Hydrogen Gas In Air Research Articles

Hydrogen sensing characteristics of an Al-doped SnO2 thin film incorporated with palladium nanoparticles

An interesting hydrogen sensor prepared by an Al (3 at %)-doped SnO2 (ATO) thin layer decorated with palladium nanoparticles (Pd NPs) is demonstrated herein. The related hydrogen detecting characteristics are systematically investigated. The elemental and intrinsic properties are characterized by high-resolution scanning electron microscopy (HRSEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The specific surface area and catalytic ability are remarkably enhanced due to the presence of Pd NPs on the ATO thin layer. This causes the considerable improvement of hydrogen sensing behaviors. Under introduced 1000 ppm hydrogen gas in air, a higher sensing response of 3152 with a corresponding response and a recovery times of 17 s and 4 s and a lower detectable concentration of 50 ppb H2/air are obtained at 225 °C for the studied Pd NP/ATO sensor. In addition, the studied sensor shows good repeatability and long-term stability. From a kinetic adsorption analysis, an activation energy about 43.6 kJ mol−1 is observed for this hydrogen detecting action. The studied Pd NP/ATO sensor also shows favours, e.g., simple device structure, easy production, lower consumed power, and a widespread sensing region of hydrogen gas content.

Abstract 10368: The Safety and Tolerability of Prolonged Inhalation of Hydrogen Gas in Air: A Phase I Clinical Trial

Introduction: Ischemia reperfusion injury (IRI) is central to many critical illnesses, including cardiac arrest, myocardial infarction, and stroke. Inhaled hydrogen gas (H2) has been shown to diminish IRI in a number of preclinical models, in part by the selective reduction of oxyradical species. Methods: Following FDA and IRB approval of this Investigator-Initiated Phase I IND study (NCT04046211), 8 healthy participants underwent hospitalized exposure to 2.4% H2 in medical air via high flow nasal cannula (15 LPM) for either 24 hours (n=2), 48 hours (n=2), or 72 hours (n=4). Screening for adverse effects included periodic nurse-adjudicated assessments using Common Terminology Criteria for Adverse Events (CTCAE, v5.0); regularly-spaced vital signs, pulmonary function testing, and mini-mental state exam (MMSE); EKG and serologic testing prior to versus following exposure. Data were compared over time using Wilcoxon matched-pairs signed rank test. All AE assignments were verified by two clinicians external to the study team and an external DSMB. Results: Eight adult participants (18-30 years; 50% female; 62% non-Caucasian) completed the study without early termination. No symptoms or clinically significant adverse events occurred in any patient. Compared with baseline measures, there were no significant changes over time in blood pressure, heart rate, oxygen saturation, or respiratory rate (A). There were no significant changes in PFTs (B), MMSE scores (C), EKG measurements (D) or serologic tests for hematologic (except for clinically-insignificant increases in hematocrit and platelet counts), renal, hepatic, pancreatic, or cardiac injury (E) associated with H2 inhalation. Conclusion: Inhalation of 2.4% H2 gas does not appear to cause clinically significant adverse effects in healthy adults. These data will be foundational to future interventional studies of inhaled H2 in injury states, including following cardiac arrest.

Safety of Prolonged Inhalation of Hydrogen Gas in Air in Healthy Adults.

Prospective, single-arm study. Tertiary care hospital. Eight healthy adult participants. Subjects underwent hospitalized exposure to 2.4% hydrogen gas in medical air via high-flow nasal cannula (15 L/min) for 24 (n = 2), 48 (n = 2), or 72 (n = 4) hours. Endpoints included vital signs, patient- and nurse-reported signs and symptoms (stratified according to clinical significance), pulmonary function testing, 12-lead electrocardiogram, mini-mental state examinations, neurologic examination, and serologic testing prior to and following exposure. All adverse events were verified by two clinicians external to the study team and an external Data and Safety Monitoring Board. All eight participants (18-30 yr; 50% female; 62% non-Caucasian) completed the study without early termination. No clinically significant adverse events occurred in any patient. Compared with baseline measures, there were no clinically significant changes over time in vital signs, pulmonary function testing results, Mini-Mental State Examination scores, neurologic examination findings, electrocardiogram measurements, or serologic tests for hematologic (except for clinically insignificant increases in hematocrit and platelet counts), renal, hepatic, pancreatic, or cardiac injury associated with hydrogen gas inhalation. Inhalation of 2.4% hydrogen gas does not appear to cause clinically significant adverse effects in healthy adults. Although these data suggest that inhaled hydrogen gas may be well tolerated, future studies need to be powered to further evaluate safety. These data will be foundational to future interventional studies of inhaled hydrogen gas in injury states, including following cardiac arrest.

