H2 Uptake Research Articles

Coupling amino acid L-Val with THF for superior hydrogen hydrate kinetics: Implication for hydrate-based hydrogen storage

Hydrogen (H2) emerges as a promising future clean energy for the low-carbon and sustainable future due to its high energy density and no pollutant or greenhouse gas emissions after combustion. The advantage of H2 storage in solid-hydrate form is the requirement of only moderate pressure and temperature compared to compressed H2 storage and the relatively lower energy consumption compared to liquid H2 storage. However, the slow kinetics of H2 hydrate formation is one major challenge to breakthrough for the large-scale development of hydrate-based H2 storage. In this study, we introduced an environmental-benign kinetic promoter (L-valine, L-Val) and coupled it with a thermodynamic promoter tetrahydrofuran (THF) using stoichiometric concentration (5.56 mol%) to enhance H2 hydrate formation kinetics. 0.3 wt% L-Val coupled with 5.56 mol% THF yields the optimal kinetic enhancement, and the maximum volumetric H2 uptake (VH2) is 29.83 ± 1.22 volume of H2/volume of H2-THF hydrate (v /v). The reusability of L-Val is proved in five consecutive cycles of H2-THF hydrate formation and dissociation with consistently superior H2 uptake. Furthermore, it was identified that cooling rate (Rc) was an important factor determining the H2-THF hydrate formation kinetics. Lower Rc (0.05 K/min) shows an optimal promoting effect of VH2, which was 105.29% higher than that at higher Rc (0.3 K/min). A mechanism is proposed to explain the effect of Rc on H2-THF hydrate formation kinetics. The maximum gravimetric H2 (GH2) reported in our study reaches 0.26 ± 0.01 wt%, which was superior in current literature below 15.0 MPa. The results provide insights into speeding up H2 uptake in solid-hydrate form and have potential applications in hydrate-based hydrogen storage.

Investigation of hydrogen adsorption sites in ferrocene-based hypercrosslinked polymers by DFT calculations

Herein, two types of Fc-based hypercrosslinked polymers (HHCP and DHCP) with high BET surface area (953.9 and 1062.7 m2 g−1) were prepared by direct one-step phenolic polycondensation aiming at high uptake capacity towards H2. As expected, the hydrogen uptake values of HHCP and DHCP were notably higher than those of porous polymers with a higher surface area under the same conditions. The maximum H2 uptake of HCPs at 77 K/1.0 bar are determined to be 2.51 wt % for HHCP and 2.74 wt % for DHCP, respectively. Despite the pore structure playing a determinant role in hydrogen adsorption, the adsorption sites in the polymer framework can be another essential factor to influence the hydrogen adsorption capacity. The interactions between the Fc building block and H2 are revealed by DFT calculation to fully illustrate the role of Fc in H2 adsorption. The results indicate that both iron atoms and benzene rings in Fc-based HCPs contribute to the adsorption of hydrogen. Moreover, it is interesting to find that the most stable adsorption site around the Fc building unit is the position directly above the Cp ring. The results in this work may more reasonably explain the phenomenon that the introduction of Fc units could enhance the adsorption of H2 in many studies, which also provides possible insights into the application of metallocene compounds in H2 adsorption.

Downscaling Industrial-Scale Syngas Fermentation to Simulate Frequent and Irregular Dissolved Gas Concentration Shocks.

In large-scale syngas fermentation, strong gradients in dissolved gas (CO, H2) concentrations are very likely to occur due to locally varying mass transfer and convection rates. Using Euler-Lagrangian CFD simulations, we analyzed these gradients in an industrial-scale external-loop gas-lift reactor (EL-GLR) for a wide range of biomass concentrations, considering CO inhibition for both CO and H2 uptake. Lifeline analyses showed that micro-organisms are likely to experience frequent (5 to 30 s) oscillations in dissolved gas concentrations with one order of magnitude. From the lifeline analyses, we developed a conceptual scale-down simulator (stirred-tank reactor with varying stirrer speed) to replicate industrial-scale environmental fluctuations at bench scale. The configuration of the scale-down simulator can be adjusted to match a broad range of environmental fluctuations. Our results suggest a preference for industrial operation at high biomass concentrations, as this would strongly reduce inhibitory effects, provide operational flexibility and enhance the product yield. The peaks in dissolved gas concentration were hypothesized to increase the syngas-to-ethanol yield due to the fast uptake mechanisms in C. autoethanogenum. The proposed scale-down simulator can be used to validate such results and to obtain data for parametrizing lumped kinetic metabolic models that describe such short-term responses.

