Performance Of Hydrogen Sensor Research Articles

Experimental study on dynamic response performance of hydrogen sensor in confined space under ceiling

With the advancement of Fuel Cell Vehicles (FCVs), detecting hydrogen leaks is critically important in facilities such as hydrogen refilling stations. Despite its significance, the dynamic response performance of hydrogen sensors in confined spaces, particularly under ceilings, has not been comprehensively assessed. This study utilizes a catalytic combustion hydrogen sensor to monitor hydrogen leaks in a confined area. It examines the effects of leak size and placement height on the distribution of hydrogen concentrations beneath the ceiling. Results indicate that hydrogen concentration rapidly decreases within a 0.5–1.0 m range below the ceiling and declines more gradually from 1.0 to 2.0 m. The study further explores the attenuation pattern of hydrogen concentration radially from the hydrogen jet under the ceiling. By normalizing the radius and concentration, it was determined that the distribution conforms to a Gaussian model, akin to that observed in open space jet flows. Utilizing this Gaussian assumption, the model is refined by incorporating an impact reflux term, thereby enhancing the accuracy of the predictive formula.

An Ultrasensitive Room-Temperature H2 Sensor Based on a TiO2 Rutile–Anatase Homojunction

Metal oxide semiconductor hetero- and homojunctions are commonly constructed to improve the performance of hydrogen sensors at room temperature. In this study, a simple two-step hydrothermal method was employed to prepare TiO2 films with homojunctions of rutile and anatase phases (denoted as TiO2-R/A). Then, the microstructure of anatase-phase TiO2 was altered by controlling the amount of hydrochloric acid to realize a more favorable porous structure for charge transport and a larger surface area for contact with H2. The sensor used a Pt interdigital electrode. At an optimal HCl dosage (25 mL), anatase-phase TiO2 uniformly covered rutile-phase TiO2 nanorods, resulting in a greater response to H2 at 2500 ppm compared with that of a rutile TiO2 nanorod sensor by a factor of 1153. The response time was 21 s, mainly because the homojunction formed by the TiO2 rutile and anatase phases increased the synergistic effect of the charge transfer and potential barrier between the two phases, resulting in the formation of more superoxide (O2−) free radicals on the surface. Furthermore, the porous structure increased the surface area for H2 adsorption. The TiO2-R/A-based sensor exhibited high selectivity, long-term stability, and a fast response. This study provides new insights into the design of commercially competitive hydrogen sensors.

Anatase TiO2 aerogel with high specific surface areas and porous network structures for ultra-fast response hydrogen sensor

To better ensure the safe preparation, storage, transportation, and use of hydrogen, it is critical to find a convenient and effective method to monitor requests. In this study, an excellent hydrogen gas sensor based on the TiO2 aerogel structure with a high specific surface area has been successfully fabricated. In addition, we have obtained TiO2 aerogel with anatase crystal form and rutile crystal form through high-temperature crystallization to further explore the influence of TiO2 nanoparticles and TiO2 aerogel crystal form on the performance of hydrogen sensors. The results show that the sensitivity of anatase TiO2 aerogel hydrogen sensor to 100 ppm H2 at 450 °C is 3.1271, higher than TiO2 nanoparticles (1.4942), amorphous TiO2 aerogel (2.1796) and rutile TiO2 aerogel hydrogen sensor (2.8464), and it exhibits ultra-rapid response recovery characteristics, with a response time of 4 s and a recovery time of 29 s, respectively. Besides, the sensitivity of anatase TiO2 aerogel hydrogen sensor to 100 ppm H2 is twice that of 100 ppm ammonia (1.5668), 2.5 times that of 100 ppm methanol (1.2731), and 1.1 times that of 100 ppm ethanol, showing that anatase TiO2 aerogel has good selectivity in a complex gas environment. The 30 days repeatability test shows that the anatase TiO2 aerogel hydrogen sensor has good stability and linearity (100–1000 ppm H2 concentration). Finally, this work proposes a hydrogen sensing model, which is used to describe the hydrogen sensing mechanism of TiO2 aerogel, indicating that the high specific surface area and high porosity of TiO2 aerogel play an important role in hydrogen detection. Hydrogen sensors based on TiO2 aerogel are rarely reported at present, and this work has an important reference and guidance role for the future in-depth industrial research of hydrogen sensors.

