Hydrogen Gas Concentration Research Articles

Action mechanism of hydrogen gas on deposition of HfC coating using HfCl4-CH4-H2-Ar system

Hafnium carbide coatings were deposited on carbon/carbon composites by low pressure chemical vapor deposition using HfCl4-CH4-H2-Ar system. The microstructure, mechanical and ablation resistance performance of HfC coatings deposited with various H2 concentrations were investigated. The effect of hydrogen gas on the deposition of HfC coating was also discussed. Results show that all of the deposited coatings are composed of single cubic HfC phase, the hydrogen gas acted as a crucial role in determining the preferred orientation, microstructure and growth behavior of HfC coatings. During the deposition process, the gas phase supersaturation of the reaction species can be controlled by adjusting the hydrogen gas concentration. When deposited with low hydrogen gas concentration, the coating growth was dominated by the nucleation of HfC, which results in the particle-stacked structure of HfC coating. Otherwise, the coating growth was dominated by the crystal growth at high hydrogen gas concentration, which leads to the column-arranged structure of HfC coating. Under the ablation environment, the coating C2 exhibits better configurational stability and ablation resistance. The coating structure has a significant influence on the mechanical and ablation resistance properties of HfC coating.

Substrate Integrated Waveguide Phase Shifter for Hydrogen Sensing

This letter presents a novel environmental sensor for hydrogen detection. The new sensor is based on a passive microwave substrate integrated phase shifter in which the phase shift of the output signal varies in function of the hydrogen gas concentration. The proposed structure uses tin oxide (SnO2) micro powder as a hydrogen-sensing material and exhibits a phase variation of 19.5° in the hydrogen range of 0 to 1.6%. The substrate integrated sensor presents a new solution for environmental sensing which has the advantage of being passive and having a simple and low-cost manufacturing process.

Hydrogen Optical Metamaterial Sensor Based on Pd Dendritic Nanostructures

AbstractIn this manuscript we present a new type of hydrogen optical metamaterial sensor based on the fabrication of Pd dendritic nanostructures. The fabrication of the sensor relies on a cheap self‐assembly process based on the pulsed electrodeposition method in nanoporous alumina templates. By performing optical transmission measurements, we demonstrate how this sensor can monitor hydrogen gas concentrations at room temperature either by evaluating the rate of signal decay during the Pd hydrogen absorption (transient regime) or by measuring the total variation in signal once the system achieves the equilibrium state (stationary regime). We take into account the effects of the Pd‐hydrogen phase transition and its size dependency to explain the kinetics of the hydrogen absorption and desorption in the studied samples. By using the transient detection method, the sensor is able to detect in approximately 50 s the explosive H2(g) concentration threshold of 4 % v/v at atmospheric pressure and room temperature.

Characterization and hydrogen gas sensing performance of Al-doped ZnO thin films synthesized by low energy plasma focus device

Nanocrystalline Al-doped ZnO (AZO) thin films were deposited on glass substrates at room temperature by Mather-type plasma focus device using a ZnO target with an Al content of 3 wt%. The effect of number of focus shots on the microstructure, elemental composition, surface morphology and H2 gas sensor performance of AZO deposited thin films were investigated. X-ray diffraction (XRD) analysis confirmed the polycrystalline nature of the all deposited AZO thin films. XRD results also indicated strong dependence of crystallinity and crystallite size of deposited thin films on number of focus shots. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses led to the conclusion that the size of grains/clusters on the surface of thin films and the surface roughness of deposited samples enhance with increasing of focus shots. The experiments and measurements involving the AZO deposited thin films towards hydrogen were carried out at different operating temperatures within 150–400 °C for various concentrations of hydrogen in air. The H2 sensing response enhanced with concentration and operating temperature, and reached its maximum at 300 °C–1000 ppm concentration of hydrogen gas. The results also indicated shorter response times for samples deposited with less focus shots.

