Hydrogen Gas Concentration Research Articles

Characterization and testing of Pt/TiO2/SiC thin film layered structure for gas sensing

This paper presents the results of our investigations on the gas sensing performance of Pt/TiO2/SiC based field effect devices. The current–voltage characteristics of these Pt/TiO2/SiC sensors at 530°C showed a clear shift to lower voltages upon exposure to increasing hydrogen gas concentration. This indicates a reduction in the metal-oxide interface barrier height, arising from the flattening of the energy bands at the interface and can be attributed to the lowering of the Pt work function due to absorption of hydrogen. The effective change in barrier height Δφb for 1% hydrogen in air was found to be 125meV. The thermal stability of the interfaces in the Pt/TiO2/SiC devices was studied by Rutherford backscattering spectrometry (RBS). The RBS spectra of the sample in as deposited and annealed conditions were compared and analyzed. The Pt/TiO2 and TiO2/SiC layers showed a sharp interface with minimal inter-diffusion. The film composition found to be stable even after repeated testing by exposing to analyte gases. This was further confirmed by X-ray photoelectron spectroscopy analysis of the samples.

The state of P Onb non-bridging oxygen and proton incorporation in binary MO·P2O5 (M = Ca, Mg) phosphate glasses

Abstract Binary x MO·(100 − x )P 2 O 5 (mol%; M = Ca, Mg) glasses were prepared using a conventional melting method, and the proton conduction mechanism in the glasses was investigated. The proton conductivities of the glasses were measured under various hydrogen (H 2 ) gas concentrations from 0 to 100 vol.% using Pt electrodes. The CaO·P 2 O 5 glasses show higher proton conductivities than MgO·P 2 O 5 ones. Fourier-transform infrared (FTIR) measurements showed that protons dissociated from H 2 gas at the Pt electrodes are incorporated into the glasses, and the proton conductivity increases as a result of an increase in the carrier (proton) concentration. There is a good linear relationship between the peak wavenumber of P O nb (O nb indicates non-bridging oxygen) and the proton conductivity measured in a 100 vol.% H 2 atmosphere. Furthermore synchrotron radiation X-ray diffraction (SRXRD) and FTIR results suggest that the π-electron of P O double bond is localized significantly in MgO·P 2 O 5 compared with CaO·P 2 O 5 glasses, which is the origin of higher proton conductivity in CaO·P 2 O 5 glasses.

On the H i column density–radio source size anticorrelation in compact radio sources

Existing studies of the atomic hydrogen gas content in distant galaxies, through the absorption of the 21-cm line, often infer that the total column density is anti-correlated with the linear extent of the background radio source. We investigate this interpretation, by dissecting the various parameters from which the column density is derived, and find that the relationship is driven primarily by the observed optical depth, which, for a given absorber size, is anti-correlated with the linear size. Therefore, the inferred anti-correlation is merely the consequence of geometry, in conjunction with the assumption of a common spin temperature/covering factor ratio for each member of the sample, an assumption for which there is scant observational justification. While geometry can explain the observed correlation, many radio sources comprise two radio lobes and so we model the projected area of a two component emitter intercepted by a foreground absorber. From this, the observed optical depth/linear size relationship is best reproduced through models which approximate either of the two Fanaroff & Riley classifications, although the observed scatter in the sample cannot be duplicated using a single deprojected radio source size. Furthermore, the trend is best reproduced using an absorber of diameter ~100 - 1000 pc, which is also the range of values of linear sizes at which the 21-cm detection rate peaks. This may indicate that this is the characteristic linear size of the absorbing gas structure.

