Hydrogen Adsorption Capacity Research Articles

Nanoarchitectures Based on Layered Titanosilicates Supported on Glass Fibers: Application to Hydrogen Storage

This work reports on the synthesis of nanosheets of layered titanosilicate JDF-L1 supported on commercial E-type glass fibers with the aim of developing novel nanoarchitectures useful as robust and easy to handle hydrogen adsorbents. The preparation of those materials is carried out by hydrothermal reaction from the corresponding gel precursor in the presence of the glass support. Because of the basic character of the synthesis media, silica from the silicate-based glass fibers can be involved in the reaction, cementing its associated titanosilicate and giving rise to strong linkages on the support with the result of very stable heterostructures. The nanoarchitectures built up by this approach promote the growth and disposition of the titanosilicate nanosheets as a house-of-cards radially distributed around the fiber axis. Such an open arrangement represents suitable geometry for potential uses in adsorption and catalytic applications where the active surface has to be available. The content of the titanosilicate crystalline phase in the system represents about 12 wt %, and this percentage of the adsorbent fraction can achieve, at 298 K and 20 MPa, 0.14 wt % hydrogen adsorption with respect to the total mass of the system. Following postsynthesis treatments, small amounts of Pd (<0.1 wt %) have been incorporated into the resulting nanoarchitectures in order to improve their hydrogen adsorption capacity. In this way, Pd-layered titanosilicate supported on glass fibers has been tested as a hydrogen adsorbent at diverse pressures and temperatures, giving rise to values around 0.46 wt % at 298 K and 20 MPa. A mechanism of hydrogen spillover involving the titanosilicate framework and the Pd nanoparticules has been proposed to explain the high increase in the hydrogen uptake capacity after the incorporation of Pd into the nanoarchitecture.

The hydrogen storage capacity of mono-substituted MOF-5 derivatives: An experimental and computational approach

Herein we report the synthesis and hydrogen storage capability of four simple MOF-5 modifications, i.e. CH3-MOF-5, OCH3-MOF-5, Br-MOF-5 and Cl-MOF-5. The mono-substituted MOF-5s, with the exception of OCH3-MOF-5, exhibit the same topology as that of unsubstituted MOF-5. The BET surface areas are in the range of 680–2750m2g−1 for this series. Introducing these functional groups appears to have a significant effect on the thermal stability of the resulting frameworks. The thermal stability of CH3-MOF-5 is comparable to that of MOF-5 after heat-treatment, i.e. vacuum dried at 200°C for 40h, whereas the structure of Cl-MOF-5 collapses under the same conditions. Activated MOF-5, CH3-MOF-5, Br-MOF-5 and Cl-MOF-5 show 1.44wt.%, 1.47wt.%, 1.08wt.% and 0.99wt.% of hydrogen uptake capacities at 77K and 1bar, respectively. Experimental and computational results reveal that the introduction of –CH3, –Br and –Cl has only a minor effect on the isosteric heat of hydrogen adsorption for MOF-5 and the experimental values are in the range of 2.8 – 3.0kJmol−1 for all derivatives. This explains the similar hydrogen adsorption capacities of MOF-5 and CH3-MOF-5. The poor porous structures of Br-MOF-5 and Cl-MOF-5, however, result in lower hydrogen adsorption capacities compared to MOF-5 despite their similar isosteric heat of hydrogen adsorption. At high pressures (>20bar), the excess hydrogen capacity appears to be a strong function of the specific surface area.

Hydrogen adsorption capacity of adatoms on double carbon vacancies of graphene: A trend study from first principles

Structural stability and hydrogen adsorption capacity are two key quantities in evaluating the potential of metal-adatom decorated graphene for hydrogen storage and related devices. We have carried out extensive density functional theory calculations for the adsorption of hydrogen molecules on 12 different adatom (Ag, Au, Ca, Li, Mg, Pd, Pt, Sc, Sr, Ti, Y, and Zr) decorated graphene surfaces where the adatoms are found to be stabilized on double carbon vacancies, thus overcoming the ``clustering problem'' that occurs for adatoms on pristine graphene. Ca and Sr are predicted to bind the greatest number, namely six, of H${}_{2}$ molecules. We find an interesting correlation between the hydrogen capacity and the change of charge distribution with increasing H${}_{2}$ adsorption, where Ca, Li, Mg, Sc, Ti, Y, Sr, and Zr adatoms are partial electron donors and Ag, Au, Pd, and Pt are partial electron acceptors. The ``18-electron rule'' for predicting maximum hydrogen capacity is found not to be a reliable indicator for these systems.