Engineering Pore Environments of Sulfate-Pillared Metal-Organic Framework for Efficient C2 H2 /CO2 Separation with Record Selectivity.

Engineering pore environments exhibit great potential in improving gas adsorption and separation performances but require specific means for acetylene/carbon dioxide (C2 H2 /CO2 ) separation due to their identical dynamic diameters and similar properties. Herein, a novel sulfate-pillared MOF adsorbent (SOFOUR-TEPE-Zn) using 1,1,2,2-tetra(pyridin-4-yl) ethene (TEPE) ligand with dense electronegative pore surfaces is reported. Compared to the prototype SOFOUR-1-Zn, SOFOUR-TEPE-Zn exhibits a higher C2 H2 uptake (89.1 cm3 g-1 ), meanwhile the CO2 uptake reduces to 14.1 cm3 g-1 , only 17.4% of that on SOFOUR-1-Zn (81.0 cm3 g-1 ). The high affinity toward C2 H2 than CO2 is demonstrated by the benchmark C2 H2 /CO2 selectivity (16 833). Furthermore, dynamic breakthrough experiments confirm its application feasibility and good cyclability at various flow rates. During the desorption cycle, 60.1 cm3 g-1 C2 H2 of 99.5% purity or 33.2 cm3 g-1 C2 H2 of 99.99% purity can be recovered by stepped purging and mild heating. The simulated pressure swing adsorption processes reveal that 75.5 cm3 g-1 C2 H2 of 99.5+% purity with a high gas recovery of 99.82% can be produced in a counter-current blowdown process. Modeling studies disclose four favorable adsorption sites and dense packing for C2 H2 .

Boronation of Biomass-Derived Materials for Hydrogen Storage

In spite of the widespread range of hydrogen applications as one of the greenest energy vectors, its transportation and storage still remain among the main concerns to be solved in order to definitively kickstart a rapid takeoff of a sustainable H2 economy. The quest for a simple, efficient, and highly reversible release storage technique is a very compelling target. Many studies have been undertaken to increase H2 storage efficiency by exploiting either chemisorption or physisorption processes, or through entrapment on different porous solid materials as sorbent systems. Among these, biomass-derived carbons represent a category of robust, efficient, and low-cost materials. One question that is still open-ended concerns the correlation of H2 uptake with the kind and number of heteroatoms as dopant of the carbonaceous sorbent matrix, such as boron, aiming to increase whenever possible bonding interactions with H2. Furthermore, the preferred choice is a function of the type of hydrogen use, which may involve a short- or long-term storage option. In this article, after a brief overview of the main hydrogen storage methods currently in use, all the currently available techniques for the boronation of activated carbonaceous matrices derived from recycled biomass or agricultural waste are discussed, highlighting the advantages and drawbacks of each of them.

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.

Hydrogen Storage on Porous Carbon Adsorbents: Rediscovery by Nature-Derived Algorithms in Random Forest Machine Learning Model

Porous carbons as solid adsorbent materials possess effective porosity characteristics that are the most important factors for gas storage. The chemical activating routes facilitate hydrogen storage by adsorbing on the high surface area and microporous features of porous carbon-based adsorbents. The present research proposed to predict H2 storage using four nature-inspired algorithms applied in the random forest (RF) model. Various carbon-based adsorbents, chemical activating agents, ratios, micro-structural features, and operational parameters as input variables are applied in the ML model to predict H2 uptake (wt%). Particle swarm and gray wolf optimizations (PSO and GWO) in the RF model display accuracy in the train and test phases, with an R2 of ~0.98 and 0.91, respectively. Sensitivity analysis demonstrated the ranks for temperature, total pore volume, specific surface area, and micropore volume in first to fourth, with relevancy scores of 1 and 0.48. The feasibility of algorithms in training sizes 80 to 60% evaluated that RMSE and MAE achieved 0.6 to 1, and 0.38 to 0.52. This study contributes to the development of sustainable energy sources by providing a predictive model and insights into the design of porous carbon adsorbents for hydrogen storage. The use of nature-inspired algorithms in the model development process is also a novel approach that could be applied to other areas of materials science and engineering.

