Wide Range Of Hydrogen Concentrations Research Articles

Preparation and Hydrogen-Sensitive Property of WO3/Graphene/Pd Ternary Composite

Hydrogen (H2) is a renewable energy source that has the potential to reduce greenhouse gas emissions. However, H2 is also highly flammable and explosive, requiring sensitive and safe sensors for its detection. This work presents the synthesis and characterization of WO3/graphene binary and WO3/graphene/Pd (WG-Pd) ternary nanocomposites with varying graphene and Pd contents using the microwave-assisted hydrothermal method. The excellent catalytic efficacy of Pd nanoparticles facilitated the disintegration of hydrogen molecules into hydrogen atoms with heightened activity, consequently improving the gas-sensing properties of the material. Furthermore, the incorporation of graphene, possessing high conductivity, serves to augment the mobility of charge carriers within the ternary materials, thereby expediting the response/recovery rates of gas sensors. Both graphene and Pd nanoparticles, with work functions distinct from WO3, engender the formation of a heterojunction at the interface of these diverse materials. This enhances the efficacy of electron–hole pair separation and further amplifies the gas-sensing performance of the ternary materials. Consequently, the WG-Pd based sensors exhibited the best gas-sensing performance when compared to anther materials, such as a wide range of hydrogen concentrations (0.05–4 vol.%), a short response time and a good selectivity below 100 °C, even at room temperature. This result indicates that WG-Pd ternary materials are a promising room-temperature hydrogen-sensing materials for H2 detection.

Passive electrochemical hydrogen recombiner for hydrogen safety systems: prospects

This paper presents the concept of a passive electrochemical hydrogen recombiner (PEHR). The reaction energy of the recombination of hydrogen and oxygen is used as a source of electrical energy according to the operating principle for hydrogen fuel cells to establish forced circulation of the hydrogen mixture as an alternative to natural circulation (as is not utilized in conventional passive autocatalytic hydrogen recombiners currently used in nuclear power plants (NPPs)). The proposed concept of applying the physical operation principles of a PEHR based on a fuel cell simultaneously increases both productivity in terms of recombined hydrogen and the concentration threshold of flameless operation (the ‘ignition’ limit). Thus, it is possible to reliably ensure the hydrogen explosion safety of NPPs under all conditions, including beyond-design accidents. An experimental setup was assembled to test a laboratory sample of a membrane electrode assembly (MEA) at various hydrogen concentrations near the catalytic surfaces of the electrodes, and the corresponding current–voltage characteristics were recorded. The simplest MEA based on the Advent P1100W PBI membrane demonstrated stable performance (delivery of electrical power) over a wide range of hydrogen concentrations.

Chemical inhibition of hydrogen-air explosions: Literature review, simulations and experiments

This paper summarises the first results from the joint industry project (JIP) ‘Risk-reduction for hydrogen installations by partial suppression of explosions’ (HyRISE). The main objective of the project is to develop fundamental knowledge that can support the development of practical solutions for mitigating hydrogen explosions in congested and confined environments by means of active systems for chemical inhibition. The aim is not to extinguish the incipient flame, but rather to lower the reactivity of the fuel-air mixture prior to ignition, and thereby reduce the consequences of an accidental explosion to a tolerable level. The paper consists of three parts: a review of previous work on chemical inhibition of premixed hydrogen-air flames, simulations with the chemical kinetics software Cantera, and experiments conducted in a 20-litre explosion vessel. The results demonstrate that chemical inhibition can be effective for hydrogen-air mixtures. However, it remains to develop efficient inhibitors and practical systems that can be implemented in industrial facilities, with satisfactory performance over a wide range of hydrogen concentrations.