Synthesis of Carbon-Based Nano Materials for Hydrogen Storage

The aim of this study was to synthesize the carbon-based nanomaterials and determine their hydrogen storage capacities. Carbon nanotubes (CNTs) were first synthesized by chemical vapor deposition (CVD) of acetylene (C2H2) on a magnesium oxide (MgO) powder impregnated with an iron nitrate (Fe(NO3)3·9H2O) solution. The synthesis parameters were selected as the synthesis temperatures of 500 and 800°C, the iron content in the precursor of 5% and the synthesis time of 30 minutes. The synthesized material was purified by using HCl at 75°C for 15 hours. After synthesis of CNTs, the polyaniline-doped H3BO3 and BF3 and composites were prepared by coagulation method. The synthesized CNTs and composites were characterized by transmission electron microscopy, FT-IR spectroscopy, Raman spectroscopy and thermogravimetric analyzer. The BET specific surface areas were obtained from the nitrogen adsorption isotherms at -196°C. The hydrogen storage capacities of these carbonaceous materials were measured using volumetric method. It was found that the hydrogen adsorption capacities were changed in the range between 0.44 and 3.67wt% at the liquid nitrogen temperature and gas pressure up to 100 bar.

Novel BN porous-hollow nanorods: synthesis, tunable dimensions, property and formation mechanism

In this paper, we used a high pressure benzene-thermal method to successfully prepare novel BN porous-hollow nanorods. Herein, thiophene is introduced as a catalyst to eliminate the benzene carbonization at high temperature. The alveolate porous wall of the nanorods is stacked up by small nanoflakes aligned vertically in the axial direction. In the high pressure solvothermal system, the diameter and wall thickness of the nanorods can be simply adjusted by the content of thiophene, temperature and pressure. A possible “gas–liquid–solid” mechanism is proposed to explain the formation of 1D BN nanorods. Another novel formation mechanism of the hollow nanorods is elaborated by observing the evolution process of the porous-hollow nanostructures. The method may provide a new idea to be used in preparing other porous-hollow nanostructures. In addition, the hierarchical porous-hollow nanorods exhibit an excellent hydrogen uptake property of 2.6 wt% at 298 K and 90 bar. In particular, the adsorption capacity per unit specific surface area was calculated to be 2.2 × 10−2 wt% m−2 g. This is a rather high value of hydrogen adsorption capacity for BN nanomaterials.

Light metals decorated covalent triazine-based frameworks as a high capacity hydrogen storage medium

The structural stability and hydrogen adsorption capacity of an alkali (Li, Na and K) and alkali earth (Mg and Ca) metal atom decorated covalent triazine-based framework (CTF-1) are studied using ab initio density functional calculations. The calculation results revealed that Li, Na, K and Ca atoms can be adsorbed on the CTF-1 with the formation of a uniform and stable coverage due to the charge transfer between the metal atoms and the CTF-1 substrate, thus avoiding the clustering problem that occurs for the decoration of metal atoms on other substrates. The metal decorated CTF-1 could adsorb up to 30 hydrogen molecules with an average binding energy of ∼0.16–0.26 eV/H2, corresponding to a gravimetric density of 12.3, 10.3 and 8.8 wt% for the CTF–Li6, CTF–Na6 and CTF–Ca6 complexes, respectively, thereby enabling the Li, Na and Ca decorated covalent triazine-based frameworks to be very promising materials for effective reversible hydrogen storage at near ambient conditions.

Hydrogen storage of Mg-decorated closo-hexaborate B6H62-

Hydrogen storage capacity of Mg-decorated closo-hexaborate B6H62- has been studied using density functional theory. The binding strength of Mg atom is sufficiently large to ensure the stability of MgB6H62-. Each Mg atom can adsorb six H2 molecules. Moreover, the larger dipole moment combined with enhanced electrostatic field around the Mg atom originates from the charge transfer from B6H62- to Mg, accounting for the higher adsorption capacity of MgB6H62- than that of MgB6H6. Hydrogen storage capacity of MgB6H62- can be up to 11.1 wt% with an average binding energy between 0.23 eV and 0.34 eV. The electrostatic field around the Mg atom can be enhanced by controlling the charge state of the metal-organic complex, thereby significantly improving the hydrogen adsorption capacity.

