Higher Amount Of Hydrogen Research Articles

Towards the mechanism of electrochemical hydrogen storage in nanostructured carbon materials

The mechanism of electrochemical hydrogen storage in a nanostructured carbon electrode using the electrodecomposition of KOH and H2SO4 aqueous solutions has been investigated by means of galvanostatic and voltammetry techniques. The role of charging the electrical double layer is carefully considered during the process of hydrogen insertion and deinsertion into carbon, i.e. electroreduction and electrooxidation, respectively. Once the electrode potential becomes lower than the equilibrium potential, hydrogen in the zero oxidation state is formed by the reduction of water in alkaline solution or the reduction of hydronium ions H3O+ in acidic medium. In the next step, hydrogen is physically adsorbed (Had) onto the carbon surface and diffuses into the bulk of the carbon material with an efficiency which depends on the type of electrolyte. A higher amount of hydrogen is stored using the KOH medium, and the galvanostatic oxidation shows a well-defined plateau around -0.5 V vs. Normal Hydrogen Electrode (NHE). Due to the high overvoltage value in KOH (η=0.55 V), the recombination steps of Had leading to molecular hydrogen evolution through the chemical (Tafel) or electrochemical (Heyrovsky) reactions are less favoured than in an H2SO4 medium (η=0.32 V). Hence, a meaningful sorption of hydrogen is observed only in the basic electrolyte which shows a reversible capacity of 350 mA h/g (i.e. 1.3 wt. %) with a good electrical efficiency. Such performance demonstrates that nanostructured activated carbons might be a promising alternative to metallic alloys for electrochemical hydrogen storage.

Hydrogen sensor based on optical and electrical switching

We report about a hydrogen sensor using electrical and optical switching properties of Pd-based thin films. Palladium is well known for its ability to absorb high amounts of hydrogen due to palladium hydride formation. Series of different thickness Pd films (10–70 nm) were deposited on glass substrates by dc plasma sputtering. A CaF 2 buffer layer was deposited between the glass support and the Pd-film in order to reduce the internal stresses and improve the mechanical stability of the sensor. A Pt diffusion barrier was deposited on the active film to prevent sensor poisoning. Pd-polymer nano-composite films were deposited by co-sputtering of Pd and polymer targets. The morphology and composition of the films were analysed by SEM, TEM and EDS. Electrical resistance and differential transmittance were measured depending on different concentrations and flows of the testing gas (0.5–10.0% hydrogen in nitrogen). A proportional dependence of the measured signal on the hydrogen concentration was found. The influence of different structures and morphologies on the switching properties was investigated.

Hydrogen Diffusion in Zr-Cu-Ni-Al Metallic Glasses

AbstractZr-based metallic glasses are known to absorb high amounts of hydrogen, but exhibiting less severe embrittlement than their crystalline counterparts; therefore, they might be useful for hydrogen storage application. In order to understand kinetics of hydrogen absorption and desorption in more detail, data on hydrogen diffusion are necessary. The aim of this paper is to present hydrogen diffusivities in melt-spun amorphous Zr69.5Cu12Ni11Al7.5 alloys.Hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. Hydrogen contents were measured by a microbalance with accuracy of ±1 μg as well as by LECO. Diffusivities of hydrogen atoms were measured at different temperatures by the technique of Nuclear Magnetic Resonance (NMR) diffusion in a static fringe field of a superconducting magnet. The diffusion of hydrogen nuclei in an inhomogeneous magnetic field is accompanied by the change of its NMR resonance frequency, which produces motional destruction of the spin echo signal. The analysis of the echo damping allows a model-independent determination of the hydrogen self-diffusion constant, with the low limit of sensitivity D>10−10 cm2/s.Within the temperature interval between room temperature and 420 K diffusivities in the range between 4×10−8 and 1.2×10−9 cm2/s were observed. The Arrhenius-type temperature dependence indicate a simple classical over-barrier-hopping hydrogen diffusion; the activation energy increases slightly with the hydrogen content. Whereas in a number of metallic glasses hydrogen diffusion is known to increase with the hydrogen content, in Zr69.5Ni12Cu11Al7.5 the opposite effect was observed, at least for hydrogen contents between H/M = 0.2 and 1.2. The results will be compared with other measurements known for Zr-based metallic glasses (e.g., Zr-Ni) and discussed in detail, e.g. in regard to the density of the glass.