Flame propagation regimes and critical conditions for flame acceleration and detonation transition for hydrogen-air mixtures at cryogenic temperatures

A series of more than 100 experiments with hydrogen-air mixtures have been performed at cryogenic temperatures from 90 to 130 K and ambient pressure. A wide range of hydrogen concentrations from 8 to 60%H2 in a shock tube of 5-m long and 54 mm id was tested. Flame propagation regimes were investigated for all hydrogen compositions at three different blockage ratios 0, 30% and 60% as a function of initial temperature. Piezoelectric pressure sensors and InGaAs photo-diodes have been applied to monitor the flame and shock propagation velocity of the combustion process. More than 150 experiments at ambient pressure and temperature were conducted as the reference data for cryogenic experiments. The critical expansion ratio σ∗ for an effective flame acceleration to the speed of sound was experimentally found at cryogenic temperatures. The detonability criteria for smooth and obstructed channels were used to evaluate the detonation cell sizes at cryogenic temperatures as well. The main peculiarities of cryogenic combustion with respect to the safety assessment were that the maximum combustion pressure was several times higher and the run-up-distance to detonation was two times shorter compared to ambient temperature independent of lower chemical reactivity at cryogenic conditions.

Magneto-Electronic Hydrogen Gas Sensors: A Critical Review

Devices enabling early detection of low concentrations of leaking hydrogen and precision measurements in a wide range of hydrogen concentrations in hydrogen storage systems are essential for the mass-production of fuel-cell vehicles and, more broadly, for the transition to the hydrogen economy. Whereas several competing sensor technologies are potentially suitable for this role, ultra-low fire-hazard, contactless and technically simple magneto-electronic sensors stand apart because they have been able to detect the presence of hydrogen gas in a range of hydrogen concentrations from 0.06% to 100% at atmospheric pressure with the response time approaching the industry gold standard of one second. This new kind of hydrogen sensors is the subject of this review article, where we inform academic physics, chemistry, material science and engineering communities as well as industry researchers about the recent developments in the field of magneto-electronic hydrogen sensors, including those based on magneto-optical Kerr effect, anomalous Hall effect and Ferromagnetic Resonance with a special focus on Ferromagnetic Resonance (FMR)-based devices. In particular, we present the physical foundations of magneto-electronic hydrogen sensors and we critically overview their advantages and disadvantages for applications in the vital areas of the safety of hydrogen-powered cars and hydrogen fuelling stations as well as hydrogen concentration meters, including those operating directly inside hydrogen-fuelled fuel cells. We believe that this review will be of interest to a broad readership, also facilitating the translation of research results into policy and practice.

Hydrate-based separation of the CO2 + H2 mixtures. Phase equilibria with isopropanol aqueous solutions and hydrogen solubility in CO2 hydrate

The gas hydrates' ability to preferentially bind one of the components of a gas mixture into a hydrate state makes it possible to consider hydrate-based technology as promising for the separation of gas mixtures. When a hydrate is obtained from a gas mixture, mixed hydrates with a complex composition inevitably occur. Issue of their composition determination stays apart. This a rather difficult task, which is complicated by the dissolution of small molecules such as hydrogen in the hydrate phase. This, in turn, impedes the analysis of the data obtained. In this work, the solubility of hydrogen in carbon dioxide hydrate in the range of 269.7–275.7 K and at partial H2 pressure up to 4.5 MPa was experimentally determined. Hydrate composition was found to be CO2·(0.01X)H2·6.5H2O at H2 pressure of X MPa. The equilibrium conditions of hydrates formation in the systems of H2O – CO2 – H2 and H2O – 2-propanol – CO2 – H2 were also determined in a wide range of hydrogen concentrations. Hydrogen seems to be an indifferent diluent gas regarding CO2 hydrate equilibrium pressure. The compositions of the equilibrium phases have been determined as well. It was shown that isopropanol does not form a double hydrate with СО2, only sI СО2 hydrate occurred in the studied systems. The obtained dependencies will be useful in analyzing the process of СО2 + Н2 gas mixtures separation by the hydrate-based method.