Sensing properties for a microhydrogen sensor with modified palladium film

A microhydrogen gas sensor platform was fabricated by a MEMS process. A nano-bumpy structure was produced using a polystyrene aqueous suspension to develop the surface areas of the sensing area (palladium thin film). The palladium film was deposited on a fabricated platform by a radio frequency magnetron sputtering. A cross section of each AFM image was analyzed to determine the mean surface roughness. The root-mean square roughness of the 1-layer nano-bumpy Pd structure and 2-layers nano-bumpy Pd structure were 9.07nm and 13.1nm, respectively, whereas that of the Pd thin film was 0.98nm. The sensitivities of the Pd thin film sensor, mono-layer nano-bumpy sensor and double-layers nano-bumpy sensor at hydrogen gas concentrations of 2000ppm was 0.638%, 1.045% and 1.511%, respectively.

Proton transport properties of La0.9M0.1YbO3−δ (M = Ba, Sr, Ca, Mg)

The proton transport properties of La0.9M0.1YbO3−δ (M=Ba, Sr, Ca, Mg) were studied by the electrical conductivity measurement technique in the temperature range of 673–1173K. The proton concentration was estimated by the weight changes due to the hydration reaction. The electrical conductivity and proton concentration of La0.9Ba0.1YbO3−δ were the highest in La0.9M0.1YbO3−δ. The electromotive force of a hydrogen gas concentration cell using La0.9Ba0.1YbO3−δ as the electrolyte was observed at 673–1073K, and was in a good agreement with the theoretical values assuming that the proton transport number was unity.

Impact of hydrogen concentrations on the impedance spectroscopic behavior of Pd-sensitized ZnO nanorods

ZnO nanorods were synthesized using a low-cost sol-gel spin coating technique. The synthesized nanorods were consisted of hexagonal phase having c-axis orientation. SEM images reflected perpendicular ZnO nanorods forming bridging network in some areas. The impact of different hydrogen concentrations on the Pd-sensitized ZnO nanorods was investigated using an impedance spectroscopy (IS). The grain boundary resistance (Rgb) significantly contributed to the sensing properties of hydrogen gas. The boundary resistance was decreased from 11.95 to 3.765 kΩ when the hydrogen concentration was increased from 40 to 360 ppm. IS gain curve showed a gain of 6.5 for 360 ppm of hydrogen at room temperature. Nyquist plot showed reduction in real part of impedance at low frequencies on exposure to different concentrations of hydrogen. Circuit equivalency was investigated by placing capacitors and resistors to identify the conduction mechanism according to complex impedance Nyquist plot. Variations in nanorod resistance and capacitance in response to the introduction of various concentrations of hydrogen gas were obtained from the alternating current impedance spectra.

Molecular dynamics simulation of the effect of sub-surface helium bubbles on hydrogen retention in tungsten

Nanometer-sized bubbles in tungsten containing various concentrations of helium and/or hydrogen gas were studied using molecular dynamics simulations. Bubbles of different sizes and compositions were relaxed and evolved at temperatures from 300 K to 2100 K. Helium atoms are evenly distributed inside the bubble at all temperatures, while the hydrogen tends to diffuse to the bubble periphery. In all cases a large amount of hydrogen is bound within the first 1–2 layers of the tungsten matrix surrounding the bubble, though clear dependencies on temperature and bubble composition were found.

Effect of rf power on the structural properties of indium tin oxide thin film prepared for application in hydrogen gas sensor

Indium tin oxide films were grown on glass substrate by rf magnetron sputtering at 648 K. Influence of rf power on structural properties of the ITO films was studied. XRD measurements showed (222) preferred orientation under the optimized deposition conditions. The surface morphology of ITO films analyzed by scanning electron microscope appears to be uniform over the entire surface area, the film exhibited dense layers with fine grains. Finally, ITO sensor device was fabricated and the sensing properties of the device towards hydrogen gas were investigated. The variation in sensitivity of the ITO sensor with operating temperature and with concentration of hydrogen gas was studied. The maximum response was found to be 1.6 at 400 K, for 1,000 ppm of hydrogen gas, and the response of the sensor was found to decrease with increase in concentration of H2 gas.