Pretreatment of Miscanthus for hydrogen production by Thermotoga elfii

Pretreatment methods for the production of fermentable substrates from Miscanthus, a lignocellulosic biomass, were investigated. Results demonstrated an inverse relationship between lignin content and the efficiency of enzymatic hydrolysis of polysaccharides. High delignification values were obtained by the combination of mechanical, i.e. extrusion or milling, and chemical pretreatment (sodium hydroxide). An optimized process consisted of a one-step extrusion-NaOH pretreatment at moderate temperature (70°C). A mass balance of this process in combination with enzymatic hydrolysis showed the following: pretreatment resulted in 77% delignification, a cellulose yield of more than 95% and 44% hydrolysis of hemicellulose. After enzymatic hydrolysis 69% and 38% of the initial cellulose and hemicellulose fraction, respectively, was converted into glucose, xylose and arabinose. Of the initial biomass, 33% was converted into monosaccharides. Normal growth of Thermotoga elfii on hydrolysate was observed and high amounts of hydrogen were produced.

Decrease in activity caused by hydrogen in Ziegler–Natta ethene polymerisation

In this study we prepared seven different Ziegler–Natta catalysts and polymerised them at different hydrogen concentrations in order to investigate their kinetic behaviour during polymerisation. The objective was to see whether the results corresponded to what could be expected on the basis of Kissin's β-agostic deactivation theory. According to this theory, hydrogen causes the formation of dormant sites due to the formation of β-agostic coordination from the ethyl groups formed after hydrogen termination. According to this theory, the more hydrogen that is used, the more β-agostic coupling and the smaller percentage of Ti in a polymerising state. This β-agostic coupling would thus explain the lower activity level seen in polymerisation where more hydrogen has been used. The results of this study showed that none of the catalysts showed the kind of behaviour that would correspond to what could be predicted on the basis of Kissin's theory. Deactivation could be detected only when a lower amount of hydrogen was used. When higher amounts of hydrogen were used in polymerisation there was a clear delay in activation time of the catalysts. This particularly seemed to be the case for catalysts where Ti was present as Ti(IV). This delay in the activation of the catalyst caused a decrease in activity in addition to the normal decrease in activity due to hydrogen replacing C 2 ′′ in the polymerisation process. The only catalyst showing no delay in activation was a silica-based PE ZN catalyst where the Ti was already in trivalent form. In this case no decrease in activity was observed in addition to the normal decrease in activity caused by hydrogen replacing C 2 ′′ in the polymerisation process.

Computer Modeling of Porosity and Lithology for Complex Reservoirs Using Well-Log Measurements

The high degree of heterogeneity, saturation of multiphase fluids, and presence of clays in complex reservoirs make each of the three porosity logs (sonic, density, and neutron), if used independently, generally record inaccurate porosity. For such reservoirs, combining different logs gives accurate results of porosity. The reservoirs of Terra Nova and Hibernia (Jeanne d?Arc Basin), offshore of the eastern coast of Canada, are saturated with multiphase fluids, enriched with clays, and made of compacted and heterogeneous rocks, in terms of the lithological and mineralogical composition, and the size and shape of the grains and pores. In this study, the porosity and the rock constituents were determined for both reservoirs using a computer technique in which the iteration process was applied. That was done by developing and using various computer programs and models, and utilizing numerous data from several logs analyzed at 0.2-m sampling-depth intervals. The more the number of logs and iterations used in computation, the higher the degree of accuracy of results obtained. The reservoirs are made of shalestone, sandstone, siltstone, limestone, marlstone, and conglomerate. The porosity varies widely, because of variations in the rock composition and overburden pressure. The modeled porosity was compared to the porosity measured by the compensated neutron log (CNL). The results indicate that the CNL-measured porosity is generally higher than the modeled porosity by about 50%. The CNL-measurements are greatly affected by the high amount of hydrogen that is chemically bound in the shales, hydrocarbons, and water. Therefore, CNL records higher values of porosity when porosity is actually low, and lower values of porosity when it is actually high.

