Influence of fillers on hydrogen penetration properties and blister fracture of rubber composites for O-ring exposed to high-pressure hydrogen gas

Ethylene–propylene rubber (EPDM) and nitrile–butadiene rubber (NBR) composites having carbon black, silica, and no fillers were exposed to hydrogen gas at a maximum pressure of 10 MPa; then, blister tests and the measurement of hydrogen content were conducted. The hydrogen contents of the composites were proportional to the hydrogen pressure, i.e., the behavior of their hydrogen contents follows Henry's law. This implies that hydrogen penetrates into the composite as a hydrogen molecule. The addition of carbon black raised the hydrogen content of the composite, while the addition of silica did not. Based on observations, the blister damages of composites with silica were less pronounced, irrespective of the hydrogen pressures. This may be attributed to their lower hydrogen content and relatively better tensile properties than the others.     

Spillover enhanced hydrogen uptake of Pt/Pd doped corncob-derived activated carbon with ultra-high surface area at high pressure

Corncob-derived activated carbon (CAC) was prepared by potassium hydroxide activation. The Pt/Pd-doped CAC samples were prepared by two-step reduction method (ethylene glycol reduction plus hydrogen reduction). The as-obtained samples were characterized by N₂-sorption, TEM and XRD. The results show the texture of CAC is varied after doping Pt/Pd. The Pd particles are easier to grow up than Pt particles on the surface of activated carbon. For containing Pt samples, the pore size distributions are different from original sample and Pd loaded sample. The hydrogen uptake results show excess hydrogen uptake capacity on the Pt/Pd-doped CAC samples are higher than pure CAC at 298 K, which should be attributed to hydrogen spillover effects. The 2.5%Pt and 2.5%Pd hybrid doped CAC sample shows the highest hydrogen uptake capacity (1.65 wt%) at 298 K and 180 bar, The particle size and distribution of Pt/Pd catalysts could play a crucial role on hydrogen uptake by spillover. The total hydrogen storage capacity analysis show that total H₂ storage capacities for all samples are similar, and spillover enhanced H₂ uptakes of metal-doped samples could not well support total H₂ storage capacity. The total pore volume of porous materials also is a key factor to affect total hydrogen storage capacity.     

Mg-based composites for enhanced hydrogen storage performance

Hydrogen storage in solids of hydrides is advantageous in comparison to gaseous or liquid storage. Magnesium based materials are being studies for solid-state hydrogen storage due to their advantages of high volumetric and gravimetric hydrogen storage capacity. However, unfavorable thermodynamic and kinetic barriers hinder its practical application. In this work, we presented that kinetics of Mg-based composites were significantly improved during high energy ball milling in presence of various types of carbon, including plasma carbon produced by plasma-reforming of hydrocarbons, activated carbon, and carbon nanotubes. The improvement of the kinetics and de-/re-hydrogenation performance of MgH₂ and TiC-catalysed MgH₂ by introduction of carbon are strongly dependent on the milling time, amount of carbon and carbon structure. The lowest dehydrogenation temperature was observed at 180 °C by the plasma carbon–modified MgH₂/TiC. We found that nanoconfinement of carbon structures stabilised Mg-based nanocomposites and hinders the nanoparticles growth and agglomeration. Plasma carbon was found to show better effects than the other two carbon structures because the plasma carbon contained both few layer graphene sheets that served as an active dispersion matrix and amorphous activated carbons that promoted the spill-over effect of TiC catalysed MgH₂. The strategy in enhancing the kinetics and thermodynamics of Mg-based composites is leading to a better design of metal hydride composites for hydrogen storage.     

High pressure hydrogen adsorption apparatus: Design and error analysis

In the present work, design and operation of a high pressure gas adsorption apparatus at room temperature and at pressures up to 100 bar are discussed. A theoretical and experimental error analysis is done to determine accuracy and robustness of the measurements. For this study, activated carbon was selected as the adsorbent and hydrogen as the adsorbate gas. A sensitivity analysis was done by taking into account the effects of temperature, pressure, volume and weight of the sample. The analysis shows that the volumes of the sample and reference cells as determined by helium-free space measurements have significant effect on the accuracy of the adsorption uptake measurement. For instance, a 0.1% error in the measurement of either volume led to approximately a 3% error in hydrogen uptake measurement at 298 K and 100 bar.     

