Increase In Hydrogen Uptake Research Articles

Sulphide‐induced stress corrosion cracking and hydrogen absorption of copper in deoxygenated water at 90°C

AbstractStress corrosion cracking (SCC) of oxygen‐free phosphorous‐alloyed copper was investigated in sulphide‐ and chloride‐containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low sulphide environment, where only slight corrosion on grain boundaries and slip lines occurred. Hydrogen content measurements show an increase in hydrogen uptake of the plastically deformed specimens, which is dependent on the sulphide concentration and on plastic deformation of copper. However, the highest hydrogen content was measured in friction stir welds, welded in air without shielding gas, and tested in the high sulphide environment. The embedded oxide particles in the weld metal act as local hydrogen trapping sites and selectively react with the sulphide solution. A relatively thick air‐formed oxide film covers the copper canisters when deposited, which transforms into a sulphide film in the repository conditions. Thus, some of the coupon specimens were pre‐oxidised. The conversion of the pre‐existing Cu2O film into Cu2S film occurs quickly and the transformation is almost 100% efficient. The structure and properties of the Cu2S films, susceptibility of copper to sulphide‐induced SCC and hydrogen uptake of copper in reducing, anoxic repository conditions are discussed.

Evaluation of surface changes at the interface between TiO2 nanoparticles and COOH-MWCNTs on hydrogen adsorption capability

The hydrogen sorption capability of TiO2/COOH-MWCNTs has been examined at 253 K, 298 K and 70 bar pressure. To facilitate the hydrogen adsorption/desorption by TiO2/COOH-MWCNTs, experimental conditions have been optimized by altering metal concentration and solvents (Water, Amine and Dimethyl formamide (DMF)). Morphology and structure were characterized by SEM, TEM and XRD. The adsorption isotherm reveals that the hydrogen uptake capacity of TiO2/COOH-MWCNTs synthesized at different experimental conditions was 0.67 wt% (Water), 0.87 wt% (Amine) and 1.35 wt% (DMF) at 253 K temperature and 70 bar pressure. A 2–3 fold increase in hydrogen uptake was observed at 253 K compared to 298 K in all samples. Furthermore, a substantial increase in hydrogen uptake capacity (4 fold) was observed compared to pristine material.

Promoting behavior of yttrium over nickel supported on alumina-yttria catalysts in the ethanol steam reforming reaction

The effect of different amounts of Y2O3 (5%wt, 10%wt and 15%wt) on the characteristics of nickel supported over mixed non-crystalline Al2O3Y2O3 was investigated. These materials were tested in ethanol steam reforming reaction. Prior to reaction, the materials were characterized by N2 adsorption, X-ray diffraction, temperature programmed reduction, temperature programmed desorption of ammonia (NH3-TPD), and Nuclear Magnetic Resonance. As the yttrium content in the catalytic support increased, nickel started to reduce at lower temperatures and for high yttrium loading (10%wt and 15%wt) an increase in hydrogen uptake was observed. NH3-TPD showed that yttrium presence decreased the total acidity of alumina and also lowered the strength of the acid sites. The influences of the water to ethanol molar ratio and of the weight gas hourly space velocity on the reaction were also investigated. Yttrium containing systems decrease the presence of C2 compounds in the exhaust gases and show less formation of CO. After activity test, yttrium containing catalysts seem to present less carbon deposits than the nickel supported on pure alumina catalyst.

Versatile preparation of graphene-based nanocomposites and their hydrogen adsorption

We report the facile and versatile preparation of graphene-based nanocomposites of magnetite, silver, titania, nickel, and silicon by solid state mechanical mixing. The composites were directly employed for nitrogen and hydrogen gas adsorption studies at 77 K and equilibrium pressure of 1 atm. Under the experimental conditions the chemically synthesised graphene support had a solid state BET surface area of 499 m2/g and a total reversible hydrogen uptake of 0.5 wt.%. Among our prepared nanocomposite samples, the silver nanoparticles promoted the most significant increase in hydrogen uptake per metre squared of material by 30% when compared to the parent graphene sample. However, the total hydrogen uptake by weight percentage in the studied graphenic materials remains low. The hydrogen storage capacity observed for the graphene nanocomposites can be qualitatively accounted for by considering the contributions of the catalyst particles on the hydrogen storage, the contact between catalyst and graphene, and the structural nature of the graphene surface.

