Hydrogen Adsorption Behavior Research Articles

Preparation of platinum impregnated activated carbon via vacuum treatment and effect on hydrogen storage rate

Hydrogen uptake was effectively enhanced by platinum impregnated activated carbon (Pt/AC) prepared in an improved vacuum treatment process. Under high vacuum condition, the precursor of Pt could be infused into deep pores of AC. The fine Pt nanoparticles (<2nm) were well dispersed in mesopores and micropores of AC after heating reduction. The characterization results indicate the modified vacuum treatment in this research effectively decreased the size and improved the dispersion of Pt catalysts. The impregnating condition of Pt nanocrystals obviously influenced specific surface area and pore structure, and also evidently resulted in dissimilar hydrogen adsorption behavior. Depending on the measurement of high pressure thermo-gravimetric analyzer under hydrogen atmosphere, the hydrogen adsorption rate could be accurately analyzed. Notably, the exceptional result was found in this investigation. Even with much lower surface area and pore volume, tiny Pt nanoparticles uniformly distributed in pores effectively assisted in hydrogen diffusing in deeper sites of AC via spillover phenomenon, and then substantially enhanced twice higher hydrogen uptake rate as comparing to the original process without vacuum treatment. It means the size and distribution of Pt catalysts in the pores of AC should be important key factors for hydrogen spillover behavior.

A study on hydrogen adsorption behaviors of open-tip carbon nanocones

Hydrogen adsorption behaviors of single-walled open-tip (tip-truncated) carbon nanocones (CNCs) with apex angles of 19.2° at temperatures of 77 and 300 K were investigated by the molecular dynamics simulations. Four nanomaterials (including three CNCs with different dimensions and a reference CNT) were analyzed to examine the hydrogen adsorption behaviors and influences of cone sharpness on the behaviors of the CNCs. Physisorption of hydrogen molecules could be observed from the distribution pattern of the hydrogen molecules adsorbed on the nanomaterials. Because of the cone geometry effect, the open-tip CNCs could have larger storage weight percentage and less desorption of hydrogen molecules (caused by the temperature growth) on their outer surfaces, as compared with those of the reference CNT. The hydrogen molecules inside the CNCs and the reference CNT, however, were noted to have similar desorption behaviors owing to the confinement effects from the structures of the nanomaterials. In addition, the sharper CNC could have higher storage weight percentage but the cone sharpness does not have evident enhancement in the average adsorption energy of the CNC. Combination of confinement and repulsion effects existing near the tip region of the CNC would be responsible for the non-enhancement feature.

Ambient rutile VO2(R) hollow hierarchitectures with rich grain boundaries from new-state nsutite-type VO2, displaying enhanced hydrogen adsorption behavior

Modulating the interaction between small gas molecules and solid host materials is becoming increasingly important for the future society due to the alternative energy resources especially for the hydrogen energy. As is known, two catalogues of materials such as two-dimensional (2D) lamellar cavity structures and three-dimensional (3D) infinite tunnel structures have received intensive considerations during the past decades. Herein, we put forward a new alternative that the solid materials with synergic effects of grain-boundary-rich (GBR) structure and 3D hierarchical hollow structure would also be a promising candidate for modulating the gas molecules in solid adsorbents. As expected, our constructed novel 3D hollow hierarchitectures with GBR shells standing on the hollow spherical cavity indeed resulted in the enhanced hydrogen adsorption behavior. The as-prepared 3D hollow hierarchitectures were very uniform in large scale, and the very simple reaction process offers high convenience, short reaction time, and no need for any complex manipulations or equipments. The hollow outlook of the rutile VO(2)(R) 3D hierarchitectures is the reminiscence of the hollow cavity of nsutite-type VO(2), while the formation of the VO(2)(R) GBR structure is attributed to volume shrink from a unique intergrowth structure of nsutite-type VO(2). The novel gas modulation model with the synergic effect of GBR structure and hierarchical hollow structure may pave a new way for developing materials in energy and environmental fields in the near future.

Synthesis and characterization of activated carbon‐platinum composites and effect on hydrogen storage rate

ABSTRACTA novel, facile and low temperature process for activated carbon‐platinum (AC‐Pt) composites has been developed in the absence of additive reducing agents. By varying the pH value and heating approach, the size and amounts of loading Pt nanoparticles could be tuned. According to the results of nitrogen adsorption analysis, small angle X‐ray scattering profiles, X‐ray diffractometer spectrometer patterns, inductively coupled plasma mass spectrometry and field emission scanning electron microscope images, it was indicated that lower pH value and higher reaction temperature would conduce to larger Pt nanoparticles as well as greater amounts. Attributing to the results of nitrogen adsorption analysis, the impregnating condition of Pt nanocrystals also obviously influenced the specific surface area and the pore structure of AC‐Pt composites, which evidently resulted in dissimilar hydrogen adsorption behavior. In this research, the hydrogen storage rate was measured using high pressure thermo‐gravimetric analyzer under flow condition. It was discovered that small Pt nanoparticles uniformly distributed in pores might aid gas diffusion of hydrogen molecules and surface diffusion of atomic hydrogen in pores of AC via the so‐called hydrogen spillover phenomenon and enhance higher adsorption rate, even at lower Pt contents. © 2011 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Effect of Zn/Co ratio in MOF-74 type materials containing exposed metal sites on their hydrogen adsorption behaviour and on their band gap energy