Microstructured FBG hydrogen sensor based on Pt-loaded WO3.

Hydrogen gas sensing properties of Pt-WO3 films on spiral microstructured fiber Bragg grating (FBG) has been demonstrated. Pt-WO3 film was prepared by hydrothermal method. The spiral microsturctured FBG was fabricated using femtosecond laser. Spiral microstructure FBG hydrogen sensor can detect hydrogen concentration from 0.02% H2 to 4% H2 at room temperature, and the response time is shortened from a few minutes to 10~30 s. Double spiral microstructure at pitch 60 μm and sputtered with 2 μm Pt-WO3 film recorded hydrogen sensitivity of 522 pm/%(v/v) H2 responding to hydrogen gas in air. This translated to approximately 2~4 times higher than the unprocessed standard FBG. The humidity has little effect on the sensing property. The sensor has fast response time, good stability, large detection range and has the good prospect of practical application for hydrogen leak detection.

FBG hydrogen sensor based on spiral microstructure ablated by femtosecond laser

This paper proposed and demonstrated fiber Bragg grating (FBG) hydrogen sensor by integrating optical fiber laser micro-machining and thin film technology. The spiral microstructure ablated sensor probe was sputtered with hydrogen sensitive material, palladium-silver (Pd-Ag) composite film, in which the atomic ratio of the two metals is controlled at Pd:Ag=4:1. Experimental work was conducted at ambient temperature and relative humidity of 25°C and 32% respectively. Double spiral microstructure at pitch 90μm and sputtered with 520nm Pd/Ag film recorded hydrogen sensitivity of 51.5 pm/%H responding to hydrogen gas in air. This translated to approximately 7.5 times higher than the unprocessed standard FBG. The sensor’s hydrogen response is reversible, has improved response time and could have potential for hydrogen gas monitoring.

Enhanced H2gas sensing properties of Au@In2O3core–shell hybrid metal–semiconductor heteronanostructures

The interest in hybrid nanoparticles (NPs) arises from their combined and often synergetic properties exceeding the functionality of the individual components. Herein, a general, environmentally friendly, and facile hydrothermal approach to synthesizing the metal–semiconductor, Au@In2O3 core–shell heteronanostructures, is described. These Au@In2O3 core–shell NPs are used as chemiresistive gas sensors for the detection of hydrogen gas in air. The sensor device based on Au@In2O3 core–shell NPs showed ∼4 times greater response and is also more selective to H2 gas compared to the In2O3 NPs sensor device. The enhanced activity can be attributed to the catalytic effect of Au, and synergistic interactions between the Au and In2O3 NPs formed in the core–shell heteronanostructures in such a way that favors the efficient electron transfer at the interface. The hydrogen sensing behavior is dependent on the redox reaction between the H2 and chemisorbed oxygen species.

Surface chemistry of neat tin oxide sensor for response to hydrogen gas in air

The response of a neat tin oxide device to hydrogen gas in air was analyzed in detail, shedding light on the surface chemistry involved. The response was clearly divided into two categories depending on the partial pressure of hydrogen (PH2), one in which the response was controlled by the reaction of O2− ions (at small PH2) and another in which the response was by that of O− ions (at higher PH2). Typical of the former category, a threshold PH2 appeared, indicating that the O− ions had been produced transiently through the reaction of O2− ions. Interestingly, a considerable amount of O2− ions was shown to persist even in the stage of the latter category, leading to an increase in resistance. Mechanism of switching between the two categories, the persistent amount of O2− ions and the meaning of the threshold PH2 could be accounted for satisfactorily based on the diagram of partition of the transferred electrons between O− and O2−. The characteristic quantities of the response in the two categories were evaluated.