Hydrogen adsorption study on mixed oxides using the density functional theory

Density functional theory (DFT) calculation has been performed successfully to explore hydrogen adsorption capacity of reduced cobalt and nickel containing mixed oxides. Hydrogen adsorption behaviors of mixed oxides have been discussed via few reactivity descriptors at the M05-2X/6-311+G (d, p) level of theory. Calculated various types of energetic, reaction enthalpies and electrophilicities of cobalt and nickel clusters which are at minimum energy on potential energy surface concerned with the hydrogen adsorption phenomena attributed that reduced nickel and cobalt mixed oxides is an effective hydrogen storage material. The dynamic adsorption method as an experimental investigation has been carried out to find the performance or adsorption trend of mixed oxides. The trends of computational and experimental results are consistent in regards to hydrogen adsorption. Thermochemistry analysis predicted the phenomena are chemisorption dominant. Reduced cobalt and nickel mixed oxides are believed to be promising hydrogen storage materials where 13wt% hydrogen capacities are obtained. Thus the density functional theory is an efficient tool to explore this hydrogen storage capacity.

Piezoresistive Silicon Microresonator for Measurements of Hydrogen Adsorption in Carbon Nanotubes

In this paper, the mass detection of hydrogen adsorption using a piezoresistive resonant silicon microresonator is presented. The working principle relies on the resonant frequency shifts of the cantilevered resonator with a sample due to hydrogen adsorption. The mass of adsorbed hydrogen in carbon nanotubes (CNTs) grown on the resonator is measured experimentally after exposing to high pressure hydrogen. The mass of CNTs on the resonator is measured from resonant frequency change after the removal. According to masses of the adsorbed hydrogen and CNTs, we obtain the adsorption capacity of hydrogen into CNTs.

N2 and H2 adsorption behavior of KOH-activated ordered mesoporous carbon

Ordered mesoporous carbon, referred to as CMK-3, was synthesized by replication from SBA-15. Activated CMK-3 with developed pore structures provided a large surface area and higher hydrogen adsorption capacities after KOH activation at 1073–1223K. To characterize the pore structure of the activated samples, N2 and H2 adsorption were measured at 77K. The hydrogen adsorption of activated CMK-3 increased to 2.26wt.% at an activation temperature of 1173K due to the formation of micropores. Thus, KOH activation was not only one of the most effective methods for developing porosity, but also raised the hydrogen storage capacity of CMK-3.

Effect of Ion-Exchange Modification on Hydrogen and Carbon Dioxide Adsorption Behaviour of RhoZMOF Material

Zeolite-like metal-organic frameworks (ZMOFs) can adsorb hydrogen and carbon dioxide because of their negatively charged structures, being able to be ion exchanged with metal cations to further increase the electrostatic field inside the framework cavities. Ion exchange of RhoZMOF with alkaline and alkaline-earth metal cations was performed up to stoichiometric levels with one single ion-exchange step. Screen effect caused by water-coordinated molecules around the exchanged cations hindered the hydrogen uptake, although slightly higher heats of hydrogen adsorption were observed for Na+, Li+, Mg2+ and Ca2+ exchanged samples. Conversely, the same exchange treatment produced a very interesting enhancement in CO2 adsorption of RhoZMOF at 303 K. Moreover, because there are no water molecules surrounding the metallic cations, RhoZMOF material was exchanged with an Li+–crown–ether complex in the nitrobenzene/acetonitrile mixture, free of water. Nitrogen and hydrogen adsorption isotherms at 77 K showed higher specific surface area and hydrogen adsorption capacity than the material with hydrated cations.

Hydrogen Adsorption in Zeolite Studied with Sievert and Thermogravimetric Methods

Natural clinoptilolite (mixture from clinoptilolite, quartz and muscovite) is activated with palladium and tested for hydrogen adsorption capability at temperatures RT - 200°C. Thermogravimetric and volumetric methods showed that zeolite activated with palladium (1.25%wt) shows markedly high hydrogen adsorption capacity - up to 3 wt%. Lower amount of adsorbed hydrogen (~1.5 wt%) was found for raw zeolite and activated with higher amount of palladium sample. Hypothesis is proposed that the heating of zeolite in argon atmosphere forms and activates the pore structure in zeolite material, where hydrogen encapsulation (trapping) is believed to occur when cooling down to room temperature. An effect of catalyst (Pd) on hydrogen sorption capability is explained by spillover phenomena were less-porous fractions of natural clinoptilolite sample (quartz and muscovite) are involved.

