Hydrogen Physisorption Research Articles

Solution-Phase Synthesis of Heteroatom-Substituted Carbon Scaffolds for Hydrogen Storage

This paper reports a bottom-up solution-phase process for the preparation of pristine and heteroatom (boron, phosphorus, or nitrogen)-substituted carbon scaffolds that show good surface areas and enhanced hydrogen adsorption capacities and binding energies. The synthesis method involves heating chlorine-containing small organic molecules with metallic sodium at reflux in high-boiling solvents. For heteroatom incorporation, heteroatomic electrophiles are added to the reaction mixture. Under the reaction conditions, micrometer-sized graphitic sheets assembled by 3-5 nm-sized domains of graphene nanoflakes are formed, and when they are heteroatom-substituted, the heteroatoms are uniformly distributed. The substituted carbon scaffolds enriched with heteroatoms (boron ∼7.3%, phosphorus ∼8.1%, and nitrogen ∼28.1%) had surface areas as high as 900 m(2) g(-1) and enhanced reversible hydrogen physisorption capacities relative to pristine carbon scaffolds or common carbonaceous materials. In addition, the binding energies of the substituted carbon scaffolds, as measured by adsorption isotherms, were 8.6, 8.3, and 5.6 kJ mol(-1) for the boron-, phosphorus-, and nitrogen-enriched carbon scaffolds, respectively.

The effect of temperature and topological defects on H 2 adsorption on carbon nanotubes

Physisorption of molecular hydrogen on pristine single-walled carbon nanotube and three types of topologically defected nanotubes (Stone-Wales, vacancy and interstitial defects) at different temperatures 77, 300 and 600 K has been investigated via molecular dynamics simulation. The interatomic interactions (covalent bonds) between the carbon atoms within the nanotube wall were modeled by the well-known bond order Tersoff potential. The applied intermolecular forces are modeled using the modified form of the well-known Lennard–Jones potential based on the nanotube curvature. The adsorption/desorption cycle was followed by increasing the operating temperature under the pressure of 1 bar. The simulation results of exposing 6.5%wt of H 2 on defected and pristine (3,3) nanotubes reveal that the highest and lowest adsorption energies and storage capacities are obtained from the nanotubes with interstitial and vacancy defects, respectively.

Electrochemical Hydrogen Adsorption and Absorption. Part 1: Under-potential Deposition of Hydrogen

The review article presents an atomic-level discussion of the fundamental steps involved in hydrogen electro-adsorption on transition-metal electrodes. It also discusses the basic events involved in hydrogen physisorption and chemisorption under low-pressure gas-phase conditions in order to identify characteristics that are unique to the electrochemical environment. The electrochemical environment that comprises the solid electrode, the liquid electrolyte solution, and the electrostatic field creates favorable conditions for the electro-adsorption of two different hydrogen species, the under-potential and over-potential adsorbed hydrogen (HUPD and HOPD). The electro-adsorption of HUPD and HOPD occurs in two different potential ranges. The electro-adsorption of HUPD is characteristic of Pt group metals only, while the electro-adsorption of HOPD takes place at all electrode materials at which H2(g) can be electrolytically generated. The existence of HUPD and HOPD is supported by spectroscopic and thermodynamic results. A thermodynamic analysis of the electro-adsorption of HUPD results in the determination of thermodynamic state functions that govern the process, namely the standard Gibbs energy, enthalpy and entropy of electro-adsorption, $$ {\Delta_{{\rm{ec - ads}}}}G^\circ \left( {{{\hbox{H}}_{\rm{UPD}}}} \right) $$ , $$ {\Delta_{{\rm{ec - ads}}}}H^\circ \left( {{{\hbox{H}}_{\rm{UPD}}}} \right) $$ , and $$ {\Delta_{{\rm{ec - ads}}}}S^\circ \left( {{{\hbox{H}}_{\rm{UPD}}}} \right) $$ , the Gibbs energy of later interactions, $$ \omega \left( {{{\hbox{H}}_{\rm{UPD}}}} \right) $$ , and the M–HUPD surface bond energy, $$ E^\circ \left( {{\hbox{M}} - {{\hbox{H}}_{\rm{UPD}}}} \right) $$ . Thermodynamic data for the electro-adsorption of HUPD on polycrystalline electrodes (Pt(poly) and Rh(poly)) and on Pt(111) in several aqueous electrolyte (H2SO4, HClO4, and NaOH) solutions are reported. Their analysis and the analysis of $$ {\Delta_{{\rm{ec - ads}}}}H^\circ \left( {{{\hbox{H}}_{\rm{UPD}}}} \right) $$ and $$ E^\circ \left( {{\hbox{M}} - {{\hbox{H}}_{\rm{UPD}}}} \right) $$ allow us to compare on a thermodynamic basis HUPD to Hchem, and to identify surface adsorption sites possibly occupied by HUPD and HOPD adatoms.