High-value resource recovery products from waste tyres

A novel process has been developed which enables the production of high-value carbon nanotubes (CNTs) and hydrogen-rich syngas from the two-stage pyrolysis–catalysis of waste tyres. The waste tyre samples originated from truck tyres and from car tyres. In addition, three of the main rubber elastomers used in tyre manufacture, polybutadiene rubber, styrene–butadiene rubber and natural rubber, were also investigated. The waste car tyres produced a syngas yield of 30·2 wt%, which was composed largely of hydrogen (53·8 vol%) with a calorific value of 18·8 MJ/m3. Increasing the tyre:catalyst ratio increased the yield of hydrogen. The component rubber elastomers produced much higher yields of syngas and hydrogen gas concentration. The carbon deposited on the catalyst during reaction was found to be mostly composed of graphitic CNTs. Changing the process conditions in terms of tyre:catalyst ratio could increase the yield of the carbon deposited on the catalyst to up to 14 wt%.

Sensitivity Enhancement of a Pd/Co Bilayer Film for Hydrogen Gas Sensing Using a Perpendicular-to-Plane Ferromagnetic Resonance Configuration

Previously, it has been shown that the strength of the perpendicular magnetic anisotropy (PMA) of thin palladium (Pd)–cobalt (Co) bilayer films can be modified when hydrogen gas is absorbed by the Pd layer. In our recent work, we showed that the ferromagnetic resonance (FMR) response of this material is sensitive to the changes in PMA upon exposure of Pd to hydrogen gas. As such, a simple, compact, and contactless hydrogen gas sensor could exploit the FMR-based detection of the reversible hydrogen-gas-induced changes in PMA. The magnitude of the FMR peak shift is critical to determining detection sensitivity: the higher the FMR peak shift at a given hydrogen gas concentration, the higher the sensitivity. Here, we demonstrate that the detection sensitivity is enhanced when the static magnetic field is applied perpendicular to the film plane. This is due to the frequency large shift, which is eight times larger than in the in-plane FMR configuration studied previously. An analysis based on the Kittel equation for FMR frequencies of an FM film is carried out in order to understand the mechanism of sensitivity enhancement. The result is important for optimizing Pd/Co bilayered thin films for use in novel platforms for hydrogen gas sensing.

Nanopatterning‐Enhanced Sensitivity and Response Time of Dynamic Palladium/Cobalt/Palladium Hydrogen Gas Sensors

Clear advantages of nanopatterned Pd/Co films over continuous Pd/Co films are demonstrated as candidates for future hydrogen gas sensing devices based upon hydrogen‐absorption‐modified ferromagnetic resonance. Nanopatterning results in a higher sensitivity to hydrogen gas and a much faster hydrogen desorption rate. It also avoids the need for an external biasing magnetic field which may be important for practical sensor implementation. A wide range of hydrogen gas concentrations has been detected with the nanopatterned material: from 0.1% to 50%, across the threshold of hydrogen flammability in air (4%).

Growth, characterization, and investigation of H2 gas sensing performance of Al-doped ZnO thin films synthesized by plasma focus device

This paper reports characterization of Al-doped ZnO (AZO) thin films deposited on glass substrates at room temperature by a low energy (1.3 kJ) plasma focus device using a ZnO target with an Al content of 3wt%. A particular focus of investigation is on properties relevant to the usage of thin films as hydrogen gas sensors. Indeed, the dependence of angular position of substrate on structural, morphological and gas sensing properties of AZO thin films is investigated. The results obtained from X-ray diffraction (XRD) reveal that all the films are of polycrystalline zinc oxide in nature, possessing hexagonal wurtzite structure. Also XRD results indicate strong dependence of crystallinity of deposited thin films on angular position of samples. Scanning electron microscopy and atomic force microscopy results reveal the structure growth and enhancement of surface roughness with decreasing the angle with respect to anode axis. The experiments and measurements involving the AZO deposited thin films towards hydrogen were carried out at different operating temperatures within 150–400 °C for various concentrations of hydrogen in air. The H2 sensing response enhanced with concentration and operating temperature, and reached its maximum at 300 °C to 1000 ppm concentration of hydrogen gas. The results also indicated shorter response times for samples deposited at larger angular positions.