РАСЧЕТ ПАРАМЕТРОВ ГАЗОВОЙ СРЕДЫ В КОНТЕЙНМЕНТЕ АЭС С УЧЕТОМ ПОЛНОГО АДИАБАТИЧЕСКОГО СГОРАНИЯ ВОДОРОДА КОДОМ КУПОЛ-М

An important factor for the analysis of hydrogen safety is to take into account the effect of possible hydrogen combustion on the parameters of NPP containment atmosphere. In order to evaluate this effect a model of adiabatic isochoric complete combustion (AICC) of hydrogen was developed and implemented in the KUPOL-M containment code. With the model of adiabatic isochoric complete combustion of hydrogen included in the KUPOL-M code, this code will become applicable for the VVER NPP safety analysis performed with the aim to estimate possible thermal mechanical loads on the containment in case of hydrogen burning. This model is simple, conservative and based on the laws of conservation of mass and energy. The following assumptions are made in the model of adiabatic isochoric complete combustion of hydrogen: the volume in which burning takes place is constant; there is no heat transfer; the limiting component (in most cases it is hydrogen) burns down completely; intermediate stages of chemical transformations are not considered. The test results of this model on experimental data are presented in the article. There is a good agreement between the data of calculations and experiments in a wide range of hydrogen concentrations in gas mixtures. Based on the test results it can be concluded that implementation of AICC model in the KUPOL-M code allows conservatively evaluating the parameters in the containment atmosphere without significantly increasing the calculation time.

Facile synthesis of Al–Mg co-doped ZnO nanoparticles and their high hydrogen sensing performances

Recently hydrogen has received a great attention as a renewable, clean and high-efficiency source of energy. However, its high explosiveness and leakage increased demand for sensors to monitor hydrogen during production, transport, storage and use. This paper presents a new nanostructured material for hydrogen monitoring. Indeed, to our knowledge, the aluminum/magnesium co-doped ZnO nanoparticles are used in the first time for hydrogen sensing. Al(5%)-Mg(1,3,5%) co-doped ZnO nanoparticles were effectively synthesized by facile sol-gel method in supercritical conditions. The structural, morphological and optical properties have been examined by different techniques. X-ray diffraction data confirmed the hexagonal wurtzite structure and showed a good enhancement of crystallinity with introduction of Al and Mg dopants. Transmission electron microscopy observations showed the nanometric size of the nanoparticles (15–25 nm) and the prismatic like shape of the crystallites. The TGA study proves the stability of the samples and the BET analysis illustrate that the isotherm of the 5A1MZO sample is belong to type II. Ultraviolet–Visible spectroscopy measurements evidenced the narrowing of the band gap energy for the co-doped samples which range between 3.14 and 3.19 eV. Photoluminescence spectra of all samples consist of two major components: a narrow ultraviolet emission band and a broad visible emission band (above 500 nm). Electrical properties were also studied. The synthesized samples have been screen printed and investigated as active layer for conductometric gas sensor devices. Their sensing characteristics towards wide range of hydrogen concentrations (100–30,000 ppm) were tested at various temperatures ranging from 200 to 400 °C in dry air. The Al(5%)-Mg(1%) co-doped ZnO sensor displayed the best sensing performances, showing a fast (3 s) and high (larger than 70) response towards 2000 ppm hydrogen at 250 °C. In addition, it showed low detection limit, good repeatability and high selectivity against various interfering gases. Compared to others recent works, the sensor showed competitive performances and by considering the facile, fast and low cost synthesized method of nanoparticles, it represents a promising material for the selective detection of hydrogen.

Quantitative Analysis of Hydrogen in High-Hydrogen-Content Material of Magnesium Hydride via Laser-Induced Breakdown Spectroscopy.

An analytical approach that can rapidly determine a wide range of hydrogen concentration in solid-state materials has been recently demanded to contribute to the hydrogen economy. This study presents a method for estimating hydrogen concentrations ranging from 0.2 to 7.6 mass % via laser-induced breakdown spectroscopy (LIBS) in a few seconds, with an improvement in the upper limit of determination (7.6 mass %) by approximately 1.3 times compared with a previous work (5.7 mass %). This extension of the determinable concentration range was achieved by measuring the emission intensity at 656.28 nm from the sample in a helium atmosphere at 3000 Pa under focused laser irradiation and by reducing the water residues in both the sample and gas line of the LIBS system. The as-determined hydrogen concentrations in magnesium hydride (MgH2) samples agreed well with those estimated through inert gas fusion/gas chromatography. The calibration curve for LIBS analysis was acquired by measuring the emission intensity at 656.28 nm of standard Mg/MgH2 mixtures containing various hydrogen concentrations (0, 0.1, 0.2, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 7.6 mass %). Results indicated that the proposed LIBS-based method is applicable to the rapid quantitative analysis of hydrogen in hydrogen-containing material of MgH2.