Hydrogen physisorption in metal–organic frameworks: concepts and quantum chemical calculations

Storage of hydrogen by physisorption in metal–organic frameworks is reviewed from the perspective of quantum chemistry. Concepts regarding the interaction of hydrogen with metals are revised and the specific features of metal–organic frameworks are explained. The influence of the type of inorganic cluster and hydrogen loading and its relation to hydrogen storage are analysed. Heats of hydrogen adsorption in previous studies are critically discussed and estimations are made regarding the adsorption strength needed for storage applications and how to approach commercial targets.

Effect of piezoelectric material on hydrogen adsorption

In hydrogen storage applications, the primary issue for physisorption of hydrogen onto solid-state materials is the weak interaction force between hydrogen molecules and the adsorbents. It is found that enhanced adsorption can be obtained under an external electric field, because it appears the electric field increases the hydrogen adsorption energy. Experiments were carried out to determine hydrogen adsorption on activated carbon using the piezoelectric material PMN–PT as the charge supplier under hydrogen pressure. Results indicate that more than 20% hydrogen adsorption enhancement was obtained. Parameters related to hydrogen adsorption enhancement include the amount of the charge and temperature. Higher voltage and lower temperature promote the increase of adsorption capacity but room temperature results are very encouraging.

First principles study of the physisorption of hydrogen molecule on graphene and carbon nanotube surfaces adhered by Pt atom

Adsorptions of hydrogen, oxygen and carbon monoxide molecules on surfaces of single wall carbon nanotubes (SWNTs) and graphene adhered by a Pt atom have been investigated by density functional theory calculation (DFT). Our calculations show that the Pt adatom significantly promotes the physisorption of hydrogen in a region around it with radius of about 5 Å . The physisorption configuration in which oxygen molecule aligned parallelly to the surfaces of SWNTs and graphene are most preferred. In contrast, both of the physisorption configurations in which CO molecule aligned parallelly and perpendicularly with the carbon end towards the graphene and SWNTs surfaces were preferred. The obtained results suggested that the modification of the electronic structure by adhesion of Pt atom on surfaces of the support materials can modify their physisorption properties of gas molecules.

New Chiral and Flexible Metal−Organic Framework with a Bifunctional Spiro Linker and Zn4O-Nodes

A new chiral Metal-Organic Framework (MOF), named DUT-7, has been synthesized from enantiopure (S)-2,2'-spirobiindane-5,5'-dicarboxylic acid ((S)-H(2)L) and zinc nitrate. The framework of the compound has the composition Zn(4)O((S)-L)(3) as it is found for the IRMOF series, but in contrast to these MOFs, the crystal structure of DUT-7(RT) (RT: room temperature) which has to be assigned to the chiral space group P6(3)22, has a completely different topology. The Zn(4)O clusters are not coordinated in an octahedral fashion but show only C(3) symmetry and are arranged in a trigonal-prismatic manner. The framework is built of two interpenetrated nets with an acs topology related to each other by the 2-fold axes. DUT-7 is the first example of this rare framework topology constructed from Zn(4)O units. A reversible structural transformation was observed upon cooling during single crystal X-ray diffraction. The resulting crystal structure, denoted as DUT-7(LT) (LT: low temperature), is characterized by a Zn(4)O cluster not only coordinated by six linker moieties but also by two additional solvent molecules leading to an octahedral coordination of one of the zinc atoms of the cluster. This structure transformation leads to a tripled unit cell compared to DUT-7(RT) and a change of the space group to P6(5)22. The flexibility of the coordination of the metal atoms which has been observed for the first time points toward a catalytic activity of MOFs exhibiting metal atoms with a closed shell not only caused by defects in the crystal structure. The reaction of racemic 2,2'-spirobiindane-5,5'-dicarboxylic acid (rac-H(2)L) with zinc nitrate lead to a microcrystalline compound DUT-7(rac). DUT-7 and DUT-7(rac) have been characterized by X-ray powder diffraction, elemental and thermogravimetric analysis, and IR spectroscopy revealing the same framework composition for both compounds. The porosity of DUT-7 and DUT-7(rac) was proven by nitrogen and hydrogen physisorption measurements.

