Gravimetric H2 Research Articles

Theoretical prediction of perovskite ARH3 (A = K, Li, Rb; R[dbnd]Ca, Sr) hydride materials for hydrogen storage applications: A DFT investigation

Hydrogen (H2) storage has attracted the greatest attention in the contemporary day because of the shortage of fuel. The water splitting is considered less cost-effective and lead-free energy production by the photocatalytic process to produce hydrogen as a fuel for vehicles, petroleum refining, Pharmaceuticals, and glass purification. Perovskite materials play a vital role in H2 storage and production applications. The density functional theory (DFT) using the CASTEP code is used to study the various structural, electrical, optical, mechanical, and hydrogen (H2) capacity properties of ARH3 (A = K, Li, Rb; RSr, Ca) compounds. The compounds under investigations are optimized in the cubic structure; for ARH3 (A = K, Li, Rb; RSr, Ca), the optimized lattice constants are 3.924, 4.302, 4.559, 4.817, 4.647, and 4.884 Å, respectively. Since these hydrides are thermally stable, their formation energy is exhibited negative values. ARH3 may find usage in H2 storage applications due to its high gravimetric H2 storage densities (6.042 and 3.678 wt% for LiCaH3 and KCaH3, respectively). Furthermore, band gaps of 2.71, 2.38, 3.27, 2.73, 1.85, and 2.83 eV for ARH3 (A = K, Li, Rb; RCa, Sr) respectively, confirm the semiconductor behavior. These substances satisfy born stability criteria due to its mechanical parameters which derived from elastic constant values such as Pugh's ratio and modulus. Additionally, Pugh's ratio and Cauchy pressure demonstrate that, in contrast to other compounds, the KCaH3 compound has a ductile character (0.29). According to our analyses, studied compounds are observed a potential candidate for hydrogen storage devices.

Establishing ZIF-8 as a reference material for hydrogen cryoadsorption: An interlaboratory study.

Hydrogen storage by cryoadsorption on porous materials has the advantages of low material cost, safety, fast kinetics, and high cyclic stability. The further development of this technology requires reliable data on the H2 uptake of the adsorbents, however, even for activated carbons the values between different laboratories show sometimes large discrepancies. So far no reference material for hydrogen cryoadsorption is available. The metal-organic framework ZIF-8 is an ideal material possessing high thermal, chemical, and mechanical stability that reduces degradation during handling and activation. Here, we distributed ZIF-8 pellets synthesized by extrusion to 9 laboratories equipped with 15 different experimental setups including gravimetric and volumetric analyzers. The gravimetric H2 uptake of the pellets was measured at 77 K and up to 100 bar showing a high reproducibility between the different laboratories, with a small relative standard deviation of 3-4 % between pressures of 10-100 bar. The effect of operating variables like the amount of sample or analysis temperature was evaluated, remarking the calibration of devices and other correction procedures as the most significant deviation sources. Overall, the reproducible hydrogen cryoadsorption measurements indicate the robustness of the ZIF-8 pellets, which we want to propose as a reference material.

Vanadium-decorated 2D polyaramid material for high-capacity hydrogen storage: Insights from DFT simulations

Herein, systematic computational investigations comprising density functional theory and ab initio molecular dynamics simulations (AIMD) have been conducted to assess the viability of vanadium decoration over the newly synthesized 2D polyaramid material (2DPA-I) as a potentially reversible hydrogen storage substrate for light fuel cell vehicles. The binding energies of V at different positions over 2DPA-I were compared, and the optimum site for V decoration was in the plane of 2DPA-I. The H2 binding ability of V-decorated 2DPA-I was improved over that of pristine 2DPA-I by 185.71 %. A single V atom decorated over 2DPA-I can effectively bind 7 H2 molecules, with a gravimetric H2 storage capacity of ~7.3 wt% and desorption temperature ~330 K at a favourable binding energy window (~−0.4 eV) to facilitate reversible H2 binding. V-decorated 2DPA-I remained stable at elevated temperatures as verified by AIMD simulations, and a substantial energy barrier of ~3 eV exists for the movement of the V atom across the 2DPA-I surface. The interaction of V with 2DPA-I and H2 with V-decorated 2DPA-I proceeds with a charge flow from the V atom towards H2 and 2DPA-I, respectively. The binding energy and charge transfer analysis of the interaction of H2 with V-decorated 2DPA-I indicates possible Kubas interactions. We predict that V-decorated 2DPA-I has immense potential for on-board H2 storage applications in light fuel cell vehicles.