Formation of BCC TiFe hydride under high hydrogen pressure

We investigated the hydrogenation of a binary TiFe alloy at 5 GPa and 600 °C by in situ synchrotron radiation X-ray diffraction measurements. After formation of a solid solution of hydrogen in TiFe, an order–disorder phase transition in the metal lattice of TiFe occurred, which yielded a BCC TiFe hydride. The unit cell volume of the BCC hydride increased by 21.0% after the hydrogenation reaction. The volume expansion was larger than that of a γ-hydride TiFeH_1.9 prepared by hydrogenation near ambient conditions.     

Hydrogen induced microstructure evolution of titanium matrix composites

The effect of melt hydrogenation on microstructure evolution of Ti-6Al-4V matrix composites was investigated in this study. Molten alloy was hydrogenated with a mixture of hydrogen and argon, and reinforced at 5% total volume fraction with a 1:1 mol ratio mixture of TiB and TiC particles. Microstructure of as cast composites showed hydrogen induced more TiB whiskers with higher length-diameter ratio (LDR), because hydrogen accelerated atomic diffusion and then increased growth rate of TiB whiskers. Hot compression results indicated hydrogen reduced peak flowing stress. Microstructure of as compressed composites indicated hydrogen encouraged decomposition of residual lamellas. Hydrogen eliminated most cracks and holes along the interface between ceramic particles and matrix. Compared with unhydrogenated composites, the original ceramic particles in hydrogenated composites were fragmented into smaller pieces after compression. Electron back-scattered diffraction and transmission electron microscopy results indicated hydrogen increased volume fraction of dynamic recrystallization (DRX). And hydrogen decreased the density of dislocations nearby the interface.     

A synthesis method for cobalt doped carbon aerogels with high surface area and their hydrogen storage properties

Carbon aerogels doped with nanoscaled Co particles were prepared by first coating activated carbon aerogels using a wet-thin layer coating process. The resulting metal-doped carbon aerogels had a higher surface area (∼1667 m² g⁻¹) and larger micropore volume (∼0.6 cm³ g⁻¹) than metal-doped carbon aerogels synthesised using other methods suggesting their usefulness in catalytic applications. The hydrogen adsorption behaviour of cobalt doped carbon aerogel was evaluated, displaying a high ∼4.38 wt.% H₂ uptake under 4.6 MPa at −196 °C. The hydrogen uptake capacity with respect to unit surface area was greater than for pure carbon aerogel and resulted in ∼1.3 H₂ (wt. %) per 500 m² g⁻¹. However, the total hydrogen uptake was slightly reduced as compared to pure carbon aerogel due to a small reduction in surface area associated with cobalt doping. The improved adsorption per unit surface area suggests that there is a stronger interaction between the hydrogen molecules and the cobalt doped carbon aerogel than for pure carbon aerogel.     

Thermo-catalytic decomposition of propane over carbon black in a fluidized bed for hydrogen production

Thermo-catalytic decomposition of propane to solid carbon and hydrogen was examined for hydrogen production without CO₂ emission. The reaction was carried out over a carbon black catalyst in a bench-scale fluidized bed reactor. Effects of reaction temperature on the propane conversion and product distribution were examined. Catalytic activity of the carbon black was maintained stable for longer than 8 h in spite of carbon deposition. From 600 to 650 °C, the propane conversion increased sharply with propylene produced in a considerably larger amount than methane. As the reaction temperature further increased up to 800 °C, the major hydrocarbon product was methane; the production of propylene decreased rapidly and ethylene was the next most abundant product. The surface area of the carbon black was decreased as the reaction proceeded due to carbon deposition. Surface morphology of the used carbon black was observed by TEM and the change of the aggregates size was measured.     