Theoretical and Experimental Assessments of Elementary Steps and Bound Intermediates in Catalytic H2–O2 Reactions on Dispersed Pt Nanoparticles

Kinetic and isotopic data and H2 chemisorption uptakes measured under reaction conditions are combined here with theoretical assessments on model catalytic surfaces at relevant hydrogen (H*) coverages to establish the identity and kinetic relevance of elementary steps and bound species in H2–O2 reactions on Pt surfaces. Turnover rates are proportional to O2 pressure and decrease and then reach constant values as H2 pressures increase, leading to apparent first-order rate parameters (rO2/PO2) that reflect reactive collision probabilities of O2 with surfaces and which depend solely on the H2 pressure at all temperatures (540–680 K). H2–D2 isotopic exchange rates during reactions with O2 are much faster than water formation rates, consistent with quasi-equilibrated H2 dissociation steps and with prevalent H* coverages that can be determined independently from H2 uptakes; such measurements enable the decoupling of non-Langmuirian adsorption parameters from kinetic parameters in rate equations. These data indicate that H2–O2 reactions involve two kinetically-relevant O2 dissociation routes. One channel forms two bound O atoms on bare Pt atom ensembles available within H* adlayers, which react via fast subsequent reactions with H* to form H2O. A parallel O2 dissociation route involves reactions with a H*–H* pair to form weakly bound adsorbed hydrogen peroxide (*HOOH*), a highly reactive species that subsequently cleaves its O–O bond in steps that are not kinetically-relevant. The free-energy barriers are dominated by losses in translational entropy incurred upon the formation of the transition states from their gaseous O2 precursors. Kinetic isotope effects are near unity for both routes because H* is not involved in direct O2 dissociation steps, and the *HOOH* formation transition state occurs very early along the reaction coordinate (with nearly intact O–O and Pt–H bonds from reactant states), as confirmed by DFT-derived energies and isotope effects.

Tetranuclear CuII Cluster as the Ten Node Building Unit for the Construction of a Metal-Organic Framework for Efficient C2 H2 /CO2 Separation.

Rational design of high nuclear copper cluster-based metal-organic frameworks has not been established yet. Herein, we report a novel MOF (FJU-112) with the ten-connected tetranuclear copper cluster [Cu4 (PO3 )2 (μ2 -H2 O)2 (CO2 )4 ] as the node which was capped by the deprotonated organic ligand of H4 L (3,5-Dicarboxyphenylphosphonic acid). With BPE (1,2-Bis(4-pyridyl)ethane) as the pore partitioner, the pore spaces in the structure of FJU-112 were divided into several smaller cages and smaller windows for efficient gas adsorption and separation. FJU-112 exhibits a high separation performance for the C2 H2 /CO2 separation, which were established by the temperature-dependent sorption isotherms and further confirmed by the lab-scale dynamic breakthrough experiments. The grand canonical Monte Carlo simulations (GCMC) studies show that its high C2 H2 /CO2 separation performance is contributed to the strong π-complexation interactions between the C2 H2 molecules and framework pore surfaces, leading to its more C2 H2 uptakes over CO2 molecules.

Melamine assisted preparation of nitrogen doped activated carbon from sustainable biomass for H2 and CO2 storage

Activated carbon (AC), as an effective solid adsorbent, is extensively employed in H2 and CO2 storage. To enhance its adsorption capability and selectivity, it is necessary to increase its surface area and dope heteroatoms by a simple and environment-friendly method. In this work, nitrogen doped activated carbon (NAC) has been synthesized from sustainable biomass by direct activation with the assistance of melamine. The obtained NAC with 2.1 wt% N dopants possesses a high surface area (2477.27 m2/g) and pore volume (1.93 cm3/g). The NAC displayed enhanced H2 uptake capacity (2.29 wt% at 77 K, 1 bar and 0.83 wt% at 298 K, 100 bar) and adequate CO2 uptake capacity (2.85 mmol/g at 298 K, 1 bar and 4.49 mmol/g at 273 K, 1 bar). Activation mechanism with the assistance of melamine was proposed in accordance with the experimental data. The facile method of preparing NAC is potential for large-scaled production.

Novel Liquid Organic Hydrogen Carriers with High Hydrogen Performance: NPhCZ/18H-NPhCZ