Simultaneous incorporation of Zn and Co ions into MOF-74 during the crystallization process has been studied, covering the whole Zn/Co concentration range (0–100% Co). The characterization techniques used, including X-ray diffraction, DR-UV-visible spectroscopy, N 2 adsorption isotherms and thermogravimetric analysis, strongly evidence the successful incorporation of both cations into the material framework, producing the crystallization of MOF-74 with 100% Co and MOF-74 with 100% Zn starting from Zn-free and Co-free initial mixtures, respectively, under the same conditions. H 2, CH 4 and CO 2 uptakes of MOF-74 type materials generally increase with framework Co content at any pressure, suggesting a relevant role of cobalt in the adsorption process. As expected, the comparison between the gas adsorption behavior of Co-substituted MOF-5 and Co-containing MOF-74 materials shows that exposed metal sites play a key role in MOF performance in adsorption. On the other hand, the good agreement between the evolution of the experimental band gap values as a function of the Co content and the computational-based predictions found in the literature further supports the coexistence of Zn 2+ and Co 2+ ions forming the MOF-74 metal clusters. Finally, we found that variations of both isosteric heat of hydrogen adsorption and band gap energy with the metal cluster composition show a parallel trend, although it is not systematic in the whole range of Zn/Co ratio. Indeed, a minimum band gap energy value and a maximum isosteric heat of H 2 adsorption value were found to appear simultaneously for Co-rich samples still having some Zn rather than for all-Co samples.

Influence of phosphoric acid treatment on hydrogen adsorption behaviors of activated carbons

The scope of this work investigates the relationship between the amount of oxygen-functional groups and hydrogen adsorption capacity with different concentrations of phosphoric acid. The amount of oxygen-functional groups of activated carbons (ACs) is characterized by X-ray photoelectron spectroscopy. The effects of chemical treatments on the pore structures of ACs are investigated by N2/77 K adsorption isotherms. The hydrogen adsorption capacity is measured by H2 isothermal adsorption at 298 K and 100 bar. In the results, the specific surface area and pore volume slightly decreased with the chemical treatments due to the pore collapsing behaviors, but the hydrogen storage capacity was increased by the oxygen-functional group characteristics of AC surfaces, resulting from enhanced electron acceptor-donor interaction at interfaces.

Hydrogen storage on Ti decorated SiC nanostructures: A first principles study

In the present study we report the hydrogen adsorption behavior of two SiC nanostructures; a planar sheet and a nanotube (10, 0) of 1 nm diameter decorated by Ti atoms on it. All calculations have been performed using a plane-wave based pseudopotential method. The lowest energy structure of the Ti adsorbed SiC sheet shows that Ti atom distorts the sheet in such a way that one of the Si atoms goes down the plane and the Ti atom bind with nearest three C atoms. The interaction of this Ti decorated sheet with hydrogen suggests that each Ti atom can bind up to four hydrogen molecules (all hydrogens are adsorbed in the molecular form) with an average binding energy of 0.37 eV. For SiC nanotube, the adsorption of Ti favors the hexagonal hollow site. Moreover, on interaction of this Ti decorated tube with hydrogen leads to dissociation of the first hydrogen molecule in the atomic form and thereafter adsorbs hydrogen in the molecular form. The average binding energy of hydrogen molecules on this Ti decorated tube is estimated to be 0.65 eV. Based on these results we infer that the Ti decorated SiC nanostructures moderately bind with hydrogen molecules (within the energy window for hydrogen storage materials) and therefore, can be considered as one of the potential hydrogen storage material.

Adsorption and Diffusion of Li and Ni on Graphene with Boron Substitution for Hydrogen Storage: Ab-initio Method

Based on first-principles plane wave calculations, it has been shown that boron-substituted graphene with Li metal atom adsorption can be used as a high-capacity hydrogen storage material. Boron substitution in graphene increases Li and Ni metal adsorption energy, which is much larger than that in pure graphene. The diffusion characteristics of metal atoms were also investigated. The diffusion energy barrier of Ni metal is stronger than that of Li metal, but the cohesive energy of Ni bulk is much larger. Then, the large-scale metal adsorption behavior on boron-substituted graphene was calculated by the molecular dynamics (MD) method. Moreover, hydrogen adsorption behavior on Li metal atoms is investigated. It is found that Li and Ni adatoms dispersed on the double side of graphene can absorb up to eight hydrogen molecules corresponding to 13.2 and 7.9% hydrogen storage capacities, respectively.

