼118 ppb than the pristine counterparts. Further, NO2 gas sensing performance of CRT-2 sensor was increased using UV light (365 nm) activation energy. Under the UV light, the sensor exhibited a remarkable gas sensing response quick response/recovery times (68/74), excellent long-term cycling stability, and significant selectivity to NO2 gas. Due to high porosity and surface area values of CdS (5.3), TiO2 (35.5), and CRT-2 (71.5 m2/g), excellent photocatalytic H2 production and gas sensing of CRT-2 is ascribed to morphology, synergistic effect, improved charge generation, and separation. Overall, 1D/0D CdS@TiO2 is proved to be an efficient material for hydrogen production and gas detection.

Polymer Ring-Flexure-Membrane Suspended Gate FET Gas Sensor: Design, Modelling and Simulation.

This work reports the design, modelling, and simulation of a novel polymer MEMS gas sensor platform called a ring-flexure-membrane (RFM) suspended gate field effect transistor (SGFET). The sensor consists of a suspended polymer (SU-8) MEMS based RFM structure holding the gate of the SGFET with the gas sensing layer on top of the outer ring. During gas adsorption, the polymer ring-flexure-membrane architecture ensures a constant gate capacitance change throughout the gate area of the SGFET. This leads to efficient transduction of the gas adsorption-induced nanomechanical motion input to the change in the output current of the SGFET, thus improving the sensitivity. The sensor performance has been evaluated for sensing hydrogen gas using the finite element method (FEM) and TCAD simulation tools. The MEMS design and simulation of the RFM structure is carried out using CoventorWare 10.3, and the design, modelling, and simulation of the SGFET array is carried out using the Synopsis Sentaurus TCAD. A differential amplifier circuit using RFM-SGFET is designed and simulated in Cadence Virtuoso using the lookup table (LUT) of the RFM-SGFET. The differential amplifier exhibits a sensitivity of 2.8 mV/MPa for a gate bias of 3 V and a maximum detection range of up to 1% hydrogen gas concentration. This work also presents a detailed fabrication process integration plan to realize the RFM-SGFET sensor using a tailored self-aligned CMOS process adopting the surface micromachining process.

Hydrogen Gas Sensing Properties of Mixed Copper-Titanium Oxide Thin Films.

Hydrogen is an efficient source of clean and environmentally friendly energy. However, because it is explosive at concentrations higher than 4%, safety issues are a great concern. As its applications are extended, the need for the production of reliable monitoring systems is urgent. In this work, mixed copper-titanium oxide ((CuTi)Ox) thin films with various copper concentrations (0-100 at.%), deposited by magnetron sputtering and annealed at 473 K, were investigated as a prospective hydrogen gas sensing material. Scanning electron microscopy was applied to determine the morphology of the thin films. Their structure and chemical composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The prepared films were nanocrystalline mixtures of metallic copper, cuprous oxide, and titanium anatase in the bulk, whereas at the surface only cupric oxide was found. In comparison to the literature, the (CuTi)Ox thin films already showed a sensor response to hydrogen at a relatively low operating temperature of 473 K without using any extra catalyst. The best sensor response and sensitivity to hydrogen gas were found in the mixed copper-titanium oxides containing similar atomic concentrations of both metals, i.e., 41/59 and 56/44 of Cu/Ti. Most probably, this effect is related to their similar morphology and to the simultaneous presence of Cu and Cu2O crystals in these mixed oxide films. In particular, the studies of surface oxidation state revealed that it was the same for all annealed films and consisted only of CuO. However, in view of their crystalline structure, they consisted of Cu and Cu2O nanocrystals in the thin film volume.