Improved performance of fiber-optic hydrogen sensor of porous Pt/WO3 based on ZIF-8

A novel fiber-optic hydrogen sensor including Pt/WO3 sensing material with a microporous structure is proposed and experimentally demonstrated with improved performance. The proposed Pt/WO3 sensing material is realized by introducing metal-organic frameworks (MOFs) as templates. The mesoporous structure of the ZIF-8 template improves the reactive sites of hydrogen sensitive materials with hydrogen. Hydrogen sensors were fabricated by combining the synthesized material with Fiber Bragg Gratings (FBGs) and the performance of hydrogen sensors was investigated. The experimental results show that the hydrogen sensitivity of the FBG with ZIF-8 synthesized Pt/WO3 has been increased to 0.075 pm/ppm, which is twice that without ZIF-8 synthetization. The stability and the response speed are also significantly improved. The introduction of microporous MOFs templates into Pt/WO3 sensing material will greatly accelerate the wide application of Pt/WO3-based fiber optic hydrogen sensors on hydrogen leakage detection.

Ultrasensitive and Wide‐Range Flexible Hydrogen Sensor Based on Pd Nanoparticles Decorated Ultrathin SnO2 Film

AbstractHighly sensitive and reliable hydrogen detection is prerequisite for the large‐scale implementation of green energy hydrogen. It remains a tough challenge to get a highly selective H2 sensor to low concentration H2 gas with low working temperature. In this work, high performance flexible hydrogen sensor using ultrathin SnO2 film decorated by Pd nanoparticles (NPs) on polyimide (PI) was developed based on versatile atomic layer deposition (ALD) and cluster beam deposition (CBD). The influence of Pd NPs loading amount and operating temperature on the performance of hydrogen sensors was studied. The sensors obtain an extremely high response over 20000 to 30 ppm H2 at the relatively low operating temperature of 75–125 °C. The Pd NPs@SnO2/PI sensor achieves a wide detection range of 0.1‐5000 ppm with the limit of detection (LOD) of 100 ppb at 125 °C. A low LOD of 250 ppb can still be achieved at room temperature. The sensors also exhibit outstanding sensing selectivity for hydrogen over interfering gases and excellent mechanical resistance after 2000 bending cycles. The mechanism for improved sensing performance of ALD ultrathin film with CBD‐derived noble metal NPs decoration may be a feasible strategy for the construction of highly sensitive, selective, and flexible hydrogen sensors.

Ultra-High Sensitive Fiber Optic Hydrogen Sensor in Air

A compact fiber optic hydrogen sensing system employing self-referenced configuration and controllable light heating technologies, is proposed and experimentally demonstrated with ultra-high sensitivity and wide dynamic range of hydrogen concentration detection. This sensing probe, consisting of nano WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -Pd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Pt-Pt composite films and single mode fiber inscribed with two Bragg gratings, is principally based on the gasochromic effect of sensitive films. Signal-to-noise ratio of this system can be significantly enhanced with peak intensity of high reflective fiber Bragg grating (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , FBG1 written in flat wavelength range of light source) and background intensity (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , at a spectral distance of 1nm on the red side of FBG1) as reference intensity and sensing intensity respectively. A 980 nm laser and proportion integration differentiation (PID) controller were employed to ensure the hydrogen sensitive film working at an optimized temperature of 80 °C. Hydrogen concentration detection from 0.5 to 12000 ppm in air was achieved by utilizing this sensing system. Experimental results demonstrate the resolution of this hydrogen sensing system can reach 0.2 ppm within range of 1 to 1000 ppm hydrogen exposure. Moreover, this sensor can present a quick response time of less than one second towards 4000 ppm hydrogen in air. Furthermore, the stability of this sensor can be greatly enhanced with controllable optical heating system. The approach proposed in this work can greatly improve the performance of hydrogen sensor, which is very beneficial to its potential application in hydrogen-related facilities.