Comparison of the Effects of Environmental Treatments on Hydrogen Concentration and Energy Gap Variations of Hydrogenated Amorphous and Polymorphous Silicon Films Prepared by PECVD Technique

Hydrogen to silicon (Si–H) bond concentration and strength play important roles in high quality hydrogenated amorphous silicon layers prepared by PECVD techniques. In this paper, a number of amorphous and polymorphous Si layers have been deposited at different plasma conditions where a wide range of hydrogen concentration in the films are obtained. Some of the samples were stored in free air and the others in nitrogen for eight days. The layers were analyzed using AFM, FTIR, Raman, UV–Visible, and TEM immediately after deposition and after treatments. The results indicate that in the amorphous films with appreciable amount of embedded silicon nanocrystals, the variation of hydrogen content behaves differently than that of the amorphous films. It has been observed that treatment in the air increases the energy gap of the nanocrystals surrounded by oxide shells, formed around the surface nanocrystals, due to the quantum confinement effects.

First-principles study of magnetism, lattice dynamics, and superconductivity in LaFeSiHx

The structural, electronic, magnetic, and vibrational properties of LaFeSiH$_x$ for $x$ between 0 and 1 are investigated using density functional calculations. We find that the electronic and magnetic properties are strongly controlled by the hydrogen concentration $x$ in LaFeSiH$_x$. While fully hydrogenated LaFeSiH has a striped antiferromagnetic ground state, the underdoped LaFeSiH$_x$ for $x\leq0.75$ is not magnetic within the virtual crystal approximation or with explicit doping of supercells. The antiferromagnetic configuration breaks the symmetry of Fe $d$ orbitals and increases electron-phonon coupling up to $50\%$, especially for modes in the 20-50 meV range that are associated with Fe atomic movement. We find competing nearest and next-nearest neighbor exchange interactions and significant spin-phonon coupling, qualitatively similar but smaller in magnitude compared those found in LaOFeAs superconductors. The superconducting $T_c$ for antiferromagnetic LaFeSiH$_x$, assuming conventional superconductivity via McMillan's equation, therefore is computed to be 2-10 K, in contrast to $T_c\approx0$ for the nonmagnetic material. We also predict that the LaFeSiH$_x$ could be a good proton conductor due to phase stability with a wide range of hydrogen concentration $x < 1$.

Tungsten Oxide Photonic Crystals as Optical Transducer for Gas Sensing.

Some metal oxide semiconductors, such as tungsten trioxide or tin dioxide, are well-known as resistive transducers for gas sensing and offer high sensitivities down to the part per billion level. Electrical signal read-out, however, limits the information obtained on the electronic properties of metal oxides to a certain frequency range and its application because of the required electrical contacts. Therefore, a novel approach for building an optical transducer for gas reactions utilizing metal oxide photonic crystals is presented here. By the rational design of the structure and composition it is possible to synthesize a functional material which allows one to obtain insight into its electronic properties in the optical frequency range with simple experimental measures. The concept is demonstrated by tungsten trioxide inverse opal structure as optical transducer material for hydrogen sensing. The sensing behavior is analyzed in a temperature range from room temperature to 500 °C and in a wide hydrogen concentration range (3000 ppm to 10%). The sensing mechanism is mainly the refractive index change resulting from hydrogen intercalation in tungsten trioxide, but the back reaction has also impact on the optical properties of this system. Detailed chemical reaction studies provide suggestions for specific sensing conditions.