Investigation of palladium gated polarity controllable FET as a highly sensitive and robust hydrogen gas sensor

AbstractThe paper investigates the design and performance of a novel palladium gated‐polarity controllable Field Effect Transistor (FET) (PC‐FET) for hydrogen gas sensing applications. In the present work, catalytic sensing metal gate (palladium) is chosen as control gate (CG) and hydrogen gas molecules are exposed on the region controlled by CG. A compact analytical model has been derived for PC‐FET based sensor and the performance of the proposed gas sensor has been examined in terms of energy band profile, surface potential, electric field, transfer characteristics and transconductance and the derived analytical results are verified using TCAD simulated results. Furthermore, the sensitivity metrics such as threshold voltage sensitivity, drain current sensitivity, transconductance sensitivity and ION/OFF sensitivity have also been extensively investigated for both modes of proposed sensor for a wide range of pressure that is, 10−14–10−8 Torr.

Production of hydrogen gas sensors based on sol–gel spin-coated Nb2O5 thin films

Production of hydrogen gas sensors based on sol–gel spin-coated Nb2O5 thin films

Gas sensing properties of mixtures of copper and titanium oxides thin films

The subject of the current studies were mixtures of copper and titanium oxide thin films,with various elemental compositions, deposited by magnetron sputtering and annealed in the postprocess.The effect of elemental composition and annealing temperature on the morphology of thinfilms was determined using scanning electron microscope images. The crystal structure and chemicalcomposition of copper‒titanium oxide (CuTi)Ox mixtures were investigated by X-ray diffraction.Hydrogen gas sensing experiments were performed for hydrogen with concentrations ranging from 100to 1,000 ppm. The resistance of the prepared (CuTi)Ox mixtures increased during hydrogen exposure,demonstrating the applicability of these oxides in hydrogen sensing. In addition, better sensor responseswere obtained for the mixtures in comparison to single copper oxides or titanium oxides. Mixturesof copper oxides and titanium oxides may be promising materials for hydrogen sensor applications.Keywords: mixtures of copper and titanium oxides, hydrogen gas sensors, mixed copper and titaniumoxides, thin films, magnetron sputtering

High Selectivity Hydrogen Gas Sensor Based on WO3/Pd-AlGaN/GaN HEMTs

We investigated the hydrogen gas sensors based on AlGaN/GaN high electron mobility transistors (HEMTs) for high temperature sensing operation. The gate area of the sensor was functionalized using a 10 nm Pd catalyst layer for hydrogen gas sensing. A thin WO3 layer was deposited on top of the Pd layer to enhance the sensor selectivity toward hydrogen gas. At 200 °C, the sensor exhibited high sensitivity of 658% toward 4%-H2, while exhibiting only a little interaction with NO2, CH4, CO2, NH3, and H2S. From 150 °C to 250 °C, the 10 ppm hydrogen response of the sensor was at least eight times larger than other target gases. These results showed that this sensor is suitable for H2 detection in a complex gas environment at a high temperature.

Hydrogen gas sensor based on seven-core fiber interference and Pt-WO3 film

Tungsten oxide (WO3) typically owns the characteristics of electrochemical, photo-chromic, and gas-chromic. The seven-core fiber (SCF) generates a strong interference signal that comprises super-modes. The thermo-optic and thermo-expansion characteristics of SCF were utilized with an aid of Pt-WO3 film that makes the sensor highly sensitive to the H2 gas environment. The sensor with spiral micro grooves by femtosecond-laser ablation considerably enhanced the H2 sensitivity from 3.28 nm/% to 4.0 nm/%, and obtained a response and recovery time < 90 s.

1ppm-detectable hydrogen gas sensors by using highly sensitive P+/N+ single-crystalline silicon thermopiles

Hydrogen (H2) is currently of strategic importance in the pursuit of a decarbonized, environmentally benign, sustainable global energy system; however, the explosive nature of H2 requires leakage monitoring to ensure safe application in industry. Therefore, H2 gas sensors with a high sensitivity and fast response across a wide concentration range are crucial yet technically challenging. In this work, we demonstrate a new type of MEMS differential thermopile gas sensor for the highly sensitive, rapid detection of trace H2 gas in air. Facilitated by a unique MIS fabrication technique, pairs of single-crystalline silicon thermopiles (i.e., sensing and reference thermopiles) are batch fabricated with high-density single-crystalline silicon thermocouples, yielding an outstanding temperature sensitivity at the sub-mK level. Such devices ensure the detection of miniscule temperature changes due to the catalytic reaction of H2 with a detection limit as low as ~1 ppm at an operating temperature of 120 °C. The MEMS differential thermopiles also exhibit a wide linear detection range (1 ppm-2%, more than four orders of magnitude) and fast response and recovery times of 1.9 s and 1.4 s, respectively, when detecting 0.1% H2 in air. Moreover, the sensors show good selectivity against common combustible gases and volatile organics, good repeatability, and long-term stability. The proposed MEMS thermopile H2 sensors hold promise for the trace detection and early warning of H2 leakage in a wide range of applications.