A study on optimal pore range for high pressure hydrogen storage behaviors by porous hard carbon materials prepared from a polymeric precursor

In this study, activated polymer-based hard carbons were prepared using various steam activation conditions in order to enhance their hydrogen storage ability. The structural characteristics of the activated carbons were observed by X-ray diffraction and Raman spectroscopy. The N₂ adsorption isotherm characteristics at 77 K were confirmed by Brunauer-Emmett-Teller, Barrett-Joyner-Halenda and non-local density functional theory equations. The hydrogen storage behaviours of the activated carbons at 298 K and 10 MPa were studied using a Pressure-Composition-Temperature apparatus. From the results, specific surface areas and total pore volume of the activated carbons were determined to be 1680–2320 m²/g and 0.78–1.39 cm³/g, respectively. It was also observed that various pore size distributions were found to be dependent on the functions of activation time. In the observed result, the hydrogen adsorption of APHS-9-4 increased about 30% more than that of as-prepared hard carbon. This indicates that hydrogen storage capacity could be a function not only of specific surface area or total pore volume, but also of micropore volume fraction in the range of 0.63–0.78 nm of adsorbents.     

Optimizing parameters affecting synthetize of CuBTC using response surface methodology and development of AC@CuBTC composite for enhanced hydrogen uptake

CuBTC, a widely studied metal-organic framework, is a promising candidate for industrial applications owing to its easy synthesis procedure and excellent textural properties. In this research CuBTC was synthesized by solvothermal method with the purpose of hydrogen uptake. Response surface methodology (RSM) was employed in order to determine the optimum synthesis condition with the highest hydrogen capacity. Amount of ligand, volume of solvent, synthesis temperature, and synthesis time were chosen as independent variables, while the amount of hydrogen uptake was selected as the response. Subsequently, activated carbon (AC) was incorporated within the optimized CuBTC structure as a “void space filling agent” and adsorption behavior of AC@MOF composite was evaluated from the view point of different AC contents. It was observed that the hydrogen uptake of AC@CuBTC composite was increased compared to bare CuBTC samples. This finding could be attributed to effective utilization of micropore volume of CuBTC structure by AC incorporation.     

An energy-efficient plasma methane pyrolysis process for high yields of carbon black and hydrogen

A novel thermal plasma process was developed, which enables economically viable commercial-scale hydrogen and carbon black production. Key aspects of this process are detailed in this work. Selectivity and yield of both solid, high-value carbon and gaseous hydrogen are given particular attention. For the first time, technical viability is demonstrated through lab scale reactor data which indicate methane feedstock conversions of >99%, hydrogen selectivity of >95%, solid recovery of >90%, and the ability to produce carbon particles of varying crystallinity having the potential to replace traditional furnace carbon black. The energy intensity of this process was established based on real-time operation data from the first commercial plant utilizing this process. In its current stage, this technology uses around 25 kWh per kg of H2 produced, much less than water electrolysis which requires approximately 60 kWh per kg of H2 produced. This energy intensity is expected to be reduced to 18–20 kWh per kg of hydrogen with improved heat recovery and energy optimization.     

Improvement of the LiBH4 hydrogen desorption by inclusion into mesoporous carbons

LiBH₄ hydrogen desorption is strongly improved by its confinement to the nanoscale into a mesoporous carbon, prepared by the template method, having a pore diameter near 4 nm and a porous volume of 1.1 cm³ g⁻¹. The LiBH₄/carbon composites are prepared by room temperature impregnations of the carbon matrix with LiBH₄ solubilized within ethers. LiBH₄/carbon composites with a 33:67 weight ratio show excellent desorption kinetics with a hydrogen release of 3.4 wt.% in 90 min at 300 °C, whereas the decomposition of neat LiBH₄ is not significant at the same temperature. Moreover, both Differential Scanning Calorimetry and Thermal Desorption Spectroscopy experiments show that the hydrogen release for the 33:67 LiBH₄/carbon composite occurs in one single step immediately above the LiBH₄ melting temperature (280 °C) without any formation of intermediate compounds (like dodecaborane) as encountered with neat LiBH₄. Such modification of the hydrogen release mechanism path was never reported for confined LiBH₄ nanoparticles. Last the presence of the carbonaceous matrix is expected to be largely beneficial for handling the heat transfer associated with the endothermic character of the LiBH₄ decomposition process.     