Wind-hydrogen energy stand-alone system with carbon storage: Modeling and simulation

A wind-hydrogen hybrid system with carbon physisorption storage has been developed and implemented within a dynamic model-based software environment. Numerical simulations have been applied to synthetic and real data to evaluate its operations and performance over a 6-months period. Hydrogen is yielded by electrolysis with energy converted from wind, and load is powered either by direct turbine connection, by battery or a fuel cell. Surplus hydrogen is stored by physisorption in a cluster of nitrogen-cooled tanks filled with activated carbons. Physisorption has been modeled after the Ono-Kondo isotherm from laboratory data available in literature. The operating cycle is composed of four transformations: isobar pre-charging at 0.1 MPa, isothermal charging at 77 K, isobar pre-discharging at 6 MPa, and isothermal discharging at 153 K. From our simulation runs, the system can operate as stand-alone granting total independence from the grid. The storage system has good gravimetric and volumetric capacity (10.8% and 32.5 g/l at 6 MPa). Overall system efficiency is estimated to be around 10%. Hydrogen physisorption on carbon seems a potentially feasible storage technique for hydrogen with tanks that are compact and safe, hence apt for stationary and some non-stationary applications.

Hydrogen storage in BC3 composite single-walled nanotube: a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory (DFT) and grand canonical Monte Carlo simulations (GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC3 nanotubes and carbon nanotubes. The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes. Furthermore, the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions. The present results have shown that with both computational methods, the hydrogen storage capacity of BC3 nanotubes is superior to that of carbon nanotubes. The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.

Easy γ-to-α transformation of zirconium phosphate/polyphenylphosphonate salts: Porosity and hydrogen physisorption

Abstract The preparation of organic–inorganic materials based on the topotactic exchange reactions of the γ phase of zirconium phosphate and polyphenyl bisphosphonates is reported. The treatment of these materials with hypophosphoric, phosphorous and methylphosphonic acids easily led to an isomerization of the γ phases to their α allotropes. These reactions rendered finely engineered supramolecular structures by means of mild, simple processes performed in the solid–liquid interface. This kind of clean γ-to-α transformations described in our work has few precedents in the literature and allows for the effortless preparation of libraries of similar materials in which the testing of a given set of properties versus subtle structural changes may be easily performed. Using this rationale we have produced materials able to store up to 1.7% (w/w) of H 2 at 77 K and 1 atm with such high ultramicroporosity that the DOE-goal H 2 densities established for 2010 could be complied at pressures well below 5 atm.

Hydrogen sorption in transition metal modified mesoporous materials

Ni, Rh and Pd incorporated mesoporous MCM-41, MCM-48, HMS and SBA-15 samples were synthesized and were characterized using XRD, ICP/EDX and N 2 adsorption–desorption at 77.4 K. The hydrogen adsorption studies in the synthesized materials were performed at 77.4 K (up to 112 kPa) and 303 K (up to 4000 kPa). The hydrogen adsorption isotherms of pristine and transition metals incorporated mesoporous materials at 77.4 K were completely reversible reflecting physisorption of hydrogen in these materials. The hydrogen adsorption isotherms at 303 K were not reversible showing the chemisorption of hydrogen in these materials at 303 K. Hydrogen sorption studies showed that transition metal modification improved the hydrogen storage capacity of mesoporous materials at 303 K. The desorption of the adsorbed hydrogen by heating up to 500 K from the mesoporous materials were also carried out for studying the recovery of adsorbed hydrogen from transition metal incorporated mesoporous materials.