(Invted) Catalytically Accelerated Hydrogen Gas Detection at Electrodeposited Pd@Pt Nanowires

Platinum (Pt)-modified palladium (Pd) nanowires (or Pd@Pt nanowires) are prepared with control of the Pt coverage. These Pd@Pt nanowires are used as resistive gas sensors for the detection of hydrogen gas in air, and the influence of the Pt surface layer is assessed. Pd nanowires with dimensions of 60 nm(h) × 200 nm(w) × 20 μm(l) are first prepared using lithographically-patterned nanowire electrodeposition (LPNE). A thin Pt surface layer is elec- trodeposited conformally onto a Pd nanowire at coverages, θPt , of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy coupled with scanning electron microscopy and electrochemical measurements are consistent with a layer-by-layer deposition mode for Pt on the Pd nanowire surface. The resistance of a single Pd@Pt nanowire is measured during the exposure of these nanowires to pulses of hydrogen gas in air at concentrations ranging from 0.04 to 5.0 vol%. Both Pd nanowires and Pd@Pt nanowires show a prompt increase in resistance upon exposure to H2 in air, caused by the conversion of Pd to more resistive PdHx. The Pt surface layer present at Pd@Pt nanowires modifies the response to H2 in two ways: First, the amplitude of the resistance change is reduced as θPt is increased, and second, the rate at which the nanowire resistance attains a new steady-state value upon a change in the H2 concentration - characterized by the response time and the recovery time - is accelerated. An optimum Pt coverage of θPt = 1.0 ML is seen for which nanowire response is accelerated by a factor of 2-3 while the recovery from H2 exposure is faster by an order of magnitude as compared to a pure Pd nanowire operating at the same elevated temperature.

Catalytically activated palladium@platinum nanowires for accelerated hydrogen gas detection.

Platinum (Pt)-modified palladium (Pd) nanowires (or Pd@Pt nanowires) are prepared with controlled Pt coverage. These Pd@Pt nanowires are used as resistive gas sensors for the detection of hydrogen gas in air, and the influence of the Pt surface layer is assessed. Pd nanowires with dimensions of 40 nm (h) × 100 nm (w) × 50 μm (l) are first prepared using lithographically patterned nanowire electrodeposition. A thin Pt surface layer is electrodeposited conformally onto a Pd nanowire at coverages, θPt, of 0.10 monolayer (ML), 1.0 ML, and 10 ML. X-ray photoelectron spectroscopy coupled with scanning electron microscopy and electrochemical measurements is consistent with a layer-by-layer deposition mode for Pt on the Pd nanowire surface. The resistance of a single Pd@Pt nanowire is measured during the exposure of these nanowires to pulses of hydrogen gas in air at concentrations ranging from 0.05 to 5.0 vol %. Both Pd nanowires and Pd@Pt nanowires show a prompt and reversible increase in resistance upon exposure to H2 in air, caused by the conversion of Pd to more resistive PdHx. Relative to a pure Pd nanowire, the addition of 1.0 ML of Pt to the Pd surface alters the H2 detection properties of Pd@Pt nanowires in two ways. First, the amplitude of the relative resistance change, ΔR/R0, measured at each H2 concentration is reduced at low temperatures (T = 294 and 303 K) and is unaffected at higher temperatures (T = 316, 344, and 376 K). Second, response and recovery rates are both faster at all temperatures in this range and for all H2 concentrations. For higher θPt = 10 ML, sensitivity to H2 is dramatically reduced. For lower θPt = 0.1 ML, no significant influence on sensitivity or the speed of response/recovery is observed.