Innovative devices for hydrogen removal

In case of a severe accident in light water reactors (LWR) a high amount of hydrogen, up to about 20 000 m n 3, might be generated and released into the containment. The mixture, consisting of hydrogen and oxygen, may either burn or detonate, if ignited. In case of detonation the generated shock wave may endanger the integrity of the containment or safety-related systems. Consequently, an effective removal of hydrogen is required. Hydrogen and oxygen react exothermally at catalytically acting surfaces, already at room temperature, and this is used in catalytic recombiners. It is recommended to combine recombiners with spark or catalytic igniters, in order to cover a broader spectrum of accident sequences. In this contribution, state of the art of hydrogen removal devices are reviewed and the possibilities for innovative methods, making use of the phenomena arising in the containments, using further components will be illustrated accordingly.

Storage of reactive hydrogen species in CeMxOy (M = Cu, Ni; 0≤x≤1) mixed oxides

Interaction of hydrogen with a series of mixed oxides CeM x O y (M = Cu, Ni; 0 ⩽ x ⩽ 1) has been studied in the 300–1073 K temperature range. A dynamic method of titration has been used to provide evidence for reactive hydrogen H∗ present in the solids. This method of titration involves hydrogenation at 423 K of isoprene under helium flow in the absence of gaseous hydrogen. The hydrogen reservoir capacity depends on the pretreatment temperature under H 2 and is related to the creation of anionic vacancies in the solid. All the CeM x O y mixed oxides are large catalytic hydrogen reservoirs with marked diffusion properties of hydrogen species (H∗, OH −). In the series studied, the highest amount of hydrogen H∗ (29.5 10 −3 mol g −1) is stored by CeNi 0.7O y pretreated under H 2 at 523 K (H 6.8CeNi 0.7O y ). In the conditions in which the incorporation of hydrogen in the solid occurs, X-ray diffraction analysis under H 2 shows shifts depending on the treatment temperature and corresponding to non-negligeable expansion of the ceria-based lattice attributed to the insertion of hydrogen species of hydridic nature in the anionic vacancies.

Effect of Noble Metal Addition on Electrochemical Polarization Behavior of Hydrogen Oxidation and Oxygen Reduction on Type 304 Stainless Steel in High-Temperature Water

Abstract The effect of noble metal addition on polarization behavior of hydrogen (H2) oxidation and oxygen (O2) reduction on type 304 stainless steel (SS, UNS S30400) in high-temperature, high-purity water was studied. Incorporation of small amounts of noble metals dramatically improved H2 oxidation kinetics and, thus, enhanced the catalytic recombination efficiency of H2 to O2 to form H2O. Enhancement in the catalytic nature on the type 304 SS surface doped with noble metals resulted in the thermodynamically lowest electrochemical corrosion potential (< −500 mVSHE) when a stoichiometric or higher amount of hydrogen was present in the water.

Vacuum-ultraviolet photolysis of polymers

Polyethylene (PE), polypropylene (PP), and poly(ethylene terephthalate) (polyester, PET) were subjected to vacuum-ultraviolet (VUV) radiation from a hydrogen plasma in high vacuum at 10 −8m bar. The residual gas was analysed by mass spectrometry. PE and PP were found to produce high amounts of hydrogen during irradiation. They also formed considerable amounts of hydrocarbons. PP split off its methyl side-group in particular during the first few seconds of irradiation. The species found in the residual gas indicate the formation of double bonds, cross-links and main chain scissions in the polymer surface. PET appeared to be quite stable under VUV irradiation. The only species that was found in the gas phase in significant amounts was carbon dioxide, which came from the destruction of the ester groups.