Adsorption Behavior of Hydrogen and Deuterium on Natural Mordenite Adsorbent at 77 K

Cryogenic adsorption is effective for the recovery of low-concentration hydrogen isotopes in bulk helium gases. In a fusion power plant, application of this process is foreseen for the recovery of tritium from the blanket sweep gas and cleanup of the helium discharge exhaust gas. The authors performed a screening test to find more suitable adsorbents for the recovery of hydrogen isotopes from the bulk helium gas at liquid nitrogen temperature. The screening test indicated that a natural mordenite adsorbent has a quite high adsorption capacity for hydrogen under a helium atmosphere. For the adsorption of deuterium, it was found that the natural mordenite adsorbent possesses a high adsorption capacity even at the lower pressure range of hydrogen and deuterium. The adsorption rates of hydrogen and deuterium were quantified by analyzing breakthrough curves obtained in experiments. Evaluated effective pore diffusivities of hydrogen isotopes in the mordenite adsorbents are considerably higher than those in MS5A adsorbents. Thus, it can be said that the natural mordenite adsorbents are suitable for adsorption of hydrogen isotopes from the viewpoint of adsorption rates, as well. The results suggest that mordenite-type adsorbents are promising for the recovery of low-concentration hydrogen isotopes from the helium bulk gas.

Influence of Ti doping level on hydrogen adsorption of mesoporous Ti-SBA-15 materials prepared by direct synthesis

The influence of different Ti doping levels on the hydrogen adsorption characteristics of Ti-SBA-15 materials prepared by direct one-step synthesis was systematically investigated. The results showed that the intensity of titanol (Ti–OH) and bridging hydroxyl (Ti–O(H)–Si) groups increased with increasing Ti doping level, whereas the hydrogen adsorption capacity gradually decreased. Nitrogen physisorption, transmission electron microscopy, and small and wide-angle X-ray diffraction analyses revealed that excessive Ti doping led to the growth of TiO2 nanoparticles on the intrawall of the mesopores, which clogged the micropores. However, at comparatively low Ti doping level, Ti substitution and/or dispersion in the silica framework was activated, the number of micropores increased, and consequently the hydrogen adsorption capacity was substantially enhanced. The results from this study suggested that the hydrogen adsorption characteristics of Ti-SBA-15 materials prepared by the direct synthesis method were affected not only by generated titanol and bridging hydroxyl groups but also by the increased number of micropores.

Effect of potassium-doping on the microstructure development in polyfurfuryl alcohol – derived activated carbon

Potassium-doped activated carbon was prepared by mixing potassium salt with polyfurfuryl alcohol precursor followed by carbonization and activation. Several experimental techniques, such as thermogravimetric analysis, gas adsorption, X-ray diffraction and Raman scattering spectroscopy were employed to understand the effects of potassium on the texture and pore structures of the activated carbon, which ultimately affects the hydrogen adsorption properties. After doping with potassium, the activated carbon exhibits higher surface area, higher micropore volume, and enhanced hydrogen adsorption capacity. Understanding of how alkali metals affect surface area and micropore development in activated carbon may help to clarify the hydrogen adsorption mechanism and improve the design of suitable carbon-based hydrogen storage materials.

Effects of Mechanical Ball Milling with Active Gases on Hydrogen Adsorption Behaviors of Graphite Flakes

This study examined the effects of the mechanical milling conditions on the hydrogen adsorption behaviors of graphite flakes under different gas streams. A ball mill technique with various gas streams during treatments was used to introduce oxygen-containing functional groups on the graphite surfaces. The structural properties of graphite were evaluated by XRD, and the surface properties and textural properties were observed SEM, FT-IR, XPS and N2/77 K adsorption isotherms. The hydrogen adsorption behavior of the graphite flakes were evaluated using a volumetric method at room temperature and 100 atm. The mechanically-milled graphite flakes under an oxygen stream showed a higher concentration of oxygen functional groups and greater hydrogen adsorption capacity than that of graphite flakes under an argon stream. This suggests that oxygen functional groups have good chemical affinity with hydrogen molecules in this system.