Theoretical Prediction of Hydrogen Storage on ZnO Sheet

Using first-principles calculations, we investigate the adsorption behavior of hydrogen on the planar hexagonal ZnO sheet. Our calculations find that the planar ZnO monolayer preferably adsorbs hydrogen molecules, where a hydrogen molecule attaches to one oxygen atom with binding energy of ∼0.13 eV. This implies that the interaction between a hydrogen molecule and the ZnO sheet is stronger than that between a hydrogen molecule and graphene. We predict that each oxygen atom in a ZnO sheet can adsorb two hydrogen molecules on opposite sides of the sheet, and thus the gravimetric density for hydrogen storage on ZnO sheet is evaluated to be about 4.7 wt % at zero temperature. Furthermore, our calculations show that the gravimetric density for hydrogen storage on ZnO sheet reaches 1.5–2.1 wt % at 298 K and 5 MPa. This suggests that, despite their weight, ZnO sheets may have potential applications in hydrogen storage.

Electrochemical properties of palladium adlayers on Pt(1 1 0) substrates

Palladium deposition on Pt(110) electrodes was studied. Differently from Pt(111) and Pt(100), first and further layers cannot be distinguished in this case only through the voltammetric behavior of hydrogen and anion adsorption. The potential of zero total charge (pztc) was determined as a function of the amount of deposited Pd using CO charge displacement experiments and voltammetric curves. The variation of the voltammetric charge due to hydrogen and anion adsorption has been followed during Pd deposition. The voltammetric charge between 0.06 and 0.4V first decreases to a minimum, then increases and finally becomes stable, suggesting that the surface is finally covered with a Pd multilayer. The pztc and CO oxidation charge show similar behavior. CO oxidation, NO reduction and Cu UPD were used as probes to monitor Pd coverage. The potential of CO oxidation increases with Pd coverage while the potential of NO reduction decreases. Using the information obtained from Cu UDP and FTIR experiments it has been possible to determine when the first Pd single layer was completed and when a second (further) layer(s) starts to grow.

Ni(111)上のh-BN薄膜における原子状水素の吸着挙動

Ni(111)上のh-BN薄膜における原子状水素の吸着挙動

Truncated pore network model for the methane and hydrogen adsorption in disordered nanoporous carbons

A useful computational model is described for representing the nanoporous structure in real carbons. The model gathers geometric and topological (e.g. pore connectivity and deadend pores) characteristics and it is used to evaluate the effect that porosity (ɛ) and pore size (H) have on the adsorption behavior of methane and hydrogen (obtained by Grand Canonical Monte Carlo Simulation) quantified in terms of the excess density (ρ) and the gravimetric storage capacity (wt.%). In general higher adsorptions are observed compared to the traditional pore models. An increase in porosity or pore size originates a decrease in ρ. 3.1wt.% is the maximum amount of H2 stored in the material ε=0.40,H=4.89σff at 77K, which is in reasonably good agreement with experimental data. This quantity is lower as the porosity decreases and the pore size increases. The results of this work support some experimental evidences that suggest a linear relation between the hydrogen stored in nanoporous carbons and specific surface area.

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 m 2 g −1) and larger micropore volume (∼0.6 cm 3 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.% H 2 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 H 2 (wt. %) per 500 m 2 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.

Determination of reversible hydrogen adsorption site in Ni-nanoparticle-dispersed amorphous silica for hydrogenseparation at high temperature

The reversible hydrogen adsorption site in Ni-nanoparticle-dispersed amorphous silica (Si-O) was identified by analyzing the hydrogen adsorption behavior and the microstructure. The total amount of reversibly adsorbed hydrogen was evaluated from the total surface area of Ni and the Ni concentration in the composite. The total surface area of the Ni nanoparticles in each sample powder was calculated from the mean particle size of the Ni nanoparticles in the Si-O matrix using dark field images taken by transmission electron microscopy and high-angle annular dark-field images by scanning transmission electron microscopy. The estimated amount of reversibly adsorbed hydrogen was highly consistent with that obtained experimentally by hydrogen adsorption analysis, which suggested that reversible hydrogen adsorption occurred at the Ni/Si-O interface.