Application of green energy and environment-friendly decorative composite materials by using kinetic model with Sodium Alanate Nano carbon particle for building technologies

Hydrogen energy is the main key point to make the long-term energy be secure. The unit of an economic system is completed by hydrogen generation, storage, transit, and use. Nonetheless, its storage strategies have clashed with applications that need hydrogen on board. The zero-energy idea was designed to assist in the development of energy policies with the goal of developing and constructing sustainable communities and structures. The higher the scale, the more plausible a zero-energy hydrogen economy is. H2 and fuel cell storage work together optimally to reduce uncertainty. The potential systems based on Sodium Alanate (SA) under the kinetic model was motivated by the extensive use and intriguing features of diverse silicon carbon nanomaterials. The electrical characteristics, structural stability, and adsorption energies of hydrogen molecules are investigated. Sodium Alanate is used in hydrogen gas release to investigate its feasibility. Hydrogen sorption procedure inside a storage container is modeled based on hydrogen transport equations, generated heat transfers and kinetic formulas. In this research, a numerical solution is created and verified using previously acquired empirical findings. This study defines and optimizes the gravimetric H2 storage potential on the basis of SA using numerical simulation data.

Metallized HOT-graphene: A novel reversible hydrogen storage medium with ultrahigh capacity

By performing first-principles calculations, we have researched the hydrogen storage capability of the alkali metals (Li, Na, K) and alkali-earth metal (Ca) decorated HOT graphene, a novel excellent Dirac semimetal which consists of hexagon, octagon and tetragon carbon rings. Metal Li, Na, K and Ca can be strongly bonded on HOT graphene with very large binding energy instead of forming clusters. Each metal can absorb maximum of 3, 5, 5 and 6 H2, respectively, and the average adsorption energy are all in the reversible hydrogen storage range. In the case of double-sided adsorption, 16 metals can be loaded on 2 × 2 × 1 supercell of HOT graphene and then come into being gravimetric H2 uptake of 12.34 wt%, 14.59 wt%, 11.83 wt% and 13.71 wt% for Li, Na, K and Ca decorated HOT graphene, separately, which significantly exceeds the DoE standard (6.5 wt%). The analysis of the calculated electronic density of states and charge transfer indicates that the strong bonding between metal atoms and HOT graphene is derived from orbital interaction concerning charge transfer, while the adsorption of hydrogen molecule attributes to the polarization of hydrogen molecule near ionized metal atoms and thus electrostatic and van der Waals interactions render H2 to adsorb in the metal atoms. Finally, the integrity of metal decorated HOT graphene based on ab-initio molecular dynamics (AIMD) calculation at corresponding H2 desorption temperatures indicates that the feasibility of practical application of metallized HOT-graphene system as reversible hydrogen storage medium with ultrahigh capacity. And these findings could be expected to facilitate experimental studies.

Heteroborospherene decorated with light metal as high capacity hydrogen storage material: Theoretical perspectives

In this work, the hydrogen storage capability in light metal (Na and K) decorated heteroborospherene C4B32 was investigated by using density functional theory (DFT) calculations. Na atoms can strongly bind to C4B32 with the average binding energy of 2.720 eV. The clusters of Na atoms decorated C4B32 are observed to be structurally stable even after the adsorption of H2 molecules. Each Na atom can adsorb 6H2 molecules with average adsorption energy of 0.199 eV/H2 yielding gravimetric H2 uptake of 8.99 wt%. However, the average adsorption energy of H2 molecules in K4C4B32 is much less than 0.2 eV. Therefore, Na decorated heteroborospherene C4B32 can act as an effective material for reversible H2 storage.

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.