Effect of impurity hydrogen on the deformation and fracture in an Al-5 mass Pct Mg alloy

Air-melted and argon-melted Al-5 mass pct Mg alloy specimens containing impurity hydrogen of 0.27 and 0.04 mass ppm, respectively, were tensile-tested at ambient temperature. The ductility and fracture processes were compared in the two specimens, and hydrogen evolution behavior during the test was also compared using a special testing machine equipped with a mass spectrometer and ultra high vacuum chamber. The air-melted specimen, containing a higher amount of hydrogen, had less reduction in area (RA) and a higher amount of evolved hydrogen gas on fracture. This implied that the impurity hydrogen was in the transgranular voids, which appeared as dimples on the fracture surface. Fracture process analysis involving fractography, load-displacement curve analysis, and optical microscopy on a cross section of the deformed test piece demonstrated that the impurity hydrogen reduces nonuniform elongation by accelerating the nucleation of transgranular voids produced under triaxial tensile stress after necking. Hydrogen evolution was also detected corresponding to each load drop in the serrated flow of the air-melted specimen, supporting the idea that hydrogen atoms are transported with moving dislocations.

Evaluation and improvement of the energy efficiency of nitrogen fixation in Lotus corniculatus nodules induced by Rhizobium loti strains indigenous to Uruguay

In order to evaluate energy efficiency of nitrogen fixation by the Lotus corniculatus/Rhizobium loti symbiosis, Uruguayan R. loti strains were tested for hydrogen-uptake (Hup) status. Nodules induced in L. corniculatus by all eight R. loti strains tested evolved high amounts of hydrogen (2.0–8.7 μ mol H2/h.g nodule fresh weight). This production of hydrogen corresponds to 38–69% of total nitrogenase activity estimated as acetylene reduction, suggesting that hydrogen is not recycled within these nodules. This was confirmed by the lack of hydrogenase activity in bacteroid suspensions. Additionally, no hybridization signals were observed in total DNA restriction digests from these strains when a DNA fragment containing part of hydrogenase structural genes from Rhizobium leguminosarum bv. viciae was used as probe. Cosmid pHU52, containing the complete gene cluster required for hydrogen oxidation in Bradyrhizobium japonicum, was introduced into two R. loti strains. Transconjugants from only one of the strains were able to express hydrogenase activity in vegetative cells incubated under the derepression conditions described for B. japonicum. Bacteroids induced by both transconjugant strains in L. corniculatus and Lotus tenuis expressed hydrogenase activity in nodules. The level of hydrogenase activity induced in L. tenuis nodules was two-fold higher than those induced in L. corniculatus. This implies the existence of a strong host effect on hydrogenase expression in this symbiotic system.

Effect of incorporation of copper or nickel on hydrogen storage in ceria. Mechanism of reduction

Interaction of hydrogen with a series of mixed oxides CeMx(M = Cu, Ni; 0 < x⩽ 5) precursors of catalysts for hydrogenation reactions has been studied in the 300–1073 K temperature range. In situ XRD, XPS, EPR and thermogravimetric techniques have been used to characterize the processes occurring during the hydrogen treatment, and the amounts of hydrogen occluded in the solids when treated at different temperatures under flowing H2 have also been determined. The most interesting phenomena have been found to occur in the activation temperature range. They involve a non-negligible expansion of the ceria-based lattice which has been attributed to the high amount of hydrogen stored in the host oxide and the reduction of Ce4+ to Ce3+. The M2+ reduction is slowed down, depending on the content of M2+ in the ceria lattice: redox processes between Ce4+, Ce3+, M and M+ or M2+ have been clearly demonstrated. Finally, a reduction mechanism, partly based on heterolytic dissociation of H2, is proposed. This may be extended to bulk mixed oxides with other transition metals, and to a certain extent to metals of Group VIII (Rh, Pd, Ir, Pt) deposited on ceria.