Improving the Performance of Hydrogen Sensors with Novel TiO2 Nanotube Arrays Hybrid Structure

In this paper, a kind of novel TiO2 nanotube arrays (TNTs) hybrid structure was presented to improve the performance of hydrogen sensors. In this novel structure, palladium functionalized TNTs hybrid nanostructure supported on titanium wire. TNTs arrays was prepared by anodizing Ti wire using a standard electrochemical procedure. Pd nanomaterials were deposited on TNTs. Optimized experiments showed the hydrogen sensor supported on titanium wire showed a good response time of 8 s and high sensitivity of 94.8% at 1.9 vol% H2 at room temperature (25 °C). The research work revealed potential good hydrogen sensitivity of this kind of hybrid nanostructure.

Test methodologies for hydrogen sensor performance assessment: Chamber vs. flow-through test apparatus

Certification of hydrogen sensors to meet standards often prescribes using large-volume test chambers [1,2]. However, feedback from stakeholders such as sensor manufacturers and end-users indicates that chamber test methods are often viewed as too slow and expensive for routine assessment. Flow-through test methods are potentially an efficient and cost-effective alternative for sensor performance assessment. A large number of sensors can be simultaneously tested, in series or in parallel, with an appropriate flow-through test fixture. The recent development of sensors with response times of less than 1s mandates improvements in equipment and methodology to properly capture the performance of this new generation of fast sensors; flow methods are a viable approach for accurate response and recovery time determinations, but there are potential drawbacks. According to ISO 26142 [1], flow-through test methods may not properly simulate ambient applications. In chamber test methods, gas transport to the sensor is dominated by diffusion which is viewed by some users as mimicking deployment in rooms and other confined spaces. Conversely, in flow-through methods, forced flow transports the gas to the sensing element. The advective flow dynamics may induce changes in the sensor behaviour relative to the quasi-quiescent condition that may prevail in chamber test methods. The aim of the current activity in the JRC and NREL sensor laboratories [3,4] is to develop a validated flow-through apparatus and methods for hydrogen sensor performance testing. In addition to minimizing the impact on sensor behaviour induced by differences in flow dynamics, challenges associated with flow-through methods include the ability to control environmental parameters (humidity, pressure and temperature) during the test and changes in the test gas composition induced by chemical reactions with upstream sensors. Guidelines on flow-through test apparatus design and protocols for the evaluation of hydrogen sensor performance have been developed. Various commercial sensor platforms (e.g., thermal conductivity, catalytic and metal semiconductor) were used to demonstrate the advantages and issues with the flow-through methodology.

Influence of graphene growth temperature by chemical vapour deposition on the hydrogen response of palladium–graphene junction

The hydrogen sensing by palladium-graphene junction was dependent on the atmospheric pressure chemical vapour deposition growth temperature of the graphene films. The growth temperature window adopted in this study was 900–1000 °C, and the hydrogen sensor performance of the palladium–graphene junction (0.5–2.0% H2 in air) was studied in the temperature range 30–150 °C. Raman spectroscopy study with the as grown graphene films revealed the multilayer nature and the Pd–graphene planar structure showed a temperature dependent n- to p-type conductivity change in presence of hydrogen. Such a conductivity transition in presence of a reducing gas like hydrogen was experimentally studied in detail, and the hydrogen sensor results were correlated with the multilayer character of the graphene thin film, which induces hydrogen intercalation between the graphene layers.

Influence of electrical modes on performance of MISFET hydrogen sensors

The influence of the measuring circuit type and electrical modes on performance of the hydrogen sensors based on metal–insulator–semiconductor field-effect transistor (MISFET) has been studied. MISFET with structure Pd–Ta2O5–SiO2–Si was fabricated on single silicon chip together with temperature sensor and heater-resistor. The influence of the circuits’ electrical parameters on MISFET hydrogen sensors’ characteristics (conversion function, hydrogen sensitivity, errors and power consumption) has been studied by experiments and modeling. The studies have shown how the performance characteristics of MISFET-based hydrogen sensors depend on the circuits and electrical modes. The recommendations for the optimal choice of electrical modes of different circuits were formulated.