Tuning the isomer composition is a key to overcome the performance limits of commercial benzyltoluene as liquid organic hydrogen carrier

This work is the outcome of a three-year journey to develop a technically feasible way to overcome the limits of the benzyltoluene (H0-BT) and perhydro benzyltoluene (H12-BT) pair, recognized as an attractive liquid organic hydrogen carrier (LOHC) system. In the first attempt to synthesize and evaluate three H0-BT regioisomers, the para isomer showed faster H2 storage and release rates than the ortho and meta counterparts. This was attributed to its favorable adsorption capacity and strength on the catalyst surface. The subsequent evaluation of binary and ternary H0-/H12-BT isomeric mixtures, prepared by physical mixing the synthesized isomers, suggested that abundant amounts of para isomer in the mixture were needs to maximize the LOHC performance. Thus, a H0-BT mixture with 72 % para isomer was successfully synthesized using the zeolite H-Beta under optimized conditions, resulting in a faster kinetics of both H2 storage and release than commercial Marlotherm LH. Cycling tests on this mixture indicated that the formation of methylfluorene as a dehydrogenation byproduct was detrimental to the hydrogenation reaction. By reducing the formation of methylfluorene to a level of 3 % using a sulfur-decorated Pt/Al2O3 catalyst, a gravimetric H2 storage density of 6 wt% could be maintained for 10 cycles. Finally, a cost analysis confirmed that the isomeric composition of H0-BT in the mixture should be tuned to increase the para isomer content, while the raw materials for H0-BT synthesis are cheap. The step-by-step approach reported herein will pave the way for the development of novel aromatic LOHC systems in the near future.

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.

Heterofullerene C48B12-impregnated MOF-5 and IRMOF-10 for hydrogen storage: A combined DFT and GCMC simulations study

The H2 storage properties of isoreticular metal-organic framework materials (IRMOFs), MOF-5 and IRMOF-10, impregnated with different numbers and types of heterogeneous C48B12 molecules were investigated using density functional theory and grand canonical Monte Carlo (GCMC) calculations. The excess hydrogen adsorption isotherms of IRMOFs at 77 K within 20 bar indicate that suitable number and type of C48B12 molecules play a crucial role in improving the H2 storage properties of IRMOFs. Among the studied pure and nC48B12 (n = 1, 2, 4, 8) in Ci symmetry impregnating into MOF-5, at 77 K under 6 bar, MOF-5-4C48B12 with a 3.5 wt% and 29.9 g/L hydrogen storage density, and at 77 K under 12 bar, the pure MOF-5 with a 4.9 wt% and 31.0 g/L hydrogen storage density has the best hydrogen storage properties. Whereas, among the studied pure and nC48B12 (n = 1, 2, 4, 8) in S6 symmetry impregnating into IRMOF-10, IRMOF-10-8C48B12 always shows the best hydrogen storage properties among the pure and C48B12-impregnated IRMOF-10 at 77 K within 20 bar. IRMOF-10-8C48B12 has a 6.0 wt% and 34.6 g/L hydrogen storage density at 77 K under 6 bar, and has a 7.1 wt% and 41.4 g/L hydrogen storage density at 77 K under 12 bar. The confinement effect of IRMOFs on C48B12 molecules, and steric hindrance effect of C48B12 molecules on IRMOFs mainly affects the H2 uptake capacity by comparing the absolute H2 molecules in individual IRMOFs units, C48B12 molecules, and IRMOFs-nC48B12 compounds. The absolute hydrogen adsorption profiles show that eight C48B12 molecules impregnating into MOF-5 can exert obvious steric effects for H2 adsorption. The saturated gravimetric and volumetric H2 densities of IRMOF-10-8C48B12 higher than those of MOF-5-8C48B12 due to with larger free volume.

Where to go for the Development of High-Performance H2 Storage Materials at Ambient Conditions?

Hydrogen is expected to overcome energy resource depletion because it is the most abundant element in the universe and because an ideal hydrogen energy cycle has the potential to exploit energy infinitely. Conventionally, hydrogen storage utilizes compression under high pressure (350–700 bar) into a tank and liquefaction in the cryotemperature regime (20 K). To mitigate the impractical operating conditions researchers have conducted adsorption-dependent research to increase the specific surface area (SSA) in physisorption and to decrease the H2 binding energy in chemisorption. Nevertheless, these strategies are still unlikely to reach the required the U.S. Department of Energy (DOE) targets. To this end, researchers have tried to find hydrogen storage material to fit the H2 binding energy between the physisorption region and chemisorption region. Previous governing parameters, the SSA, and the H2 binding energy show no correlation to gravimetric H2 storage capacity (GHSC). In addition, no correlation between the H2 densification index (HDI) and the H2 binding energy is found as well, which means the latter cannot describe the H2-adsorbent interaction thoroughly. The several notable findings presented here suggest that the development of high-performance H2 storage materials can be realized through the optimal modulation of an underlying parameter that dominates the H2-adsorbent interaction. This paper highlights the necessity of research on what the underlying parameter that dominates the H2-adsorbent interaction is and on how it affects GHSC to develop H2 storage materials that meet the DOE targets.Graphical abstract