Dehydrogenation and low-pressure hydrogenation properties of NaAlH4 confined in mesoporous carbon black for hydrogen storage

For hydrogen to be successfully used as an energy carrier in a new renewable energy driven economy, more efficient hydrogen storage technologies have to be found. Solid-state hydrogen storage in complex metal hydrides, such as sodium alanate (NaAlH₄), is a well-researched candidate for this application. A series of NaAlH₄/mesoporous carbon black composites, with high NaAlH₄ content (50–90 wt%), prepared via ball milling have demonstrated significantly lower dehydrogenation temperatures with intense dehydrogenation starting at ∼373 K compared to bulk alanate's ≥ 456 K. Dehydrogenation/hydrogenation cycling experiments have demonstrated partial hydrogenation at 6 MPa H₂ and 423 K. The cycling experiments combined with temperature-programmed dehydrogenation and powder X-ray diffraction have given insight into the fundamental processes driving the H₂ release and uptake in the NaAlH₄/carbon composites. It is established that most of the hydrogenation behavior can be attributed to the Na₃AlH₆ ↔ NaH transition.     

Synthesis and characterization of Pt‐CMK‐3 hybrid nanocomposite for hydrogen storage

The nanometric carbon CMK‐3 modified with Pt was synthesized and applied as a reservoir for hydrogen uptake. We found that the newly synthesized hybrid composites exhibited significantly enhanced H₂ storage. The approach that we have followed includes synthesis of nanostructures with the experimental study of its adsorption capacity and storage properties. In summary, we have shown that CMK‐3 ordered porous carbon modified with Pt nanoclusters is a promising material for hydrogen uptake. The samples were characterized by X‐ray diffraction, N₂ isotherms, X‐ray photoelectron spectra and transmission electron microscopy. The nanoparticles of Pt (~1.7 nm) incorporated onto the nanostructured carbon CMK‐3 showed higher hydrogen uptake at low and high pressures (3.3 wt% of H₂ sorption at 10 bar and 77 K) than CMK‐3. Copyright © 2014 John Wiley & Sons, Ltd.     

NiGa modified carbon-felt cathode for hydrogen production

In this study, known electrocatalytic active metal nickel and low amount of gallium were electrodeposited on carbon felt electrode for hydrogen evolution reaction in alkali medium. Morphological and structural analyses of prepared electrodes were determined by scanning electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic activity of obtained electrodes for hydrogen evolution reaction was determined with cathodic polarization curves, electrochemical impedance spectroscopy, discharge potential measurements, hydrogen volume measurements at constant potential and durability tests. It was found that the electrodeposition of low amount of gallium over the nickel coated carbon felt electrode increases the hydrogen evolution reaction activity and decreases the overpotential for hydrogen region. The electrocatalytic activity of nickel and gallium deposited on carbon felt electrode was explained with active sites of surface and synergistic effect of nickel and gallium created by high surface area of carbon felt.     

Hydrogen storage of nanostructured TiO2-impregnated carbon nanotubes

Hydrogen uptake study of carbon nanotubes (CNTs) impregnated with TiO₂-nanorods and nanotubes has been performed at room temperature and moderate hydrogen pressures of 8–18 atm. Under hydrothermal synthesis conditions, nanorods (NRs) and nanoparticles (NPs) are found to form either of the two polymorphic phases, i.e., nanorods are formed of predominantly anatase phase while nanoparticles are formed of rutile phase. NRs and NPs are introduced into the CNT matrix via the wetness-impregnation method. These composites store up to 0.40 wt.% of hydrogen at 298 K and 18 atm, which is nearly five times higher the hydrogen uptake of pristine CNTs. The excess amount of hydrogen stored in TiO₂-impregnated CNTs is determined from the amount of TiO₂ in the sample and the measured hydrogen uptake of TiO₂ nanoparticles. Higher hydrogen uptake of NP-impregnated CNTs when compared pristine CNTs is accounted for by considering initial binding of hydrogen on TiO₂ and subsequent spillover in CNT–TiO₂-NPs.     

Study of hydrogen physisorption on nanoporous carbon materials of different origin

Hydrogen adsorption capabilities of different nanoporous carbon, i.e. amorphous carbons obtained by chemical activation (with KOH) of a sucrose-derived char previously ground by ball milling and carbon replicas of NH₄-Y and mesocellular silica foam (MSU-F) inorganic templates, were measured and correlated to their porous properties. The porous texture of the prepared carbon materials was studied by means of N₂ and CO₂ adsorption isotherms measured at −196 °C and 0 °C, respectively. Comparison with nanoporous carbons obtained without pre-grinding the sucrose-derived char [12] shows that the ball milling procedure favours the formation of highly microporous carbon materials even at low KOH loadings, having a beneficial effect of the interaction between the char particles and the activating agent. Hydrogen adsorption isotherms at −196 °C were measured in the 0.0-1.1 MPa pressure range, and a maximum hydrogen adsorption capacity of 3.4 wt.% was obtained for the amorphous carbon prepared by activation at 900 °C with a KOH/char weight ratio of 2. Finally, a linear dependence was found between the maximum hydrogen uptake at 1.1 MPa and the samples microporous volume, confirming previous results obtained at −196 °C and sub-atmospheric pressure [12].     