Hydrogen gas sensor of Pd‐functionalised AlGaN/GaN heterostructure with high sensitivity and low‐power consumption

A Pd-functionalised hydrogen gas sensor based on an AlGaN/GaN heterostruture platform was investigated. The optimum bias voltage and reaction temperature were 0.1 V and 200°C, respectively, with which a wide range of hydrogen concentration from 0.1-4% in the air (i.e. 1000-40,000 ppm) was detectable. Not only low-power consumption but also high sensitivity with fast response was achieved due to the excellent properties of the AlGaN/GaN heterostructure platform. The sensitivity was 72.8% with a response time of ~3 s in 4% hydrogen concentration.

Gas-phase hydrogenation influence on defect behavior in titanium-based hydrogen-storage material

Titanium and its alloys are promising materials for hydrogen storage. However, hydrogen penetration accompanies the exploitation of hydrogen storage alloys. In particular, hydrogen penetration and accumulation in titanium alloys changes their mechanical properties. Therefore, the research works of such materials are mainly focused on improving the reversibility of hydrogen absorption-liberation processes, increasing the thermodynamic characteristics of the alloys, and augmenting their hydrogen storage capacity. In the process of hydrogenation-dehydrogenation, the formed defects both significantly reduce hydrogen storage capacity and can also be used to create effective traps for hydrogen. Therefore, the investigation of hydrogen interaction with structural defects in titanium and its alloys is very important. The present work, the hydrogen-induced formation of defects in the alloys of commercially pure titanium under temperature gas-phase hydrogenation (873K) has studied by positron lifetime spectroscopy and Doppler broadening spectroscopy. Based on the evolution of positron annihilation parameters τf, τd, their corresponding intensities If, Id and relative changes of parameters S/S0 and W/W0, the peculiarities of hydrogen interaction with titanium lattice defects were investigated in a wide range of hydrogen concentrations from 0.8at% to 32.0at%.

Electrochemical Hydrogen Permeation Tests under Conventional Potentiostatic Hydrogen Charging Conditions Conventionally Used for Hydrogen Embrittlement Study

Electrochemical hydrogen permeation tests were carried out under potentiostatic hydrogen charging conditions in various solutions, and the hydrogen entry behavior was compared with that of galvanostatic method. The relationship between hydrogen permeation current density and potential was similar in potentiostatic and galvanostatic methods and wide range of hydrogen concentration could be covered as well as galvanostatic method by varying NH4SCN content and potential. However, slight differences in hydrogen permeation current density and efficiency of hydrogen entry were seen between the methods, and the stability of hydrogen entry of potentiostatic method was slightly higher than that of galvanostatic method. In both methods, hydrogen permeation current density tended to increase with time in a NH4SCN containing solution suggesting that it is recommended to measure resulted hydrogen content by means of thermal desorption analysis for accuracy, though the relationship between hydrogen permeation current density and potential can be used as a rough standard.

An analysis of flame instabilities for hydrogen–air mixtures based on Sivashinsky equation

In this paper flame instabilities are analyzed utilizing the Sivashinsky equation in order to derive the flame wrinkling factor. This is a synthetic variable representing the excess of flame surface which is obtained for a wide range of hydrogen concentrations, considering the Darrieus–Landau and the Thermo-Diffusive instabilities, and also taking into account the effect of acceleration. Additionally, the time for the development of the cellularity is also analyzed. The study is carried out for a wide range of hydrogen–air mixtures as well as for a large domain of accelerations. Models representing both the wrinkling factor and the time of development of the instabilities are obtained.

Conductometric Sensing of H&lt;sub&gt;2&lt;/sub&gt; by Chromium Niobate

Investigations on chromium niobate (CrNbO4) have shown that the material responds to a wide hydrogen concentration range of 0.01%-0.40% at 613 K. The conductivity of CrNbO4 is independent of oxygen partial pressure and offers to be a promising candidate for monitoring H-2 in radioactive spent fuel storage facilities. Reduction of metal ions to lower valence states during hydrogen sensing was evidenced by X-ray photoelectron spectroscopic studies.