Metal–Inorganic–Organic Matrices as Efficient Sorbents for Hydrogen Storage

Stabilization of metal nanoparticles (MNPs) without re-aggregation is a major challenge. An unprecedented strategy is developed for achieving high dispersion of copper(0) or palladium(0) on montmorillonite-supported diethanolamine or thioglycerol. This results in novel metal-inorganic-organic matrices (MIOM) that readily capture hydrogen at ambient conditions, with easy release under air stream. Hydrogen retention appears to involve mainly physical interactions, slightly stronger on thioglycerol-based MIOM (S-MIOM). Thermal enhancement of desorption suggests also a contribution of chemical interactions. The increase of hydrogen uptake with prolonged contact times arises from diffusion hindrance, which appears to be beneficial by favoring hydrogen entrapment. Even with compact structures, MIOMs act as efficient sorbents with much higher efficiency factor (1.14-1.17 mmol H 2 m(-2)) than many other sophisticated adsorbents reported in the literature. This opens new prospects for hydrogen storage and potential applications in microfluidic hydrogenation reactions.

Evaluation of the physi- and chemisorption of hydrogen in alkali (Na, Li) doped fullerenes

In this study, alkali doped fullerenes synthesized by two different solvent assisted mixing techniques are compared for their hydrogen uptake activity. In particular, we investigated the interaction of hydrogen with lithium and sodium doped fullerenes via physisorption. In addition, we present the first mass spectrometric evidence for the formation of C60H60 via chemisorption. Hydrogen physisorption isotherms up to 1 atm at temperatures ranging from 77 K to 303 K were measured demonstrating an increase in hydrogen uptake versus pure C60 and increased isosteric heats of adsorption for the lithium doped fullerene Li12C60. The hydrogen uptake in Na6C60, Li6C60, and Li12C60 was enhanced compared to pure C60. However, despite these improvements the low amount of physisorbed hydrogen at 1 atm and 77 K in these materials suggests that fullerenes do not possess enough accessible surface area to effectively store hydrogen due to their close packed crystalline nature.

Magnetic susceptibility of the Pd–Co–H system

Abstract In this study, the magnetic susceptibility of the Pd–Co–H system was simultaneously measured with pressure–composition isotherms at ambient temperature. The magnetic susceptibility of the system abruptly decreased as the hydrogen content increased to 0.02 for all Pd–Co alloys under study. In the plateau region, the susceptibility decreased linearly with an increase in hydrogen uptake. The single metal hydride phase exhibited weak magnetic susceptibility. These behaviours were qualitatively interpreted in terms of the electronic structure of the Pd–Co–H system. The unoccupied down-spin band of Co just above the Fermi level gradually decreased with increasing hydrogen uptake; thus, the magnetic moment arising from uncompensated spin reduced, and the ferromagnetic transition temperature decreased.

Preparation and hydrogen storage capacity of templated and activated carbons nanocast from commercially available zeolitic imidazolate framework

A commercially available zeolitic imidazolate framework (ZIF), namely Basolite Z1200 (BASF), has been used as template for nanocasting of highly microporous ZIF-templated carbon. The “hard template carbonization technique” consists of liquid impregnation of furfuryl alcohol into the pores of the ZIF followed by polymerization and then carbonization during which the ZIF template is removed to generate the microporous carbon (90–95% microporosity) with a surface area of 900–1100 m2 g−1 and a pore volume of ca. 0.7 cm3 g−1. Chemical activation (with KOH at a relatively low temperature of 700 °C for 1 h and a carbon/KOH weight ratio of 1 : 4) of the ZIF-templated carbons increases their porosity by between 30 and 240% depending on their carbonization temperature, to achieve a surface area of up to 3200 m2 g−1 and a pore volume of 1.94 cm3 g−1. Despite the drastic increase in porosity, the activated ZIF-templated carbons retain significant microporosity with micropores contributing 80–90% of surface area and 60–70% of pore volume. This occurs because the activation process mainly enhances existing porosity rather than creating new larger pores. The activation enhances the hydrogen uptake capacity of the ZIF-templated carbons by between 25 and 140% from 2.6–3.1 wt% to the range 3.9–6.2 wt% (at −196 °C and 20 bar). The increase in hydrogen uptake after activation is closely related to rises in the micropore surface area and micropore volume rather than overall increase in porosity. Due to their microporous nature, the carbons exhibit high hydrogen storage density in the range 13.0–15.5 μmol H2 m−2, which is much higher than that of most high surface area activated carbons.