Fiber Bragg Gratings Hydrogen Sensor for Monitoring the Degradation of Transformer Oil

In this paper, two fiber Bragg gratings (FBGs) sensors, which are based on different palladium (Pd) coatings ratios, was proposed to detect the dissolved hydrogen gas content in transformer oil. The FBG samples were prepared using a physical vapor deposition technique. Two samples were prepared with different Pd coating compositions. The first sample was coated with 100% Pd (Pd100), and the second sample was coated with mixture of Pd chromium (Pd58Cr42) that has a ratio of 58:42. Pd100 sensor showed faster response to dissolved hydrogen than the Pd58Cr42 sensor. In addition, the Pd100 sensor exerted higher strain at lower dissolved hydrogen content to the FBG compared with the Pd58Cr42 sensor. The Pd100 sensor has higher sensitivity, and the response range is limited to lower hydrogen content. This paper has showed the potential of using alloy like chromium to the Pd metal to enhance the dissolved hydrogen detection range.

(Invited) Photoelectrochemical Systems for Sunlight Driven Fuel Production

Photoelectrochemistry and photocatalysis have been attracted huge attentions as a promising mean to convert solar energy to storable and conveyable energy carriers such as hydrogen, formic acid, and methylcyclohexane (MCH). Hydrogen is the most promising candidate among the energy carriers because of its simple production through decomposition of abundant water and usability in combustion engines and fuel cells with no emissions except for water. In the present study, we investigated hydrogen evolution through overall water splitting, and MCH evolution through reduction of toluen in existence of water as a reductant without external bias voltage. Photoelectrochemical (PEC) water splitting using the combination of photocathode and photoanode is one of the promising means to produce hydrogen via water splitting under sunlight. The configuration can relax the criteria for the photoelectrode used in the PEC cell and allows us to use photocatalytic materials with narrower bandgap resulting in utilization of larger wavelength region in sunlight spectrum. Considering the PEC cell composed of combined photocathode and photoanode, both photocathode and photoanode should show enough large photocurrent at around 0.6 V vs. reversible hydrogen electrode (RHE) under sunlight. We found that the solid solution of ZnSe and Cu(In, Ga)Se2 (ZnSe:CIGS) with optimal composition shows relatively large cathodic photocurrent with high onset potential under simulated sunlight of AM1.5G. As shown in figure 1, ZnSe poses proper band edge potentials. However, its bandgap is not enough narrow to capture sunlight efficiently. On the other hand, CIGS have enough narrow bandgap of 1.1 eV while its potential of valence band maximum is too shallow resulting in not enough high onset potential of cathodic photocurrent to construct PEC cell with photoanode as discussed above. To achieve photocathode material with preferable band edge potentials for water splitting and sunlight absorption, ZnSe:CIGS was investigated. The solid solution with optimal composition of ZnSe0.15:CIGS0.85 act as photocathode and its cathodic photocurrent is largely enhanced by surface modifications with CdS and Pt as the case of other chalcogenide photocathodes. The PEC cell composed of ZnSe:CIGS based photocathode and BiVO4 based photoanode in side-by-side configuration showed stoichiometric water splitting under simulated sunlight with solar-to-hydrogen conversion efficiency of ~1% without external bias voltage.As discussed above, hydrogen is the promising energy carrier while the energy concentration of hydrogen gas is very thin in atmospheric pressure. Thus, pressure rising and/or liquefaction are indispensable to convey and to store. MCH is the one of the promising hydrogen carrier because of its outstanding high hydrogen concentration comparable to liquefied hydrogen. We investigated MCH production through an addition reaction of toluene with existence of reductant, water, using two-chamber PEC cell combined with membrane-electrode assembly. The PEC cell with SrTiO3 photoanode prepared by particle transfer method and MEA composed of Pt loaded carbon and anion exchange membrane showed MCH production spontaneously. We will discuss about PEC MCH production in detail in the presentation. Figure 1

Co-gasification of coal/sewage sludge blends to hydrogen-rich gas with the application of simulated high temperature reactor excess heat