Bi-layer nanostructures of CuPc and Pd for resistance-type and SAW-type hydrogen gas sensors

Abstract The copper phthalocyanine (CuPc thicknesses ∼80 nm, ∼100 nm and ∼200 nm) covered with ultra thin palladium layer (Pd thickness about 18 nm) has been studied in aspect of their application as bi-layer hydrogen gas-sensing nanostructures. The studies have been performed at low operating temperature range (30–38 °C). The investigated bi-layered structures were obtained by physical vapour deposition under vacuum conditions with application of LiNbO 3 (Y- cut Z-propagating) and glass substrates. Then, the samples were tested by means of the surface acoustic wave and resistance methods. In order to characterize the surface topography the Atomic Force Microscopy has been applied. The characteristic frequency shifts have been observed after exposition to hydrogen. The absolute response value has been found to be dependent on the CuPc film thickness, the interaction temperature, hydrogen gas concentration. Investigations showed also that the bi-layer nanostructure with a 200 nm of CuPc is the most sensitive one. However, at the investigated interaction temperature ∼38 °C, the sensor characteristics are closest to linear dependence for the nanostructure with the 100 nm of CuPc. The simultaneously performed monitoring of the resistance and frequency changes provided observation of the acoustoelectric effect for the investigated nanostructures. The best sensitivity has been observed for the bi-layer structure with 100 nm of CuPc, which is characterized by the acoustoelectric parameter closest to 1.

Fast escape of hydrogen from gas cavities around corroding magnesium implants

Magnesium materials are of increasing interest in the development of biodegradable implants as they exhibit properties that make them promising candidates. However, the formation of gas cavities after implantation of magnesium alloys has been widely reported in the literature. The composition of the gas and the concentration of its components in these cavities are not known as only a few studies using non-specific techniques were done about 60years ago. Currently many researchers assume that these cavities contain primarily hydrogen because it is a product of magnesium corrosion in aqueous media. In order to clearly answer this question we implanted rare earth-containing magnesium alloy disks in mice and determined the concentration of hydrogen gas for up to 10days using an amperometric hydrogen sensor and mass spectrometric measurements. We were able to directly monitor the hydrogen concentration over a period of 10days and show that the gas cavities contained only a low concentration of hydrogen gas, even shortly after formation of the cavities. This means that hydrogen must be exchanged very quickly after implantation. To confirm these results hydrogen gas was directly injected subcutaneously. Most of the hydrogen gas was found to exchange within 1h after injection. Overall, our results disprove the common misbelief that these cavities mainly contain hydrogen and show how quickly this gas is exchanged with the surrounding tissue.

Hydrogen adsorption on and diffusion through MoS2 monolayer: First-principles study

We investigate the hydrogen adsorption on and diffusion through the MoS2 monolayer based on density-functional theory. We show that the hydrogen atom prefers to bond to the S atom at the monolayer, leading to enhanced conductivity. The hydrogen atom can also adsorb at the middle of the hexagon ring by overcoming an energy barrier of 0.57 eV at a strain of 8%. Also, we show that the MoS2 monolayer is flexible and any mechanical deformation of the monolayer is reversible because the extension of the Mo–S bond is much smaller than the applied strain. The monolayer can block the diffusion of hydrogen molecule from one side to the other due to a high energy barrier (6.56 eV). However, the barrier can be reduced to 1.38 eV at a strain of 30% and even totally removed by creating S vacancies and applying a strain of 15%. The MoS2 monolayer may find applications in sensors to detect hydrogen, and as mechanical valve to control the concentration of hydrogen gas.