Boron-Doped Si0.8Ge0.2 Thin Film Deposited by Helicon Sputtering for Microthermoelectric Hydrogen Sensor

A boron-doped thin film of thickness was deposited by helicon sputtering. Thermal annealing was carried out to crystallize as-deposited amorphous-like thin films. The thermoelectric properties of the films, such as an electrical conductivity, a carrier concentration, a mobility, and a Seebeck coefficient, were investigated. As a result, the films by helicon sputtering exhibited finer grains and smoother surface than those of the film deposited by conventional radio frequency (rf) sputtering. The film deposited by helicon sputtering with an rf induction coil power of and annealed at for showed a resistivity of , a Seebeck coefficient of , a Hall mobility of , and a carrier concentration of at . A microthermoelectric hydrogen sensor (micro-THS) with the boron-doped thin film and annealed at for showed high sensitivity for hydrogen gas in air. This sensor could have wide detection range of hydrogen concentration from to 3%. At an operating temperature of , for the low hydrogen concentration of , clear response was shown by the micro-THS with the film deposited by helicon sputtering and annealed at for .

Characterization of reflectivity inversion, α- and β-phase transitions and nanostructure formation in hydrogen activated thin Pd films on silicon based substrates

Optically thin palladium metal films evaporated on different silicon based substrates are investigated following exposure to different concentrations of hydrogen gas in air. Laser modulated reflectance off the palladium surface of silicon oxide and silicon nitride substrates is used to recover information regarding the reflectivity inversion and α/β-phases of the palladium complex after both first and multiple gas cycling. Atomic force microscopy confirms the formation of metal nanostructures following exposure to hydrogen of the optically thin palladium films.

Optically thin palladium films on silicon-based substrates and nanostructure formation: effects of hydrogen

Optically thin palladium films evaporated on different silicon-based substrates are investigated following exposure to different concentrations of hydrogen gas in air. Laser modulated reflectance off the palladium surface of silicon oxide, silicon nitrite and polycrystalline silicon substrates is used to recover information regarding changes in optical properties of the samples due to the absorption of hydrogen. Simple index of refraction arguments are sufficient to explain the results. Structural changes of the palladium films have been investigated using atomic force microscopy before and after hydrogen exposure. An interesting nanostructure formation is evident in some of the samples, leading to a possible means of fabricating nanodevices.

Microstructure and hydrogen gas sensitivity of amorphous (Ba,Sr)TiO 3 thin film sensors

Ferroelectric (Ba 0.67Sr 0.33)Ti 1.02O 3 thin films have been prepared by the sol–gel technology and characterized using TGA, DTA, XRD, TEM, dielectric characterizations, and gas sensing properties. The (Ba 0.67Sr 0.33)Ti 1.02O 3 thin film devices are made on Pt-coated Si substrate to detect hydrogen gas and to study gas sensing mechanism. Experimental results show that the diode I– V behavior appears in these Pd/amorphous (Ba,Sr)TiO 3 (BST) thin film/metal capacitive devices, and that the enhanced voltage shift as large as 4.5 V at 1042 ppm hydrogen gas in air has been observed. Compared with the available data in the literature, this obtained value of voltage shift in our experiment is about seven times larger than the best one reported under similar testing conditions. It has been clearly shown that the hydrogen-induced voltage shift is closely correlated with the microstructure of ferroelectric thin films and the enhancement of this polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. In this paper, we report our experimental results of this new hydrogen gas sensor and discuss the relationship between microstructure and hydrogen gas sensitivity in these ferroelectric thin film sensors.

Preparation, Property, and Mechanism Studies of Amorphous Ferroelectric (Ba, Sr)TiO3 Thin Films for Novel Metal–ferroelectric–metal Type Hydrogen Gas Sensors

Ferroelectric(Ba0.67Sr0.33)TixO3 (BST) thin films with x = 0.98, 1.00, 1.02, and 1.04 were prepared by the sol-gel technology, and their thermal, structural, dielectric, and gas sensing properties were systematically characterized. The amorphous (Ba0.67Sr0.33)TixO3 thin film capacitive devices were made on Si substrate to detect hydrogen gas and to study hydrogen-induced interfacial polarization potential.Experimental results showed that the Schottky I–V behavior appears in these Pd/amorphous BST thin film/metal capacitive devices and that enhanced interfacial dipole potentials as large as 4.5 V at 1000 ppm hydrogen gas in air were newly observed, which is about 7 times larger than the best value reported under similar testing conditions. It was clearly shown that the hydrogen-induced interfacial polarization potential is closely correlated with the microstructure of ferroelectric thin films and the enhancement of this interfacial polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. A simple hydrogen interface-blocking model is also presented to explain this interesting phenomenon.