Pre-feasibility analysis of an energy supply system for Southern Europe: Technical aspects

Technical aspects of the feasibility of energy transmission from hydroelectric power plants in Zaire to southern Europe, and to Italy in particular, have been studied. Three alternatives were considered: electric power transmission, gaseous hydrogen pipeline, and methylcyclohexane/toluene loop cycle. The technical feasibility of each alternative, also for a mid-term prospect, and energy losses were examined and evaluated. A comparison, from an energetic point of view, was also carried out among the three systems by varying the ratio between hydrogen and electric power required by the users. The high values of the energy transmission factor make this energy supply system very attractive. Depending on the sharing of the energy required for final uses, a double transportation system, based on electric power together with hydrogen, could be convenient. Indeed, if a very high amount of hydrogen is required by the users, a system based on hydrogen would be preferable.

Sorption of hydrogen and kinetics of hydrogen evolution on amorphous Ni-S x electrodes

Electrolytically prepared Ni-S x layers with a sulphur content ranging between 10 and 20 wt% have a higher activity for the hydrogen evolution reaction (HER) ( j 0 ≌ 2.5–35 × 10 −5 A cm −2) in comparison with nickel electrodes ( j 0 ≅ 1.5 × 10 −5 A cm −2). Ni-S x electrodes sorb high amounts of hydrogen. The greater part of this hydrogen is present in the absorbed hydride form. The thermal treatment of electrodeposited layers (1–4 h at 150°C) causes the decrease in the rate of HER by approximately one order of magnitude and, simultaneously, the decrease in hydrogen sorption. X-ray diffraction analysis showed that Ni-S x layers are originally amorphous but become crystalline after a thermal treatment.

Electrocatalytic protection against hydrogen embrittlement of tantalum in strong acids by platinum ion implantation

As a result of corrosion in strong mineral acids, tantalum takes up high amounts of hydrogen which leads to embrittlement by hydride formation and to mechanical failure. Electrochemical measurements and immersion tests in hot concentrated sulphuric acid show that ion implantation of platinum considerably reduces embrittlement. This is attributed to the strong catalytic activity of platinum which reduces hydrogen adsorption on tantalum and decreases corrosion reactions including hydrogen evolution.

Metopus, Cyclidium and Sonderia: ciliates enriched and cultured from sulfureta of a microbial mat community

Metopus contortus (Class Spirotrichea), Cyclidium borrori, Cyclidium sp., Sonderia tubigula, and two other species of Sonderia (Class Oligohymenophorea) were enriched from the sulfureta of microbial mat communities at Laguna Figueroa near San Quintin, Baja California, Mexico. The ability of some of these species to grow under anaerobic, high-sulfide conditions was demonstrated. The ultrastructural morphology of Metopus and Cyclidium revealed adaptations to anaerobic, high sulfide niches. Metopus lacks typical mitochondria and has structures which may be intracellular bacterial symbionts. Cyclidium borrori, when grown aerobically, has mitochondria with tubular cristae. When it is grown anaerobically in the presence of high amounts of hydrogen sulfide the number of mitochondria remains the same but the mitochondria dedifferentiate, becoming smaller with less well-defined cristae.

Evidence for stronly bonded hydrogen in a Rh/TiO2 catalyst

Thermodesorption of H2 from a Rh/TiO2 catalyst shows that the solid strongly helds a high amount of hydrogen particularly when it is reduced at elevated temperature (773 K). Nevertheless, this residual hydrogen does not seem to be the cause of the unusual chemisorptive properties of the SMSI catalysts.