Electropolymerized Polypyrrole Nanowires for Hydrogen Gas Sensing

In this report, polypyrrole nanowires have been successfully deposited on interdigitated transducers through template-free electropolymerization. The nanowires were 40–90 nm in diameter according to scanning electron microscopy analysis, and some of them were bridging the insulating gaps between gold electrodes. An X-ray photoelectron spectroscopy study has been conducted to determine the chemical composition of the synthesized nanomaterial. The developed sensors were tested toward five concentrations of hydrogen gas at room temperature, and their sensitivities were compared. Due to the very high surface area of the deposited sensitive films, these sensors provided faster response compared to other polypyrrole-based gas sensors. Moreover, it is shown that the sensors’ sensitivities are related to the amount of the deposited PPY nanowires.

Les cicatrices chéloïdes : difficultés thérapeutiques

We investigate the hydrogen adsorption on and diffusion through the MoS2 monolayer based on density-functional theory. We show that the hydrogen atom prefers to bond to the S atom at the monolayer, leading to enhanced conductivity. The hydrogen atom can also adsorb at the middle of the hexagon ring by overcoming an energy barrier of 0.57 eV at a strain of 8%. Also, we show that the MoS2 monolayer is flexible and any mechanical deformation of the monolayer is reversible because the extension of the Mo–S bond is much smaller than the applied strain. The monolayer can block the diffusion of hydrogen molecule from one side to the other due to a high energy barrier (6.56 eV). However, the barrier can be reduced to 1.38 eV at a strain of 30% and even totally removed by creating S vacancies and applying a strain of 15%. The MoS2 monolayer may find applications in sensors to detect hydrogen, and as mechanical valve to control the concentration of hydrogen gas.

Electrochemical property of proton-conductive manganese dioxide for sensoring hydrogen gas concentration

A high-purity, ramsdellite-crystal type manganese dioxide (Koyanaka et al., 2005 [1]; Iikubo et al., 2010 [2]) was used for an electrolyte in a hydrogen gas sensor (Ueda et al., 2011 [3]). In this report, the electrochemical properties of the hydrogen gas sensor using electrolytes made of different crystal types of manganese dioxides, such as the ramsdellite-crystal type, a β-crystal type, and a λ-crystal type were examined. The high-purity, ramsdellite-crystal type manganese dioxide showed the conductivity from 7.1×10−5S/cm (80°C) to 1.7×10−4S/cm (25°C) under 85% relative humidity condition. This conductivity was probably based on the proton conduction on the MnO2 particles.

Conductometric H<sub>2</sub> Gas Sensor With Doped And Dedoped Electropolymerized Polyaniline Nanostructures

Dalam kertas kerja ini, struktur dan prestasi pengesanan gas oleh polianilin yang berskala nano yang dimendap di atas transduser lithium tantalate. Polimer berkonduksi ini disintesiskan melalui teknik electropolymerization. Struktur permukaan polianilin dicirikan dengan menggunakan Mikroskop Pengesan Elektron (Scanning Electron Microscopy). Didapati bahawa polianiline yang terhasil dipermukaan transducer adalah 3–dimensi struktur dan poros. Pengesan ini kemudian disiasat prestasinya terhadap konsentrasi gas yang berbeza dan berada dalam keadaan suhu bilik. Kata kunci: Pengesan H2; polianilin, berskala nano; electropolymerization; dop dan nyah–dop In this work, the structural and gas sensing properties of polyaniline nanostructures deposited on 36° lithium tantalite (LiTaO3) conductometric transducers was investigated. The polyaniline nanostructures were synthesized via an electropolymerization method. The morphology of the nanostructured polyaniline was characterized using Scanning Electron Microscopy (SEM). It was observed that the electropolymerised film was a three–dimensional (3D) porous structure of polyaniline fibers and nanotips. The conductometric sensors were exposed to different concentrations of hydrogen (H2) gas at room temperature. Key words: H2 sensor; polyaniline; nanostructures; electropolymerization; doped and dedoped

Hydrogen gas-sensing properties of Pt/WO3 thin film in various measurement conditions

A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO3). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO3 thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO3 thin films prepared at 400 °C showed the largest change in optical transmittance and electrical conductivity when exposed to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance of W5+ in the thin films depend on the equilibrium reaction between injection and rejection of H+ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations.