Influence of structural heterogeneity of nanoporous sorbent walls on hydrogen storage

Heterogeneity is an ubiquitous aspect of adsorption, often modifying substantially the observed behaviour of the adsorbate–adsorbent system. In this paper, the influence of heterogeneity is explicitly analyzed for the case of the adsorption of molecular hydrogen onto nanoporous carbon. Grand Canonical Monte Carlo simulations were used to study the mechanism of adsorption in the models of the adsorbate that include both energetic and structural modifications of graphene-based slit pores. In particular, a partial substitution of carbons by boron modifies both the symmetry of the energy landscape and the strength of hydrogen physisorption; which results in considerable increases of the amount of adsorbed gas without major modification of the mechanism of adsorption. Additional heterogeneity arises from structural modifications of the adsorbent by neutron irradiation of boron-doped samples, where the boron fission products generate additional surface area for adsorption. Simulations of adsorption in such pores show that hydrogen uptake is strongly dependent on the chemical nature of the modified pore walls.

Open space for the physisorption of H 2: Cointercalation of graphite with Li, Ti metal atoms and ethylene molecules

Based on first-principles plane-wave calculations, we explored the method with the ethylene molecules and Ti, Li atoms intercalated into the graphite to open space for the physisorption of hydrogen. And our simulation indicated that the interlayer distance of the graphene is close to the optimal physisorption of hydrogen with this method. From our computation, we got that the type of 3 × 3 supercell has the lowest converge energy and is energetically favorable. The energy barrier of changing the type of 2 × 2 supercell to 3 × 3 supercell is high.

First-principle study of interaction of molecular hydrogen with BC3 composite single-walled nanotube

The physisorption of molecular hydrogen in BC3 composite single-walled nanotube, investigated using density functional theory, was compared with single-walled carbon nanotube. Both external and internal adsorption sites of these two nanotubes have been studied with the hydrogen molecular axis oriented parallel to the nanotube wall. The calculated results show that: ([see full textsee full text]) the physisorption energies of a H2 molecule are larger for BC3(8,0) composite nanotube than for C(8,0) nanotube at all adsorption sites examined. ([see full textsee full text]) For these two nanotubes, the physisorption energies are larger for hydrogen bound inside the nanotubes than for adsorption outside the nanotubes. The different behavior between these two nanotubes is explained by the contour plots of electron density and charge-density difference of them. The present computations suggest that BC3 nanotube may be a better candidate for hydrogen storage than carbon nanotube.

Enhanced hydrogen sorption on carbonaceous sorbents under electric field

The effect of an applied electric field on hydrogen physisorption isotherm on carbonaceous sorbents was studied. Distinctive sorption enhancement was obtained by applying a positive electrical potential of 2000 V to platinum-supported carbon samples. The phenomenon was ascribed to stronger interactions between hydrogen and the sorbent. Theoretical studies suggested that, the interaction between hydrogen and neutral carbon is primarily the electrostatic attraction between the π-bonds of the aromatic rings and the σ-bonds of H 2, which is classified as van der Waals interaction and is weak. However, the interaction between electrically charged carbon and hydrogen might involve orbital interactions between hydrogen and carbon, an interaction stronger than van der Waals attraction. Experimental studies indicated that the presence of platinum would induce dissociation of hydrogen molecules in to hydrogen atoms. The easier accessibility of the atomic orbital might favor the electron transfer from the atomic hydrogen to charged carbon.

Influence of sample cell physisorption on measurements of hydrogen storage of carbon materials using a Sieverts apparatus

In recent years, large fluctuations have been reported for measurements of the hydrogen storage of carbon materials using a Sieverts apparatus. To investigate this problem, helium gas adsorption was selected for comparison with the adsorption of hydrogen, and the results show that hydrogen but not helium was adsorbed onto the wall of the sample cell at ambient temperature. The adsorption capacity of the sample cell at 77 K is higher than that at ambient temperature. A series of adsorption tests was conducted with a LaNi 5 alloy to prove the influence of the physisorption, and the results show that an increase in the hydrogen storage capacity was resulted in when sample loading decreases. After correction for this hydrogen physisorption, the capacity was restricted between 1.38 and 1.41 wt.%. Multi-walled carbon nanotubes (MWCNTs), activated carbon (AC), single-walled carbon nanotubes (SWCNTs), graphite nanofibers (GNFs), and graphite oxide (GO) were also measured and corrected through this method.