Highly sensitive hydrogen sensor based on Pd-functionalized titania nanotubes prepared in water-contained electrolyte

Highly sensitive hydrogen sensor based on palladium (Pd) nano-rings supported by titania nanotubes (TNTs) substrate has been investigated at room temperature. The TNTs substrate was prepared in various mass fraction of water contents in electrolyte from 5 to 20 %. The water content in the electrolyte increased the tube-diameter and the interstice among tubes. Pd nano-rings were deposited on TNTs substrates using DC magnetron sputtering. The sensor exhibited excellent performance at hydrogen concentrations from 0.05 to 1.6 %. We researched the detection performance of hydrogen sensors made by different TNTs substrates. When the water content was 17.5 wt%, the sensor showed a high sensitivity of 88 % at 1.6 % hydrogen concentration.

(Invited) Integration of Functional Coatings with Fiber Optics for Chemical and Medical Sensing Applications

The combination of fiber optics with nano-structure technologies and functional coatings offers great potential for the realization of novel sensor concepts. Minitured optical fiber sensors with thin films as sensitive elements could open new fields for chemical and medical sensing applications. Thin films work as sensitive elements and transducer to get response and feedback from environments, optical fiber here are employed to signal carrier. Such fiber-optic component integrated sensitive materials has intrinsic property of small size, light weight and immunity to electric-magnetic interference, and therefore would have promising perspectives in chemical and medical applications. In chemical industry, hydrogen is a clean energy and an important chemical raw material, however, hydrogen is dangerous because of its smallest molecule and flammable characteristic. Solid-state hydrogen sensors based on piezoelectric, fiber optic, semiconductor and electrochemical devices have been investigated and reported in literatures. Compared to sensing devices based on semiconductor or electrochemical principle of operation, optical fiber sensor is quite immune to an electromagnetic noise and could be safely operated in explosive environment. Novel Pt-loaded WO3 coatings has been developed as hydrogen sensing elements at the National Engineering Laboratory for Fiber Optic Sensing Technology, Wuhan University of Technology (NEL-FOST), and fiber optic hydrogen sensor based on these sensitive coatings have been investigated. Pt-loaded WO3coating with molar ratio of 1:5 has the best hydrogen sensitivity when the annealing temperature is 315°C. The corresponding hydrogen sensor has 536 pm wavelength shift towards 10000 ppm hydrogen under room temperature of 25°C. The hydrogen sensor can detect hydrogen concentration as low as 200 ppm. FBG shows nonlinear wavelength shifts for different hydrogen concentrations. Ambient humidity change has little effect on the performance of hydrogen sensor. The hydrogen sensor has good repeatability, selectivity and continuous monitoring ability during the hydrogen response. The proposed FBG hydrogen sensor may be very promising for hydrogen concentrations detection in air. In medical applications, relative-humidity (RH) is one of the main indicators for breathing and health monitoring. Fiber optics based RH measurement could be very promising due to its tiny size and low-coat of the sensing head. Minitured optical fiber sensors based on Fabry-Perot thin film structure are also proposed, the transducer deposited on fiber end-face is multilayer coating consisting of a stack of porous dielectric oxide materials. The reversible adsorption and desorption of water molecules in the porous films in dependence on water vapor shifts the reflected interference spectrum fringe, therefore humidity sensing is correlated with the shift of interference fringe. The sensing probes are porous oxide multilayer deposited on fiber tip, which forms thin film Fabry–Perot interferometer (FPI). The coatings are realized by e-beam evaporation without ion-source assistance, this will generate a porous coating stack in the FPI. Fabry–Perot interferometry sensors are extremely sensitive to perturbations that affect the optical path difference between two reflective mirrors and the sensing region can be very compact to ensure miniature size of the sensor.