Plasma-Enhanced Atomic Layer Deposition of Molybdenum Oxide Thin Films at Low Temperatures for Hydrogen Gas Sensing.

Molybdenum oxide thin films are very appealing for gas sensing applications due to their tunable material characteristics. Particularly, the growing demand for developing hydrogen sensors has triggered the exploration of functional materials such as molybdenum oxides (MoOx). Strategies to enhance the performance of MoOx-based gas sensors include nanostructured growth accompanied by precise control of composition and crystallinity. These features can be delivered by using atomic layer deposition (ALD) processing of thin films, where precursor chemistry plays an important role. Herein, we report a new plasma-enhanced ALD process for molybdenum oxide employing the molybdenum precursor [Mo(NtBu)2(tBu2DAD)] (DAD = diazadienyl) and oxygen plasma. Analysis of the film thickness reveals typical ALD characteristics such as linearity and surface saturation with a growth rate of 0.75 Å/cycle in a broad temperature window between 100 and 240 °C. While the films are amorphous at 100 °C, crystalline β-MoO3 is obtained at 240 °C. Compositional analysis reveals nearly stoichiometric and pure MoO3 films with oxygen vacancies present at the surface. Subsequently, hydrogen gas sensitivity of the molybdenum oxide thin films is demonstrated in a laboratory-scale chemiresistive hydrogen sensor setup at an operation temperature of 120 °C. Sensitivities of up to 18% are achieved for the film deposited at 240 °C, showing a strong correlation between crystallinity, oxygen vacancies at the surface, and hydrogen gas sensitivity.

Carbon nanotubes/polyaniline as hydrogen gas sensor: Optical bandgap, micro-morphology, and skin depth studies

In this study, multiwall carbon nanotubes (MWCNTs)/polyaniline nanocomposites deposited on ITO coated glass as substrate by the spin-coating technique were applied to the investigation of the effect of different contents of MWCNTs on the optical and electrical properties of polyaniline. Micrographs from an atomic force microscope were taken to analyze the 3-D microtexture parameters of surface texture factors and fractal dimension. By using optical spectroscopy of samples with different concentrations of MWNCTs in visible and ultraviolet regions, the transmission variations vs photon wavelength, optical bandgap, absorption coefficient, and skin depth were studied. The variation in the resistance of nanocomposite films exposed to 0.4 %vol of H2 gas at room temperature was monitored, and the results indicated that the sensitivity and responsibility of the composites increased with an increase in the MWCNT amount.

Application of a Charge Plasma Tunnel FET with SiGe Pocket as an Effective Hydrogen Gas Sensor

In this article, we have investigated the potential applications of a charge plasma TFET with a source pocket (SP-CPTFET) as a hydrogen gas sensor. The Si0.6Ge0.4 source pocket and HfO2 gate dielectric together greatly enhance the drain current. The presence of an intrinsic silicon body in the channel and drain controls the leakage current. Palladium (Pd) is considered the top and bottom gate catalyst for hydrogen (H2) gas sensing. The flat band voltage and CV properties of the sensor change as a result of the adsorption of H-atoms at the Pd-HfO2 and Pd surfaces. As a result, the gate work-function () modulates, affecting the drain current. The electrical analysis of the sensor is carried out in terms of transfer characteristics, band energy, current ratio, interband tunneling rate, and electric field. Additionally, the suggested sensor’s drain current sensitivity and current ratio sensitivity are estimated for various H2 pressure concentrations. The scope of the investigation has been expanded to include the effect of variation in the H2 gas pressure, germanium mole fraction, temperature, pocket length, interface trap charges (ITC), oxide thickness variation, and comparison of different catalytic metals on the drain current performance. The reported sensor exhibits a much-improved drain current sensitivity and current ratio sensitivity compared to the CPTFET gas sensor.