Synthesis of Micro-Porous Boron-Substituted Carbon (B/C) Materials Using Polymeric Precursors for Hydrogen Physisorption

This paper discusses a novel route to prepare porous boron substituted carbon (B/C) materials that show a significantly higher hydrogen binding energy and physisorption capacity, compared with the corresponding carbonaceous (C) materials. The chemistry involves a designed boron-containing polymeric precursor, which is the polycondensation adducts between BCl3 and lithiated phenylene diacetylene. During pyrolysis, most of the boron moieties in the precursor were transformed into a B-substituted C fused ring structure, and the in situ formed LiCl by-products created a porous morphology. The resulting porous B/C material with 7% B content and 700 m2/g surface area has been prepared, which shows a reversible hydrogen physisorption capacity of 0.6 and 3.2 wt% at 293 and 77 K, respectively, under 40 bars hydrogen pressure. The physisorption results were further warranted by absorption isotherms and in situ 1H NMR studies, indicating a binding energy of hydrogen molecules of about 11 kJ/mole, significantly higher than the 4 kJ/mole reported on most C surfaces

Electric field induced reversible switch in hydrogen storage based on single-layer and bilayer graphenes

In an ideal hydrogen storage system, binding strength should increase during adsorption whereas the opposite should be the case during desorption. These two seemingly contradictory requirements limit the types of systems that can be utilized. Density-functional theory (DFT) calculations are carried out to investigate hydrogen physisorption on Li-doped single-layer and bilayer graphenes. We propose that the superimposition of an electric field can be used to effectively control hydrogen adsorption. More specifically, we report that hydrogen binding can be enhanced under a positive electric field, whereas it can be weakened under a negative electric field. Our results show that the binding strength increases by 88% when a field with a magnitude of +0.020 au is imposed. Hirshfeld charge analysis results suggest that an increase in the binding strength will occur as long as the Li (or C) carries more positive (or negative) charges. Our calculations demonstrate that, in the case of Li-doped graphene, the application of a positive electric field yields an increase in binding strength during adsorption while a negative field decreases the binding strength during desorption.

Prediction of energetically optimal single-walled carbon nanotubes for hydrogen physisorption

Hydrogen storage by carbon nanotubes (CNTs) is a challenging issue still in debate. Using an approximate density functional method augmented with a van der Waals dispersion term, we have shown that there are binding maxima for H2/single-walled carbon nanotube (SWCNT) complexes at (5, 5) and (8, 0) tubes for armchair and zigzag CNTs, respectively, with binding energies around three times as large as that of H2 on graphene surface. We predict that SWCNTs with diameters of 6–7 Å are energetically optimal candidates for physisorption of molecular hydrogen.

Highly Porous Metal-Organic Framework Containing a Novel Organosilicon Linker − A Promising Material for Hydrogen Storage

The synthesis and characterization of the new metal-organic framework PCN-12-Si (isoreticular to PCN-12) is reported. PCN-12-Si comprises dicopper paddle-wheel units located at the vertices of a cuboctahedron, which are connected by the new linker 5,5'-(dimethylsilanediyl)diisophthalate (dmsdip). The microporous MOF has a high specific surface area of S(BET) = 2430 m(2) g(-1) and a high specific micropore volume of V(p) = 0.93 cm(3) g(-1) (p/p(0) = 0.18). The activated form of PCN-12-Si shows a remarkable hydrogen storage capacity. Volumetric low pressure hydrogen physisorption isotherms at 77 K reveal an uptake of 2.6 wt % H(2) at 1 bar. Furthermore, results of theoretical GCMC simulations of hydrogen adsorption are presented. The simulated low pressure isotherm is in excellent agreement with the experimental one. Simulations for the high pressure regime predict an excess hydrogen uptake of 4.8 wt % at 30 bar, which corresponds to an absolute amount adsorbed of 5.5 wt %. In addition, the potential field of H(2) inside PCN-12-Si was derived from the simulations and analyzed in detail, providing valuable insights concerning the preferred adsorption sites on an atomic scale.