The experimental study on oxygen and steam gasification and co-gasification of hard coal and sewage sludge to hydrogen-rich gas was performed in the laboratory scale fixed bed gasifier equipped with an auxiliary gasification agents pre-heating system, simulating the utilization of an excess High Temperature Reactor (HTR) heat. The allothermal gasification and co-gasification tests were performed on fuel blends of coal and sewage sludge of the total mass of 10 g and biowaste content of 20% and 40%w/w in three system configurations. In the first one the reactor was heated up with a resistance furnace to the temperature of 700 °C in the inert gas (nitrogen) atmosphere. When the temperature inside the reactor was stable, oxygen and steam of the temperature of approximately 100 °C were introduced into the reactor. In the second system, after the reactor was heated up to 700 °C, the heating of the reactor was switched off and oxygen and steam were pre-heated to the temperature of 700 °C and fed into the reactor. In the third system a fuel sample in the reactor was heated to the temperature 700 °C and the set temperature was maintained with the resistance furnace. The results showed that sufficient thermal energy required for an effective oxygen/steam gasification process was generated in systems with the external heating of the reactor. The highest hydrogen contents in gas were reported in coal gasification, irrespective of the system configuration. The total hydrogen volume decreased with increasing biomass content in a fuel blend in all studied system configurations.

部分開放空間内における水素漏洩挙動の感度解析

To develop a numerical simulation system for leaked hydrogen gas behavior, we compared calculated results by some calculation methods and time histories of hydrogen gas concentration at seven sensor positions of leaking hydrogen gas in a half-size Hallway model experimental test. The calculated results show good agreement with experimental results. Depending on the calculation method, some effect is shown.

Fiber optic hydrogen gas sensor utilizing surface plasmon resonance and native defects of zinc oxide by palladium

We present an experimental study on a surface plasmon resonance (SPR) based fiber optic hydrogen gas sensor employing a palladium doped zinc oxide nanocomposite (ZnO(1−x)Pdx, 0 ≤ x ≤ 0.85) layer over the silver coated unclad core of the fiber. Palladium doped zinc oxide nanocomposites (ZnO(1−x)Pdx) are prepared by a chemical route for different composition ratios and their structural, morphological and hydrogen sensing properties are investigated experimentally. The sensing principle involves the absorption of hydrogen gas by ZnO(1−x)Pdx, altering its dielectric function. The change in the dielectric constant is analyzed in terms of the red shift of the resonance wavelength in the visible region of the electromagnetic spectrum. To check the sensing capability of sensing probes fabricated with varying composition ratio (x) of nanocomposite, the SPR curves are recorded typically for 0% H2 and 4% H2 in N2 atmosphere for each fabricated probe. On changing the concentration of hydrogen gas from 0% to 4%, the red shift in the SPR spectrum confirms the change in dielectric constant of ZnO(1−x)Pdx on exposure to hydrogen gas. It is noted that the shift in the SPR spectrum increases monotonically up to a certain fraction of Pd in zinc oxide, beyond which it starts decreasing. SEM images and the photoluminescence (PL) spectra reveal that Pd dopant atoms substitutionally incorporated into the ZnO lattice profoundly affect its defect levels; this is responsible for the optimal composition of ZnO(1−x)Pdx to sense the hydrogen gas. The sensor is highly selective to hydrogen gas and possesses high sensitivity. Since optical fiber sensing technology is employed along with the SPR technique, the present sensor is capable of remote sensing and online monitoring of hydrogen gas.

Temperature dependent dual hydrogen sensor response of Pd nanoparticle decorated Al doped ZnO surfaces

Sputter deposited Al doped ZnO (AZO) thin films exhibit a dual hydrogen sensing response in the temperature range 40 °C–150 °C after surface modifications with palladium nanoparticles. The unmodified AZO films showed no response in hydrogen in the temperature range 40 °C–150 °C. The operational temperature windows on the low and high temperature sides have been estimated by isolating the semiconductor-to-metal transition temperature zone of the sensor device. The gas response pattern was modeled by considering various adsorption isotherms, which revealed the dominance of heterogeneous adsorption characteristics. The Arrhenius adsorption barrier showed dual variation with change in hydrogen gas concentration on either side of the semiconductor-to-metal transition. A detailed analysis of the hydrogen gas response pattern by considering the changes in nano palladium due to hydrogen adsorption, and semiconductor-to-metal transition of nanocrystalline Al doped ZnO layer due to temperature, along with material characterization studies by glancing incidence X-ray diffraction, atomic force microscopy, and transmission electron microscopy, are presented.