Formation of palladium hydrides in low temperature Ar/H2-plasma

20nm thick Pd coatings deposited on Si substrates with 800nm SiO2 and 1nm Cr buffer layers were treated in a 2.45GHz microwave plasma source at 700W plasma power and 40Pa working pressure without substrate heating. For obtaining information on the effect of energy influx due to ion energy on the palladium films the substrate potential was varied from Usub=0V to −150V at constant gas flow corresponding to mean ion energies Ei from 0.22eV∙cm−2∙s−1 to 1.28eV∙cm−2∙s−1.In contrast to high pressure reactions with metallic Pd, under plasma exposure we do not observe solid solutions over a wide range of hydrogen concentration. The hydrogen incorporation in Pd films takes place discontinuously. At 0V substrate voltage palladium hydride is formed in two steps to PdH0.14 and PdH0.57. At −50V substrate voltage PdH0.57 is formed directly. However, substrate voltages of −100V and −150V cause shrinking of the unit cell. We postulate the formation of two fcc vacancy palladium hydride clusters PdHVac(I) and PdHVac(II). Under longtime plasma exposure the fcc PdHVac(II) phase forms cubic PdH1.33.The fcc PdH0.57 phase decomposes at temperatures >300°C to form metallic fcc Pd. The hydrogen removal causes a decrease of lattice defects. In situ high temperature diffractometry measurements also confirm the existence of PdHVac(II) as a palladium hydride phase. Stoichiometric relationship between cubic PdH1.33 and fcc PdHVac(II) becomes evident from XR measurements and structure considerations. We assume both phases have the chemical composition Pd3H4. Up to 700°C we observe phase transformation between both the fcc PdHVac(II) and cubic PdH1.33 phases. These phase transformations could be explained analog to a Bain distortion by displacive solid state structural changes.

EFFECTS OF OBSTACLES ON PREMIXED HYDROGEN-AIR MIXTURES EXPLOSION IN CLOSED PIPE

Results of experiments on explosion premixed hydrogen-air are presented. The data covers a wide range of hydrogen concentration between 13 to 54 % v/v (Ф= 0.4 to 1.8). The experimental work was performed in a closed pipe containing 90 degree bends with a volume of 0.42 m3operating at ambient conditions. This study was carried out to determine the severity of hydrogen explosion in a closed pipe with length over diameter (L/D) ratio of 51. The results indicate that the worst case accident for hydrogen-air mixture occur at concentration slightly above stoichiometric (Ф 1.2) or 36% v/v. It is also found that pressure downstream the bending region experienced an increase of about 2 times, compared to pressure at the bend. It can be said that a strong backflow or retonation reflecting from the end pipe wall influentthe maximum overpressure downstreamof the bend and this phenomenon was highlighted.

Fast, quantitative, and nondestructive evaluation of hydrided LWR fuel cladding by small angle incoherent neutron scattering of hydrogen

A nondestructive neutron scattering method to precisely measure the uptake of hydrogen and the distribution of hydride precipitates in light water reactor (LWR) fuel cladding was developed. Zircaloy-4 cladding used in commercial LWRs was used to produce hydrided specimens. The hydriding apparatus consists of a closed stainless-steel vessel that contains Zr alloy specimens and hydrogen gas. Following hydrogen charging, the hydrogen content of the hydrided specimens was measured using the vacuum hot extraction method, by which the samples with desired hydrogen concentrations were selected for the neutron study. Optical microscopy shows that our hydriding procedure results in uniform distribution of circumferential hydrides across the wall thickness. Small angle neutron incoherent scattering was performed in the High Flux Isotope Reactor at Oak Ridge National Laboratory. Our study demonstrates that the hydrogen in commercial Zircaloy-4 cladding can be measured very accurately in minutes by this nondestructive method over a wide range of hydrogen concentrations from a very small amount (≈20ppm) to over 1000ppm. The hydrogen distribution in a tube sample was obtained by scaling the neutron scattering rate with a factor determined by a calibration process using standard, destructive direct chemical analysis methods on the specimens. This scale factor can be used in future tests with unknown hydrogen concentrations, thus providing a nondestructive method for determining absolute hydrogen concentrations.