Hydrogen Adsorption in Polyoxometalate Hybrid Compounds Based on Porous Metal‐Organic Frameworks

AbstractTwo polyoxometalate hybrid compounds based on porous metal‐organic frameworks (PMOFs/POMs) have been prepared by lithium ion exchange and their crystal structures, stabilities and gas adsorption properties have been characterized. Both compounds consist of neutral Cu3(BTC)2 (BTC = 1,3,5‐benzentricarboxylate) metal‐organic frameworks (MOFs) as hosts and Keggin polyoxometalates (POMs) anions and lithium ions as guests with the MOFs maintaining their permanent porosity. H2 adsorption studies demonstrated that the guests play a key role in increasing the H2 adsorption capacity of the frameworks. With the introduction of POMs and lithium ions, the compounds not only display strong hydrogen adsorption behavior, but also exhibit some differences in H2 binding energy.

High-pressure hydrogen storage on microporous zeolites with varying pore properties

Hydrogen storage on microporous zeolites was examined using a high pressure dose of hydrogen at 30 °C. The roles of the framework structure, surface area, and pore volume of the zeolites on hydrogen adsorption were investigated. The largest hydrogen storage was obtained on the ultra stable Y (USY) zeolite (0.4 wt%). The hydrogen adsorption isotherms on the zeolites reached a maximum after a hydrogen pressure of 50 bar. The amount of hydrogen adsorption on Mordenite (MOR) zeolites increased with increasing Si/Al molar ratio, which was achieved by dealumination. The amount of hydrogen adsorption increased linearly with increasing pore volume of the zeolites. The hydrogen adsorption behavior was found to be dependent mainly on the pore volume of the zeolites.

Coadsorption of hydrogen and CO on well-defined Pt35Ru65/Ru(0001) surface alloys—site specificity vs. adsorbate–adsorbate interactions

The coadsorption of CO and hydrogen on a structurally well-defined Pt(35)Ru(65)/Ru(0001) monolayer surface alloy and, for comparison, on Ru(0001) were investigated by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). The data reveal distinct modifications in the hydrogen adsorption behavior and also in the CO adsorption properties compared to adsorption of the individual components both on the mono-metallic and on the bimetallic surface. These modifications are discussed on an atomic scale, in a picture that involves adsorbate-adsorbate interactions and site-specific variations in the (local) adsorption properties of the bimetallic surface, due to electronic ligand and strain effects and geometric ensemble effects.

Hydrogen adsorption behavior of graphene above critical temperature

We evaluate the hydrogen adsorption behavior of the pristine single-layer graphene sheets in a powder form, which was performed at cryogenic and room temperatures. Only 0.4 wt.% and <0.2 wt.% hydrogen uptake was obtained at 77 K under 100 kPa and room temperature under 6 MPa, respectively, for the pristine graphene sample with a BET specific surface area of 156 m 2 g −1. Structure/property investigations suggest that the low specific surface area and weak binding to hydrogen should be responsible for the small gravimetric uptake of pristine graphene sample.

Molecular dynamics simulation study on the hydrogen adsorption and diffusion in non-interpenetrating and interpenetrating IRMOFs

We performed molecular dynamics simulations at 77 K on the non-interpenetrating isoreticular (having the same underlying topology) metal-organic frameworks (IRMOFs) and the interpenetrating IRMOFs to investigate the adsorption behavior of hydrogen on the surface of MOFs, catenation effect on the density of adsorbed hydrogen, and dynamic behavior of adsorbed hydrogen molecules. We tested two classical force fields, universal force field (UFF) and DREIDING force field for the simulations and found out that the UFF describes the adsorption of hydrogen more reliably than DREIDING force field. The simulations showed the density values of adsorbed hydrogen in the small pores of the interpenetrating IRMOFs are higher than those in the larger pores of the non-interpenetrating IRMOFs, and the diffusion of the hydrogen molecules in the interpenetrating IRMOFs is highly restricted compared to the non-interpenetrating IRMOFs. From the simulation results, we concluded that the small pores created by the catenation might contribute the increase of the adsorption capacity of the interpenetrating IRMOFs.

Interaction of Hydrogen with Bimetallic Surfaces

Abstract The interaction of hydrogen with bimetallic surfaces is assessed and discussed using structurally well defined PdAu and PtRu single crystal surfaces as model systems. The description is based on a correlation between the hydrogen adsorption behavior and the presence and abundance of specific bimetallic nanostructures. The latter are determined quantitatively by high resolution scanning tunneling microscopy. Following the changes in the hydrogen adsorption behavior on surfaces with systematically varied composition and thus varying concentrations of specific structural elements and adsorption ensembles allows a direct correlation between structural and chemical properties and thus to identify the adsorption characteristics of individual adsorption ensembles. This provides a structural basis for parallel theoretical studies, which are essential for a systematic understanding of the complex changes in the adsorption properties.Based on results from experimental studies and calculations, the role of electronic strain and ligand effects, including lateral and vertical ligands, as well the influence of geometric ensemble effects on the hydrogen adsorption characteristics are discussed. The distinct differences between surfaces modified by a monolayer or monolayer islands of a second metal and mixed surfaces such as surface alloys or alloy surfaces are discussed in these terms.