Liquefaction of cotton seed in sub-critical water/ethanol with modified medical stone for bio-oil

This study investigated thermal liquefaction of cotton seed in an autoclave. The effects of solvent (ethanol/water, water and ethanol), temperature and some additives on product distribution were investigated. The results showed that using ethanol/water as solvent could get higher total conversion. The highest liquid oil yield (38.4%) was obtained at 300°C, 2MPa and 30min in ethanol/water with Mo/MS (medical stone). The highest hydrogen content in gas also was obtained when adding Mo/MS, and then followed by that when adding Co–Mo/MS. 1H NMR analysis indicated that the use of additives (except MS) could increase the aliphatic content in liquid oil. 1H NMR and 13C NMR showed that the liquefied oil from liquefaction of cotton seed mainly obtained aliphatic compounds, and adding the additives only changed the amount of compounds and did not alter the type of compounds obtained in the oil.

The growth scale and kinetics of WS2 monolayers under varying H2 concentration.

The optical and electronic properties of tungsten disulfide monolayers (WS2) have been extensively studied in the last few years, yet growth techniques for WS2 remain behind other transition metal dichalcogenides (TMDCs) such as MoS2. Here we demonstrate chemical vapor deposition (CVD) growth of continuous monolayer WS2 films on mm2 scales and elucidate effects related to hydrogen (H2) gas concentration during growth. WS2 crystals were grown by reduction and sulfurization of WO3 using H2 gas and sulfur evaporated from solid sulfur powder. Several different growth formations (in-plane shapes) were observed depending on the concentration of H2. Characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed etching of the SiO2 substrate at low concentrations of H2 and in the presence of an Ar carrier gas. We attribute this to insufficient reduction of WO3 during growth. High H2 concentrations resulted in etching of the grown WS2 crystals after growth. The two dimensional X-ray diffraction (2D XRD) pattern demonstrates that the monolayer WS2 was grown with the (004) plane normal to the substrate, showing that the WS2 conforms to the growth substrate.

Influence of oxygen gas concentration on hydrogen sensing of Pt/WO3 thin film prepared by sol–gel process

High-performance hydrogen gas sensors are needed to ensure safe use of hydrogen gas as a clean energy resource. Pt catalyst-loaded tungsten oxide (Pt/WO3), which shows gasochromism, is an excellent candidate for optical hydrogen gas sensor applications. Pt/WO3 turns blue in a hydrogen gas atmosphere and its electrical conductivity also changes at the same time.This study investigated the influence of partial pressures of hydrogen and oxygen gases on the gasochromism of Pt/WO3. Using elementary gasochromic reactions as a basis, we estimated the concentration of hydrogen injected into a WO3 lattice from the equilibrium of elementary reaction velocities. The estimation suggested that the inverse of the hydrogen concentration in WO3 was inversely proportional to the partial pressure of hydrogen and was proportional to that of oxygen. Additionally, the estimation agreed well with the results of Pt/WO3 gasochromic properties. Therefore, we were able to confirm the dependence of gasochromism on the partial pressures of hydrogen and oxygen gases, and substantiate that Pt/WO3 is capable of detecting hydrogen gas concentrations in various atmosphere conditions where oxygen gas partial pressures change.

Hydrogen gas inhalation protects against liver ischemia/reperfusion injury by activating the NF-κB signaling pathway.