ZnO:Cd nanorods hydrogen sensor with low operating temperature

In this paper, the properties of hydrogen (H2) sensor based on Cd-doped zinc oxide (ZnO:Cd) nanorods are investigated. The nanorods are synthesized using hydrothermal method and sensors are fabricated by spinning nanorods on the glass substrate. All samples show the hexagonal phase of wurtzite, and their XRD diffraction peaks shift slightly to lower 2θ angle when the concentration of Cd increase. The cadmium dopant plays a vital role in fine tuning the structure of crystal and the size of rods, and it also enhances the stability of ZnO. Via Cd-doping, the performance of hydrogen sensors based on ZnO nanorods improves significantly. Among all sensors doped with various Cd concentration, the 2 at% Cd-doped sensor performs best, since it is able to detect 500 ppm hydrogen at relatively lower operating temperatures ranging from 50 °C to 100 °C with faster response and shorter recovery time.

Effect of Irradiation on Hydrogen Sensors Based on MISFET

The electron irradiation effect on hydrogen sensitivity of the sensors based on metal-insulator-semiconductor transistor (MISFET) element with structure Pd-Ta2O5-SiO2-Si have been investigated. The MISFET threshold voltage as a function of hydrogen concentration was determined before and after each irradiation. It is found that under irradiation this function was monotonically drifting. In addition after irradiations by doses more than ∼ 700Gy the hydrogen sensitivity are steadily decreasing. The models of hydrogen and radiation sensitivity were developed. According to represented models the estimations of critical doses and the forecast of hydrogen sensor performance under irradiation have been done.

High Sensitivity of Hydrogen Sensing Through N-polar GaN Schottky Diodes

AbstractN-polar and Ga-polar GaN grown on c-plane sapphire by a metal-organic chemical vapor deposition (MOCVD) system were used to fabricate platinum deposited Schottky contacts for hydrogen sensing at room temperature. Wurtzite GaN is a polar material. Along the c-axis, there are N-face (N-polar) or Ga-face (Ga-polar) orientations on the GaN surface. The Ohmic contacts were formed by lift-off of e-beam deposited Ti (200 Å)/Al (1000 Å)/Ni (400 Å)/Au (1200 Å). The contacts were annealed at 850°C for 45 s under a flowing N2 ambient. Isolation was achieved with 2000 Å plasma enhanced chemical vapor deposited SiNx formed at 300°C. A 100 Å of Pt was deposited by e-beam evaporation to form Schottky contacts. After exposure to hydrogen, Ga-polar GaN Schottky showed 10% of current change, while the N-polar GaN Schottky contacts became fully Ohmic. The N-polar GaN Schottky diodes showed stronger and faster response to 4% hydrogen than that of Ga-polar GaN Schottky diodes. The abrupt current increase from N-polar GaN Schottky exposure to hydrogen was attributed to the high reactivity of the N-face surface termination. The surface termination dominates the sensitivity and response time of the hydrogen sensors made of GaN Schottky diodes. Current-voltage characteristics and the real-time detection of the sensor for hydrogen were investigated. These results demonstrate that the surface termination is crucial in the performance of hydrogen sensors made of GaN Schottky diodes.

AlGaN/GaN Schottky diode hydrogen sensor performance at high temperatures with different catalytic metals

Schottky diodes on AlGaN/GaN heterostructures with Pt, IrPt, and PdAg catalytic metals are fabricated and characterized from 200 °C to 800 °C for H 2 sensing. Over this large range of temperature, the forward current of all the diodes increases with exposure to H 2 gas, which is attributed to Schottky barrier height reduction caused by the atomic hydrogen absorption on the metal–oxide interface. The results indicate that AlGaN/GaN heterostructure Schottky diodes are capable of high-temperature H 2 sensor operation up to 800 °C. As temperature increases, the hydrogen detection sensitivity of Pt and IrPt diodes improves due to the more effective H 2 dissociation. However, the sensitivity of PdAg diodes degrades with the increase of temperature due to thermal instability of PdAg. At a range of temperature from 200 °C to 300 °C, PdAg diodes exhibit significant higher sensitivity compared with Pt and IrPt diodes. IrPt and Pt diodes show higher sensitivity at temperatures above 400 °C.