Hydrogen-sensitive I– V characteristics of metal–ferroelectric gas sensor device fabricated by sol–gel technique

A new type of metal–ferroelectric gas sensor device was fabricated on platinum-coated n-type silicon with an amorphous ferroelectric (Ba 0.67Sr 0.33)Ti 1.02O 3 (BST) layer of thickness 125 nm prepared by the sol–gel technique and annealed at temperatures ranging from 400 to 650°C. A layer of palladium 50 nm thick was deposited through an evaporation mask, and a layer of gold 400 nm thick was then deposited to provide the electrical contact. Measurements were made for the current–voltage characteristics and their time dependence before and after the introduction of hydrogen gas. The devices showed good hydrogen sensitivity of greater than 30 nA at the operating temperature range of 230–270°C. The I– V curve shift of 750 mV to 4.6 V was detected under the influence of 5–1042 ppm of hydrogen gas in air. The effects of bias voltage and operating temperature on the response and recovery times were studied. A model is also proposed in this paper to explain the key role played by the hydrogen ions at the metal–ferroelectric heterostructure interface and the related large Schottky barrier height-lowering phenomenon.

Amorphous ferroelectric (Ba0.67Sr0.33)Ti1.02O3 thin films with enhanced H2 induced interfacial polarization potential

Ferroelectric (Ba0.67Sr0.33)Ti1.02O3 thin films have been prepared by the sol-gel technology and characterized using thermogravimetric analysis, differential thermal analysis, x-ray diffraction, dielectric characterizations, and gas sensing measurements. The (Ba0.67Sr0.33)Ti1.02O3 thin film capacitive devices are made on Si substrate to detect hydrogen gas and to study hydrogen induced interfacial polarization potential. Experimental results show that the Schottky I–V behavior appears in these Pd/amorphous (Ba,Sr)TiO3 thin film/metal capacitive devices, both in air and in diluted hydrogen gas environment, and that the enhanced interfacial dipole potential as large as 4.5 V at 1042 ppm hydrogen gas in air has been observed. Compared with the available data in the literature, the obtained value of hydrogen induced interfacial polarization potential in our experiment is about seven times larger than the best one reported under similar testing conditions. It has been clearly shown that the hydrogen induced interfacial polarization potential is closely correlated with the microstructure of ferroelectric thin films and the enhancement of this interfacial polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. A model is also proposed to explain this interesting phenomenon. In this model, hydrogen H2 molecules are dissociated at the top surface of the catalytic Pd layer and ionized under the positive bias. The H+ ions then diffuse through this Pd layer, accumulate at the interface between the Pd layer and the amorphous ferroelectric passivation film. Dipoles are thus formed so that the polarization potential is built up at the interface. Moreover, the high dielectric constant of ferroelectric films enhances dipole polarization, thus greatly improves the H2 gas induced polarization potential. Though in a preliminary stage, our experimental results offer great promise in fabricating large-scale, Si based ferroelectric thin film gas sensors and related electronic devices.

Some considerations of the lean flammability limits of mixtures involving hydrogen

Consistent data regarding the flammability limits of homogeneous mixtures of hydrogen gas in air at atmospheric pressure are presented for various temperatures extending down to −130 °C. The retardation of the combustion of lean homogeneous mixtures of hydrogen and air due to the homogeneous mixing of inerts such as CO 2, N 2 and He is also considered. Moreover, the enhancement of the flammability limits of fuel mixtures involving CO, CH 4, C 3H 8 and C 2H 4 in air due to the presence of some hydrogen is also presented. Guidelines are then suggested for predicting the role of the presence of hydrogen in the fuel-air mixtures over a wide range of concentrations and temperatures.

A hydrogen−sensitive MOS field−effect transistor

An MOS transistor in silicon with 10−nm silicon dioxide as gate insulator and 10−nm palladium as gate electrode was fabricated. The threshold voltage of this transistor was found to be a function of the partial pressure of hydrogen in the ambient atmosphere. At a device temperature of 150 °C it was possible to detect 40 ppm hydrogen gas in air with response times less than 2 min.