Exploring the potential liquid organic hydrogen carriers (LOHCs) with high efficiency can promote the advancement of hydrogen storage technology. In this work, a new LOHC member of the carbazole family, perhydro-N-phenylcarbazole (18H-NPhCZ), was first proposed for its high theoretical hydrogen storage capacity (6.9 wt %) and available dehydrogenation reaction enthalpy (ΔrHm(d)⊖ = 51.68 kJ/molH2) based on theoretical calculations. The hydrogenation and dehydrogenation performances were evaluated and exhibited high efficiency in the optimized reaction conditions. The results indicated that 4.74 wt % of H2 was released from 18H-NPhCZ dehydrogenation within 15 min. The combination of experiments and density functional theory (DFT) calculations was employed to investigate the possible intermediates and H2 uptake and release mechanisms. It was found that the elementary reaction from 6H-NPhCZ to NPhCZ was regarded as the rate-limiting step. Furthermore, to balance the storage hydrogen capacity and liquid state at room temperature, a brand-new MIX-LOHC hydrogen storage system (18H-M-B2P1, 6.44 wt %) containing both 18H-NPhCZ and perhydro-dibenzyltoluene (18H-DBT) was successfully proposed as well. It achieved an almost 100% of H2 uptake for 4–6 h and a practical H2 release amount of 6.08 wt % for 10 h. The efficient cycle cohydrogenation and codehydrogenation measurements after 160 h also suggested the stability and reliability of the applications in the hydrogen storage field.

Correlations between H2 Permeation and Physical/Mechanical Properties in Ethylene Propylene Diene Monomer Polymers Blended with Carbon Black and Silica Fillers.

H2 permeation in peroxide-crosslinked EPDM blended with carbon black (CB) and silica fillers was studied at pressures ranging from 1.2 MPa to 90 MPa via the volumetric analysis technique. H2 uptake in the CB-filled EPDM revealed dual-sorption behaviors via Henry's law and the Langmuir model, which were attributed to H2 absorption by the polymer chains and H2 adsorption at the filler interfaces, respectively. Additionally, single-sorption mechanisms were observed for neat EPDM and silica-blended EPDM according to Henry's law, indicating H2 absorption by the polymer chain. The linear decreases in the diffusivity with filler content for the silica-blended EPDMs were attributed to increases in the diffusion paths caused by the filler. Exponential decreases in the diffusivity with increasing filler content and in the permeation with the physical/mechanical properties for CB-filled EPDMs were caused by decreases in the fractional free volume due to increased densities for the EPDM composites. Moreover, good filler-dependent correlations between permeability and density, hardness, and tensile strength were demonstrated for EPDMs used as sealing materials for O-rings. From the resulting equation, we predicted the permeation value without further measurements. Thus, we can select EPDM candidates satisfying the permeation guidelines used in hydrogen infrastructure for the future hydrogen economy.

Concurrent Enhancement of Acetylene Uptake Capacity and Selectivity by Progressive Core Expansion and Extra-Framework Anions in Pore-Space-Partitioned Metal-Organic Frameworks.

A multi-stage core-expansion method is proposed here as one component of the integrative binding-site/extender/core-expansion (BEC) strategy. The conceptual deconstruction of the partitioning ligand into three editable parts draws our focus onto progressive core expansion and allows the optimization of both acetylene uptake and selectivity. The effectiveness of this strategy is shown through a family of eight cationic pore-partitioned materials containing three different partitioning ligands and various counter anions. The optimized structure, Co3 -cpt-tph-Cl (Hcpt=4-(p-carboxyphenyl)-1,2,4-triazole, H-tph=(2,5,8-tri-(4-pyridyl)-1,3,4,6,7,9-hexaazaphenalene) with the largest surface area and highest C2 H2 uptake capacity (200 cm3 /g at 298 K), also exhibits (desirably) the lowest CO2 uptake and hence the highest C2 H2 /CO2 selectivity. The successful boost in both C2 H2 capacity and IAST selectivity allows Co3 -cpt-tph-Cl to rank among the best crystalline porous materials, ionic MOFs in particular, for C2 H2 uptake and C2 H2 /CO2 experimental breakthrough separation.

De-Linker-Enabled Exceptional Volumetric Acetylene Storage Capacity and Benchmark C2H2/C2H4 and C2H2/CO2 Separations in Metal-Organic Frameworks.

An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal-organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M = Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C2H2 uptake capacity under low and ambient pressures (175.3 cm3 cm-3 @ 0.1 bar, 222.9 cm3 cm-3 @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C2H2/C2H4, 22.7 for C2H2/CO2). Remarkably, SNNU-98-Mn can efficiently separate C2H2 from C2H2/CO2 and C2H2/C2H4 mixtures with a benchmark C2H2/C2H4 (1/99) breakthrough time of 2325 min g-1, and produce 99.9999% C2H4 with a productivity up to 64.6 mmol g-1, surpassing values of reported MOF adsorbents.