Colorimetric Plasmonic Hydrogen Gas Sensor Based on One-Dimensional Nano-Gratings

Plasmonic hydrogen gas sensors have become widely used in recent years due to their low cost, reliability, safety, and measurement accuracy. In this paper, we designed, optimized, and fabricated a palladium (Pd)-coated nano-grating-based plasmonic hydrogen gas sensor; and investigated using the finite-difference time-domain method and experimental spectral reflectance measurements, the calibrated effects of hydrogen gas exposure on the mechano-optical properties of the Pd sensing layer. The nanostructures were fabricated using DC sputter deposition onto a one-dimensional nano-grating optimized with a thin-film gold buffer to extend the optical response dynamic range and performance stability; the color change sensitivity of the Pd surface layer was demonstrated for hydrogen gas concentrations as low as 0.5 vol.%, up to 4 vol.%, based on the resonance wavelength shift within the visible band corresponding to the reversible phase transformation. Visual color change detection of even the smallest hydrogen concentrations indicated the high sensitivity of the gas sensor. Our technique has potential for application to high-accuracy portable plasmonic sensors compatible with biochemical sensing with smartphones.

Formation of sub-100-nm suspended nanowires with various materials using thermally adjusted electrospun nanofibers as templates

The air suspension and location specification properties of nanowires are crucial factors for optimizing nanowires in electronic devices and suppressing undesirable interactions with substrates. Although various strategies have been proposed to fabricate suspended nanowires, placing a nanowire in desired microstructures without material constraints or high-temperature processes remains a challenge. In this study, suspended nanowires were formed using a thermally aggregated electrospun polymer as a template. An elaborately designed microstructure enables an electrospun fiber template to be formed at the desired location during thermal treatment. Moreover, the desired thickness of the nanowires is easily controlled with the electrospun fiber templates, resulting in the parallel formation of suspended nanowires that are less than 100 nm thick. Furthermore, this approach facilitates the formation of suspended nanowires with various materials. This is accomplished by evaporating various materials onto the electrospun fiber template and by removing the template. Palladium, copper, tungsten oxide (WO3), and tin oxide nanowires are formed as examples to demonstrate the advantage of this approach in terms of nanowire material selection. Hydrogen (H2) and nitrogen dioxide (NO2) gas sensors comprising palladium and tungsten oxide, respectively, are demonstrated as exemplary devices of the proposed method.

Investigation of ZnO/V2O5 hybrid nanocomposite-based ultraviolet photodetector and hydrogen gas sensor

Investigation of ZnO/V2O5 hybrid nanocomposite-based ultraviolet photodetector and hydrogen gas sensor

Machine Learning-Based IOT Air Quality and Pollution Detection

In India, gas leakage from the different factories harmful to human surveying in the last fifty years is very low. However, there is a lack of prior detection of the chemical gases detection system in the situation raised. So, In this regard, there is a gap identification of chemical gases intensity detection needed. In this work, the main objective is to identify chemical gases intensity and maintain the stream data in the database from different locations. To fill this gap, that is identifying the high-intensity chemical gases from the chemical gas disaster areas. The first step needs to identify the different chemical gases and natural gas compositions. In this regard in this work for design internet-based gases in the air system. So, the sensors MQ2(Ethanol i-Butane Methane Alcohol Gas Sensor Sensor), MQ3(Sensitivity Alcohol Detector), MQ4 (Methane and Natural Gas (CNG)), MQ-5 ( LPG GAS SENSOR), MQ-7 (CO Gas Sensor Module Test Carbon Monoxide Detector), MQ-8 (hydrogen Gas Sensor), MQ-9 (carbon monoxide), MQ-135 Sensor(Air Quality Sensor Hazardous Gas Detector) and DHT11 Digital Temperature Humidity Sensors. These sensors are interfacing with the micro-control STM 32 board. It is also called one Pollution identification terminal by using it to pull the sensor stream data from location to centralized data. This stream data transportation is a service to pull the data. For this Data pulling, design an algorithm store into a cloud database. In this research work, design the electronic terminal with a wifi circuit using IoT technologies.Moreover, getting these attributes as data. Data need to apply the preprocessing techniques and extracted feature techniques also. This paper discusses mainly designing the terminal for pollution attributes , cleaning the data, and applying the Machine Learning based Feature extraction techniques.