Hydrogen has been demonstrated to function as a novel antioxidant and exert therapeutic antioxidant activity in a number of diseases. The present study was designed to investigate the effect of hydrogen inhalation on liver ischemia/reperfusion (I/R) injury in rats. The portal triad to the left lobe and the left middle lobe of the liver were completely occluded for 90 min. This was followed by reperfusion for 180 min. The rats subsequently underwent syngeneic orthotopic liver transplantation. Inhalation of various concentrations (1, 2 and 3%) of hydrogen gas and its administration for different durations (1, 3 and 6 h) immediately prior to the I/R injury allowed the optimal dose and duration of administration to be determined. Liver injury was evaluated through biochemical and histopathological examinations. The expression levels of proinflammatory cytokines, including tumor necrosis factor (TNF)-α and interleukin (IL)-6, were measured by enzyme-linked immunosorbent assay and quantitative polymerase chain reaction (qPCR). Liver nuclear factor κB (NF-κB) was detected by qPCR and western blot analysis. Inhalation of hydrogen gas at 2% concentration for 1 h significantly reduced the serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, the expression of cytokines, including IL-6, TNF-α, early growth response protein 1 (Egr-1) and IL-1β, and morphological damage. In addition, the mRNA and protein expression levels of NF-κB, heme oxygenase-1 (HO-1), B-cell lymphoma 2 (Bcl-2) and zinc finger protein A20 (A20) in rats where only the donors received hydrogen were significantly increased compared with those in rats where both the donor and recipient, or only the recipient received hydrogen. The results indicate that hydrogen inhalation at 2% concentration for 1 h prior to liver transplantation protected the rats from ischemia/reperfusion injury by activation of the NF-κB signaling pathway.

Surface plasmon resonance-based fiber-optic hydrogen gas sensor utilizing palladium supported zinc oxide multilayers and their nanocomposite.

We analyze surface plasmon resonance-based fiber-optic sensor for sensing of small concentrations of hydrogen gas in the visible region of the electromagnetic spectrum. One of the two probes considered has multilayers of zinc oxide (ZnO) and palladium (Pd) while the other has layer of their composite over a silver coated unclad core of the fiber. The analysis is carried out for different volume fractions of palladium nanoparticles dispersed in zinc oxide host material in the nanocomposite layer. For the analysis, a Maxwell-Garnett model is adopted for calculating the dielectric function of a ZnO:Pd nanocomposite having nanoparticles of dimensions smaller than the wavelength of radiation used. The effects of the volume fraction of the nanoparticles in the nanocomposite and the thickness of the nanocomposite layer on the figure of merit of the sensor have been studied. The film thickness of the layer and the volume fraction of nanoparticles in the ZnO:Pd nanocomposite layer have been optimized to achieve the maximum value of the figure of merit of the sensor. It has been found that the figure of merit of the sensing probe coated with ZnO:Pd nanocomposite is more than twofold of the sensing probe coated with multilayers of Pd and ZnO over a silver coated unclad core of the fiber; hence, the sensor with a nanocomposite layer works better than that with multilayers of zinc oxide and palladium. The sensor can be used for online monitoring and remote sensing of hydrogen gas.

The neutral gas content of post-merger galaxies

Measurements of the neutral hydrogen gas content of a sample of 93 post-merger galaxies are presented, from a combination of matches to the ALFALFA.40 data release and new Arecibo observations. By imposing completeness thresholds identical to that of the ALFALFA survey, and by compiling a mass-, redshift- and environment-matched control sample from the public ALFALFA.40 data release, we calculate gas fraction offsets (Delta f_gas) for the post-mergers, relative to the control sample. We find that the post-mergers have HI gas fractions that are consistent with undisturbed galaxies. However, due to the relative gas richness of the ALFALFA.40 sample, from which we draw our control sample, our measurements of gas fraction enhancements are likely to be conservative lower limits. Combined with comparable gas fraction measurements by Fertig et al. in a sample of galaxy pairs, who also determine gas fraction offsets consistent with zero, we conclude that there is no evidence for significant neutral gas consumption throughout the merger sequence. From a suite of 75 binary merger simulations we confirm that star formation is expected to decrease the post-merger gas fraction by only 0.06 dex, even several Gyr after the merger. Moreover, in addition to the lack of evidence for gas consumption from gas fraction offsets, the observed HI detection fraction in the complete sample of post-mergers is twice as high as the controls, which suggests that the post-merger gas fractions may actually be enhanced. We demonstrate that a gas fraction enhancement in post-mergers, relative to a stellar mass-matched control sample, would indeed be the natural result of merging randomly drawn pairs from a parent population which exhibits a declining gas fraction with increasing stellar mass.