Microporous polynorbornenes bearing carbocyclic substituents: Structure-property study

Four sets of polymers from norbornene-type monomers with various carbocyclic groups were prepared to perform the structure-property study and to evaluate the effect of main- and side-chains on the porosity of resultant polymers. As monomers, norbornenes with phenyl-, cyclohexyl-, norbornyl-, and framed carbocyclic-groups were designed and synthesized using the Diels-Alder reaction in good yields. All these monomers were involved in ring-opening metathesis and vinyl-addition polymerization to form polymers with various structure of main-chains. The porosity was investigated with help of low temperature nitrogen adsorption/desorption method, and the sorption of H2, CO2, CH4 were also assessed for the most promising synthesized polymers. The obtained polymers exhibited large BET surface areas (up to 740 m2/g), while CO2 and H2 uptake reached 3.0 and 0.18 mmol/g, correspondingly. The porosity of polymers was shown to be determined by the nature of both backbones and side-chains, and it seems that the influence of side-chains is the main one. The largest values of BET surface areas were achieved for polynorbornenes with framed carbocyclic groups. At the same time, vinyl-addition polynorbornenes, which have more rigid main-chains, also provided larger BET surface areas compared to isomeric metathesis ones. Therefore, new valuable relationships between polymer structure and its porosity were established, and an efficient strategy to readily available soluble microporous polymers from norbornene derivatives was suggested. The combination of comparatively simple synthesis, high porosity and solubility in organic solvents can be considered as a key advantage of the synthesized polymers.

Enhanced hydrogen storage performance of Li and Co functionalized h-GaN nanosheets: DFT study

Based on the density functional theory (DFT) computations, we investigated the hydrogen storage performances of alkali metal (Li) and transition metal (Co) decorated the defective GaN nanosheets. Fundamental aspects including the interaction properties, bonding characteristics, adsorption ability, frontier orbital, HOMO–LUMO energy gaps, natural bond orbital (NBO) analysis, projected densities of states (PDOS) and statistical thermodynamic stability have been demonstrated to analyze the interaction properties of H2 molecules. As a theoretical strategy, non-covalent interactions (NCI) and the atoms in molecules (QTAIM) descriptors were performed to depict weak interactions. The LiN-GaN and CoN-GaN systems and the H2 uptake capacity revealed to be 7.78% and 5.55%, respectively. Our results demonstrated that H2 molecules are introduced sequentially on the Li and Co that functionalized both sides of VN-GaN nanosheets yielded the gravimetric densities up to 8.158% (2Co-VN-GaN) that well above the gravimetric DOE achieve. The 2LiN-GaN and 2CoN-GaN are energetically more effective for the H2 adsorption, stable and preferred than pristine GaN nanosheet.Additionally, two binding mechanisms including polarization of the hydrogen molecules and σ orbitals hybridization of H2 molecules have been investigated to explain the interaction of H2 molecules. The hydrogen desorption enthalpy and desorption temperatures of hydrogen molecules, indicating the H2 molecules are easy to desorb from Li and Co decorated defective GaN nanosheets. These results suggest the possibility of an excellent and promising nanostructural material to improve the performance of hydrogen storage for in fuel cells application at ambient temperature.

H2 Uptake and Diffusion Characteristics in Sulfur-Crosslinked Ethylene Propylene Diene Monomer Polymer Composites with Carbon Black and Silica Fillers after High-Pressure Hydrogen Exposure Reaching 90 MPa

We investigated the influence of two fillers-CB (carbon black) and silica-on the H2 permeation of EPDM polymers crosslinked with sulfur in the pressure ranges 1.2-90 MPa. H2 uptake in the CB-blended EPDM revealed dual sorption (Henry's law and Langmuir model) when exposed to pressure. This phenomenon indicates that H2 uptake is determined by the polymer chain and filler-surface absorption characteristics. Moreover, single sorption characteristics for neat and silica-blended EPDM specimens obey Henry's law, indicating that H2 uptake is dominated by polymer chain absorption. The pressure-dependent diffusivity for the CB-filled EPDM is explained by Knudsen and bulk diffusion, divided at the critical pressure region. The neat and silica-blended EPDM specimens revealed that bulk diffusion behaviors decrease with decreasing pressure. The H2 diffusivities in CB-filled EPDM composites decrease because the impermeable filler increases the tortuosity in the polymer and causes filler-polymer interactions; the linear decrease in diffusivity in silica-blended EPDM was attributed to an increase in the tortuosity. Good correlations of permeability with density and tensile strength were observed. From the investigated relationships, it is possible to select EPDM candidates with the lowest H2-permeation properties as seal materials to prevent gas leakage under high pressure in H2-refueling stations.