Highly efficient reduced tungsten oxide-based hydrogen gas sensor at room temperature

Reduced tungsten oxide nanoparticles (WO2.72) was synthesized from tungsten trioxide by calcination method. The prepared samples were systematically characterized via field-emission scanning electroscope (FESEM), Raman spectroscopy, and X-ray diffraction (XRD). Then, the prepared WO2.72 was spin coated on Si/SiO2 substrate, and the sensor was developed with interdigital electrode. The gas sensing property of the developed sensor toward H2 gas was investigated. The result shows that the fabricated WO2.72 sensor possesses excellent H2 gas sensor response of 27% at room temperature. Moreover, the WO2.72 sensor exhibited outstanding long-term stability and repeatability at 500 ppm. Besides, it exhibited stable sensor response in wide range of humidity reaveviling its potential candidacy for real application of H2 gas monitoring. Therefore, this study paves way for development of effective, stable and fast responsing H2 gas sensor at room temperature that is very important in environmental remediation.

Improved Hydrogen Gas Sensing Performance of Carbon Nanotube Synthesized Using Microwave Oven

Obtaining a high-performance hydrogen (H2) gas sensor based on carbon nanotube (CNT) remains challenging. In this view, two CNT samples such as untreated (R-CNT) and nitric acid (HNO3)-treated (called functionalized or F-CNT in short) were deposited on the SiO2/Si substrate using an electrophoretic deposition technique. The structure, morphology, and electrical characteristics of these samples were evaluated. Fourier transform infrared (FTIR) spectra confirmed the presence of OH groups at the walls of nanotubes after acid treatment. Moreover, it found the current increased from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$35 \mu \text{A}$ </tex-math></inline-formula> for R-CNT to 11 mA for F-CNT. In addition, both R-CNT and F-CNT were used to fabricate H2 gas sensors. The sensing capacity of the obtained sensors was measured under the H2 gas exposure range of 20 to 300 ppm operated at room temperature (RT), 50 °C, and 75 °C. The H2 gas sensor made of F-CNT showed a much higher response (368%) and shorter response time (15 s) as well as recovery time (72 s) than the one made using R-CNT. It was asserted that the H2 gas sensing performance of the proposed sensor can significantly be improved via the acid treatment or functionalization of CNT.

Shape selective comprehensive gas sensing study of different morphological manganese-cobalt oxide based nanocomposite as potential room temperature hydrogen gas sensor

The design of morphology-based spinel structures has appeared as an effective approach for improving the performance of the sensor in hydrogen gas sensing to facilitate hydrogen economy. In this study, we report a detailed shape selective analysis of four different morphological spinel structures supported on reduced graphene oxide (rGO) as an efficient hydrogen sensor. Our study revealed that the response of manganese-cobalt oxides are strongly depended on the morphology of the system (flower, rod, flakes and sphere) which can be explained by combined effects of surface area, defects generated on the surface and crystallinity. The n-type responses of all native oxides and the composite modified with rGO indicated the formation of n-n heterojunction at their interface. The bare flower-like structure showed higher responses (S% = 6.3) with low response time (17 s) and recovery time (18 s) at higher temperature (160 °C). In comparison, the improved sensing behavior of the composite with highest response (12.77%) and lowest response-recovery time (9 s and 13 s, respectively) at room temperature can be attributed to the higher electrical conductivity of rGO with fast charge carrier mobility. Also, this novel gas sensor demonstrated superior sensitivity, higher stability, and better selectivity against various gaseous mixtures.