A critical review on improving hydrogen storage properties of metal hydride via nanostructuring and integrating carbonaceous materials

Hydrogen-based economy has a great potential for addressing the world's environmental concerns by using hydrogen as its future energy carrier. Hydrogen can be stored in gaseous, liquid and solid-state form, but among all solid-state hydrogen storage materials (metal hydrides) have the highest energy density. However, hydrogen accessibility is a challenging step in metal hydride-based materials. To improve the hydrogen storage kinetics, effects of functionalized catalysts/dopants on metal atoms have been extensively studied. The nanostructuring of metal hydrides is a new focus and has enhanced hydrogen storage properties by allowing higher surface area and thus reversibility, hydrogen storage density, faster and tunable kinetics, lower absorption and desorption temperatures, and durability. The effect of incorporating nanoparticles of carbon-based materials (graphene, C60, carbon nanotubes (CNTs), carbon black, and carbon aerogel) showed improved hydrogen storage characteristics of metal hydrides. In this critical review, the effects of various carbon-based materials, catalysts, and dopants are summarized in terms of hydrogen-storage capacity and kinetics. This review also highlights the effects of carbon nanomaterials on metal hydrides along with advanced synthesis routes, and analysis techniques to explore the effects of encapsulated metal hydrides and carbon particles. In addition, effects of carbon composites in polymeric composites for improved hydrogen storage properties in solid-state forms, and new characterization techniques are also discussed. As is known, the nanomaterials have extremely higher surface area (100–1000 time more surface area in m²/g) when compared to the bulk scale materials; thus, hydrogen absorption and desorption can be tuned in nanoscale structures for various industrial applications. The nanoscale tailoring of metal hydrides with carbon materials is a promising strategy for the next generation of solid-state hydrogen storage systems for different industries.     

Effect of initial pressure on laminar combustion characteristics of hydrogen enriched natural gas

Flame propagation of premixed natural gas–hydrogen–air mixtures was studied in a constant volume combustion bomb. Laminar burning velocities and mass burning fluxes were obtained under various hydrogen fractions and equivalence ratios with various initial pressures, while flame stability and their influencing factors (Markstein length, density ratio and flame thickness) were obtained by analyzing the flame images at various hydrogen fractions, initial pressures and equivalence ratios. The results show that hydrogen fraction, initial pressure as well as equivalence ratio have combined influence on both unstretched laminar burning velocity and flame instability. Meanwhile, according to flame propagation pictures taken by the high speed camera, flame stability decreases with the increase of initial pressures; for given equivalence ratio and hydrogen fraction, flame thickness is more sensitive to the variation of the initial pressure than to that of the density ratio.     

Numerical simulation of stress distribution for CF/EP composites in high temperatures

The high-performance carbon fiber materials can be obtained by decomposing carbon fiber reinforced resin matrix composites using thermally activated oxide semiconductors. This paper established the representative volume element (RVE) of carbon fiber/epoxy resin composites, and investigated the structure destruction of composites in the recycling process based on analysis of the stress and strain distribution by the thermomechanical coupling module of Digimat. The results indicated that the maximum thermal stress of the epoxy resin appeared in the poor resin region, while the minimum appeared in the resin-rich region; the stress of the carbon fibers in poor resin region was greater than that in the resin-rich region; the maximum stress of composites appeared in the interface layers when the temperature ranged from 350 to 500?°C, and the maximum thermal stress was 196.9–281.3?MPa, as well as the maximum shear stress was 98.2–140.3?MPa; the maximum peeling stress perpendicular to the fiber directions was 53.7–157.3?MPa; the strain of the interface layers and carbon fibers were the smaller than that of the resin matrix, whose maximum strain ranged from 0.0622 to 0.0889. The structure destruction of the composites was caused by both the peeling stress and the interfacial shear stress in recycling.