Cerium-promoted nickel catalysts supported on yttrium-doped γ-alumina for carbon dioxide methanation

The catalytic performance of the Ni/Al, Y-doped Ni/Al-xY, and Ce-promoted Ni-yCe/Al-15Y catalysts for CO2 methanation was examined. The CO2 conversion and CH4 yield increased in the order of Ni/Al < Ni/Al-5Y < Ni/Al-25Y < Ni/Al-15Y at temperatures below 350 °C. The reduction degree, H2 uptake, and total CO2 adsorption uptake increased in this order for the Ni/Al-xY catalysts, suggesting that doping γ-Al2O3 with a moderate amount of Y improved the interaction between the nickel and the support. When the Ni/Al-15Y catalyst was promoted by Ce with different contents (0–5 wt%), the catalyst with 2 wt% Ce exhibited the highest CO2 conversion (92.5%) and CH4 yield (92.2%) at ≤ 350 °C. As evidenced by catalyst characterization, cerium promoter results in a synergetic Ni–Ce interaction over the combined Al-15Y support, leading to the formation of finely dispersed metal species and numerous active sites for splitting of the stable C–O bond.

Metal doped tetrahedral silsesquioxane cages for hydrogen storage

The hydrogen adsorption properties of Tetrahedral Silsesquioxane Si4O6H4 (TS) cages doped with Be, Li, Sc and Ti atoms are studied in different spin state using density functional theory with M062X functional. Initially-one of the four hydrogen atoms in TS cage was substituted by metal atoms. Doublet and singlet are the lowest energy state for TS-Be and TS-Li respectively with respective H2 uptake capacity of 1.79 and 3.56 wt%. Triplet and quartet are the lowest energy state for TS-Sc and TS-Ti respectively. TS-Sc (singlet) and TS-Ti (doublet) cage interacts with seven and six hydrogen molecules respectively with respective gravimetric H2 capacity of 5.25 and 4.51 wt%. TS-Sc in triplet state could adsorb six H2 molecules whereas TS-Ti in quartet state could adsorb five H2 molecules with respective H2 uptake capacity of 4.5 wt% and 3.7 wt%. Then all the four hydrogen atoms in a TS cage are substituted by four Be, Li or Sc atoms (lowest energy state is Singlet for all the three) with respective hydrogen uptake capacity of 6.19, 12.69 and 12.01 wt%. When all the four hydrogens in TS cage are substituted by four Ti atoms, clustering of Ti atoms occurs and the cage structure gets distorted and therefore not considered for H2 adsorption. H2 adsorption on one Be(doublet), Sc(triplet) and Ti(quartet) atom doped TS cage is thermodynamically favourable below 210, 160 and 320 K respectively at 1 atm. pressure. At room temperature, it is thermodynamically favourable at higher pressure also. Four Sc and Be atom doped TS cages are found to be thermodynamically suitable for hydrogen storage below 210 K at 1 atm pressure. It is also suitable at room temperature but at higher pressure. One as well as four Li atom doped TS cages are not suitable for hydrogen storage for the entire temperature and pressure range considered. Molecular dynamics simulations performed using atom centered density matrix propagation (ADMP) show that the loosely bonded H2 molecules fly away during the simulations.

Hydrogen gas permeation in peroxide‐crosslinked ethylene propylene diene monomer polymer composites with carbon black and silica fillers

AbstractThis study investigated the effect of two types of fillers, carbon black (CB) and silica, on the H2 permeation of peroxide‐crosslinked ethylene propylene diene monomer (EPDM) polymers at different pressures (1.2–9.0 MPa). The H2 uptake was linearly correlated with the exposure pressure in all specimens. The H2 solubility in the filled EPDM composites also increased linearly with an increase in the filler content. The H2 solubility was determined by the absorption of polymer networks and adsorption at the filler surface in the CB‐filled EPDM. Meanwhile, the H2 solubility in neat and silica‐filled EPDM was dominated by the polymer network absorption. In the filled EPDM, H2 diffusivity decreased because the filler increased the tortuosity of the polymer. The effects of filler on H2 permeation were largest in the high‐abrasion and semi‐reinforcing furnaces, while the effects were lowest in the silica filler. This trend was associated with the surface area and interface of the fillers. The correlations of the average diffusivity (or permeability) with the filler content and crosslink density of the composites were observed and discussed. From the resulting relationships, we can predict the H2 permeation properties of the compounded EPDM candidates, when used as seal materials, under high‐pressure environment in H2‐refueling stations.