Effect of Re on product yields and deactivation patterns of naphtha reforming catalyst

The effect of rhenium concentration on the activity and stability of Pt–Re/Al 2O 3 catalysts used in naphtha reforming were studied by varying the rhenium concentration. The samples were prepared by the co-impregnation method on chloride alumina. The platinum content was 0.3 wt.%, and the rhenium loading was varied to obtain Re/Pt weight ratios of 1.0, 1.5, 2.0, 2.5 and 3. Re loading greatly influenced the catalytic properties and product yields in naphtha reforming. TPR profiles indicated the increase in hydrogen uptake, but decrease in reducibility of rhenium with increase of rhenium loading. At low rhenium loadings, the catalyst exhibited the presence of two groups of rhenium reduced at two different temperatures, while the peaks are merged in to a single sharp peak at higher rhenium loadings. Increase in aromatic yields and decrease in cracking yields was observed up to 0.6 wt.% rhenium loading (Re/Pt weight ratio = 2.0). Further increase of Re caused decrease in xylene and C 9+ with simultaneous increase of benzene, toluene, methane and ethane yields. The catalyst with 0.6 wt.% rhenium exhibited best aromatic yields and highest hours-on-oil performance.

Nickel affects activity more than expression of hydrogenase protein in Frankia.

The effects of nickel on hydrogen uptake and the post-translational processing of the large subunit of the hydrogenase protein in three Frankia strains (one isolated from an Alnus-Frankia symbiosis and two from Casuarina-Frankia associations) were investigated. All three strains responded to the addition of nickel with an increase in hydrogen uptake. Additional nickel did not affect nitrogenase activity, however evolved hydrogen was detected in Frankia KB5 in the absence of additional nickel, indicating that hydrogenase was not active. No increase in the processing rate of the hydrogenase large subunit was found with increasing nickel concentrations for any of the strains, indicating that the strategy for regulating hydrogenase in Frankia is different from that in other microorganisms.

Effect of annealing treatment on electrochemical properties of Mm-based hydrogen storage alloys for Ni/MH batteries

Several multi-component Mm-based hydrogen storage alloys with cobalt content from 0.8–1.0 have been prepared. The hydrogen absorption–desorption characteristics in gas–solid reactions and the electrochemical properties as MH electrodes have been investigated. The addition of small amounts of Al effectively lowers the hydrogen equilibrium pressure and improves the cycling stability of the alloys. Electrochemical measurements show that the MmNi 3.4Co 1.0Mn 0.5Al 0.1 alloy exhibits a maximum electrochemical capacity of ∼322 mA h g −1 with a capacity decay of about 19.5% after 100 cycles. Annealing treatments flatten the plateau region and lower the hydrogen equilibrium pressure, which results in an increase of hydrogen uptake below 1 atm. The increasing trend of hydrogen storage capacity from the as-cast sample to the annealed sample in the gas–solid reactions is in good agreement with the electrochemical results. The electrochemical discharge capacity of the MmNi 3.4Co 1.0Mn 0.5Al 0.1 alloy increases to 334 mA h g −1 and 340 mA h g −1 after annealing for 3 h and 28 h, respectively, from 322 mA h g −1 in the as-cast condition. The electrochemical cycling stability of the annealed samples was also greatly improved. The capacity decay for both annealed samples is about 8.3% and 6.8%, respectively, after 100 charge–discharge cycles. It was suggested that annealing treatments enhance the compositional homogeneity and cause the secondary phase (separated phase) to dissolve in main phase, which result in the improvement of electrochemical cycling stability of the alloy electrodes.

The role of nitrogen and oxygen surface groups in the behavior of carbon-supported iron and ruthenium catalysts

A carbon prepared from a copolymer Saran, and the products resulting from its reaction with NH 3 and HNO 3 under different experimental conditions to introduce nitrogen and oxygen surface groups, have been used as supports for Fe and Ru catalysts. The catalysts have been characterized by H 2 and CO chemisorption, X-ray line broadening and transmission electron microscopy were used to estimate metal particle sizes. There is, for Fe catalysts, an increase in hydrogen uptake and a decrease in CO uptake with increasing nitrogen content of the support and a decrease of both uptakes with increasing oxygen content. There is, however, in the case of Ru, an increase in both H 2 and CO uptake with increasing nitrogen content of the support. The results obtained in the hydrogenation of CO at 523 K and 101 KPa do not, in all cases, follow the sequence observed in the chemisorption experiments; it seems as if the functional groups introduced on the carbon are not sufficient to produce sensible changes in activity or selectivity of the catalysts in this reaction. Some effect is observed only in highly dispersed Fe catalysts supported on carbons treated with ammonia. Moreover, the hydrogenolysis of n-butane at 573 K (Fe catalysts) or 413 K (Ru catalysts) seems to be clearly affected by the nitrogen content of the support, especially in catalysts prepared from Fe(CO) 5.