Synthesis of zeolite-casted microporous carbons and their hydrogen storage capacity

Zeolite-casted microporous carbons (ZMiPCs) were synthesized using the replica casting method. The ZMiPC were also treated chemically by H3PO4 (A-ZMiPC) or KOH (B-ZMiPC) impregnation, to investigate the effect of the acceptor–donor interaction on the hydrogen storage behaviors. The presence of functional groups of the modified ZMiPC surfaces was confirmed by X-ray photoelectron spectroscopy. The total acidity of the carbon surfaces was determined using the Boehm titration method. The microstructure was characterized by X-ray diffraction. The N2/77K adsorption/desorption isotherms were analyzed to characterize specific surface area, pore volume, and pore size distribution of the samples. The capacity of hydrogen adsorption was evaluated using a pressure-composition-temperature apparatus at 298K/100bar. From these results, the specific surface areas and micropore volume of ZMiPC increased more than two fold compared to the zeolite template. Meanwhile, the textural properties of A-ZMiPC and B-ZMiPC were decreased by the chemical treatments. Consequently, the largest hydrogen storage was obtained on A-ZMiPC, even though their textural properties had decreased, due to a charge induced dipole interaction between the modified carbon surface and hydrogen molecules.

Zeolite-Templated Carbon Materials for High-Pressure Hydrogen Storage

Zeolite-templated carbon (ZTC) materials were synthesized, characterized, and evaluated as potential hydrogen storage materials between 77 and 298 K up to 30 MPa. Successful synthesis of high template fidelity ZTCs was confirmed by X-ray diffraction and nitrogen adsorption at 77 K; BET surface areas up to ~3600 m(2) g(-1) were achieved. Equilibrium hydrogen adsorption capacity in ZTCs is higher than all other materials studied, including superactivated carbon MSC-30. The ZTCs showed a maximum in Gibbs surface excess uptake of 28.6 mmol g(-1) (5.5 wt %) at 77 K, with hydrogen uptake capacity at 300 K linearly proportional to BET surface area: 2.3 mmol g(-1) (0.46 wt %) uptake per 1000 m(2) g(-1) at 30 MPa. This is the same trend as for other carbonaceous materials, implying that the nature of high-pressure adsorption in ZTCs is not unique despite their narrow microporosity and significantly lower skeletal densities. Isoexcess enthalpies of adsorption are calculated between 77 and 298 K and found to be 6.5-6.6 kJ mol(-1) in the Henry's law limit.

Hydrogen adsorption by woodceramics produced from biomass

Hydrogen adsorption characteristics of woodceramics, made from radiata pine wood fiber boards carbonized at 1 473K after impregnation with phenolic resin, with and without chemical treatment in an alkaline (KOH) or an acid (H2SO4) solution were investigated The hydrogen adsorption capacity is improved by chemical treatment. The chemical treatment by KOH improves the adsorption capacity more than by H2SO4. The improvement of the capacity level, in any solution, is dependent on the type of chemical in the solution and its concentration. The maximum hydrogen capacity measured at 93K is mass fraction about w(H) = 2% for the woodceramics after chemical treatment in a volume fraction φ = 50% KOH solution, although that is about w(H) = 0.7% for one without chemical treatment. The microscopic condition of pores in the woodceramics is thought to vary after chemical treatment.

General Relationship between Hydrogen Adsorption Capacities at 77 and 298 K and Pore Characteristics of the Porous Adsorbents

The hydrogen adsorption isotherms of six metal–organic frameworks (MOFs) and three microporous carbons, measured at 77 K (up to 1 bar) and 298 K (up to 100 bar), have been systematically examined for correlations with their pore characteristics. From the obtained correlations, H2 adsorption was found to occur preferentially in ultrafine pores at both 77 K (≤1 bar) and 298 K (100 bar), irrespective of the adsorbent. This represents the first experimental evidence that ultrafine pores in MOFs improve the efficiency of H2 adsorption at 298 K and at high pressures, indicating that that the low H2 storage capacities of reported ultrahigh microporous MOFs at 298 K result from the prominence of micropores with diameters 1–2 nm, which are inadequate at 298 K and high pressures. Furthermore, these correlations suggest strong links between the H2 storage capacities at 77 and 298 K, which offer an easy method for predicting H2 adsorption capacities under unapproachable conditions. This study provides guidance in the...