Computational Studies for Reduced Graphene Oxide in Hydrogen-Rich Environment

We employ molecular dynamic simulations to study the reduction process of graphene oxide (GO) in a chemically active environment enriched with hydrogen. We examine the concentration and pressure of hydrogen gas as a function of temperature in which abstraction of oxygen is possible with minimum damage to C-sp(2) bonds, hence preserving the integrity of the graphene sheet. Through these studies we find chemical pathways that demonstrate beneficiary mechanisms for the quality of graphene including formation of water as well as suppression of carbonyl pair holes in favor of hydroxyl and epoxide formation facilitated by hydrogen gas in the environment.

Gasochromic and electrical properties of Pt-nanoparticle-dispersed tungsten oxide thin films prepared by a sol-gel process

ABSTRACTIt is well known that tungsten tri-oxide (WO3) exhibits electrochromic and gasochromic properties. When Pt-nanoparticle-dispersed tungsten oxide (Pt-WO3) is exposed to hydrogen gas, the optical and electrical properties of the Pt-WO3 change drastically. Consequently, it is expected that thin films of WO3 can be applied as hydrogen gas leakage sensors. In this study, thin films of Pt-WO3 were prepared on glass substrates using a sol-gel process. The optical and electrical properties of the films were evaluated. Amorphous and crystalline WO3 were easily obtained by changing the heat-treatment temperature. The ion diffusion coefficient of the film depended on the WO3 structure (i.e., whether it was amorphous or crystalline) because the density of amorphous WO3 is lower than that of crystalline WO3. Films with low crystallinity were found to have superior chromic properties to both those with high crystallinity and amorphous films. Thin films of Pt-WO3 prepared at 673K showed the largest change in optical transmittance and electrical conductivity when exposed to H2 gas compared with thin films prepared at other temperatures. When this film was exposed to 100% H2 gas, the normalized transmittance decreased rapidly (in less than 0.2 sec) from 100% to almost 50%. The optical absorbance of the film was dependent on the H2 gas concentration (mixed with N2 gas) in the range from 0.1 to 5% and the relationship between them was linear. The relationship between the electrical conductivity and hydrogen gas concentration (mixed with N2 gas) in the range from 100 to 10000ppm was also linear.

A convenient method for determining the concentration of hydrogen in water: use of methylene blue with colloidal platinum

A simple titration (oxidimetry) method using a methylene blue-platinum colloid reagent is effective in determining the concentration of hydrogen gas in an aqueous solution. The method performs as effectively as the more complex and expensive electrochemical method.

Changes in Work Function and Electrical Resistance of Pt Thin Films in the Presence of Hydrogen Gas

The changes in the electrical properties, such as work function and resistance, of Pt thin films in the presence of hydrogen gas were studied. They were simultaneously measured with a flow-through cell at different concentrations of hydrogen gas in atmosphere containing gaseous nitrogen and that containing air. The resistance was measured by a four-terminal sensing method and the relative work function changes were measured using a field effect transistor. In both atmospheres, the resistance decreased as the concentration of hydrogen gas increased. This result was repeatable only in air because of the differences in the dynamic mechanism of increased density of electrical carriers inside the Pt film as a result of diffused H atoms. In the nitrogen atmosphere, the diffused H atoms were not easily released because of the surface barrier. On the other hand, oxygen gas reacted with H atoms at the surface and this reaction accelerated atom release into air. The work function showed repeatable responses in both atmospheres, but the response characteristics were different. The equilibrium reaction between the adsorption and desorption of hydrogen occurred at the surface in the nitrogen atmosphere, whereas the equilibrium reaction of hydrogen and oxygen to form water molecules occurred in air. The changes in work function and resistance in the presence of hydrogen were due to changes in dissociated hydrogen intensity in the bulk, as well as to the surface reactions.