Ammonia as a hydrogen energy carrier

The gravimetric H2 densities and the heats of combustion of tanks stored ammonia (ammonia storage tanks) were similar to those of the liquid H2 tanks at the weight of 20–30ton, although the gravimetric H2 density of liquid H2 is 100 wt%. The volumetric H2 densities and the heats of combustion of ammonia storage tanks were about 2 times higher than those of liquid H2 tanks at 1–4 × 104 m3. Gray ammonia is synthesized from hydrogen through process known as steam methane reforming, nitrogen separated from air and Haber-Bosch process. Blue ammonia is the same as gray ammonia, but with CO2 emissions captured and stored. Green ammonia is produced by reacting hydrogen produced by electrolysis of water and nitrogen separated from air with Haber-Bosch process using renewable energies. The energy efficiencies of gray, blue and green ammonia were better than those of liquid hydrogen and methylcyclohexane (MCH) with high H2 density and similar to the efficiency of H2 gas. The energy efficiencies of ammonia decreased in the order, gray ammonia > blue ammonia > green ammonia. The production costs of green hydrogen energy carried increased in the order, ammonia < liquid H2<MCH. The amounts of energy consumption by N2 production and Haber-Bosch process were below 10% compared with the value of H2 production from water electrolysis.

Catalytic effect of Al2TiO5 on the dehydrogenation properties of LiAlH4

Lithium alanate (LiAlH4) is considered as a promising material for storing hydrogen (H2) in solid-state form for onboard applications due to its advantage of high gravimetric H2 capacity. LiAlH4 could release H2 ∼7.9 wt.% when heated up to ∼250 °C. Nevertheless, the high desorption temperature, sluggish desorption kinetics, and irreversibility hamper the application of LiAlH4 for solid-state H2 storage materials. Therefore, in this study, we have used aluminum titanate (Al2TiO5) as an additive to diminish the desorption temperature and enhance the desorption kinetics of LiAlH4. The addition of a small amount of Al2TiO5 (5 wt.%) into LiAlH4 significantly decreased the decomposition temperature and enhanced the desorption kinetics, in which Al2TiO5-doped LiAlH4 started to release H2 at ∼90 °C and was able to desorb H2 as much as ∼3.5 wt.% at 90 °C within 1 h. Without the catalyst, pure LiAlH4 starts to release H2 at ∼145 °C and only desorbs H2 as low as 0.3 wt.% at 90 °C within 1 h. The activation energies for H2 release in the two-step desorption process of LiAlH4 were reduced after catalysis with Al2TiO5. The activation energies of as-milled LiAlH4 were 80 kJ/mol and 91 kJ/mol, respectively, as calculated by the Arrhenius plot. The activation energies were lowered to 68 kJ/mol and 79 kJ/mol after milling with Al2TiO5. The scanning electron microscopy images revealed that the LiAlH4 particles became smaller and less agglomerated when Al2TiO5 was added. It is believed that the in-situ formation of active species during the desorption process and reduction in particles size play a vital role in improving the dehydrogenation properties of the Al2TiO5-doped LiAlH4 system.

Fullerene-impregnated IRMOFs for balanced gravimetric and volumetric H2 densities: A combined DFT and GCMC simulations study

This paper aimed to study the effects of fullerene (C60) impregnation on the isoreticular metal-organic framework (IRMOF) materials MOF-650 (ZnO4 nodes were connected to azulenedicarboxylate linkers), MOF-5(ZnO4 nodes were connected to benzenedicarboxylate linkers), and IRMOF-10 (ZnO4 nodes were connected to biphenyldicarboxylate linkers) for H2 storage, these IRMOFs had similar structures but different pore volumes and organic linkers. Density functional theory (DFT) and grand canonical monte Carlo (GCMC) calculations indicated that C60 plays an important role in balancing the gravimetric and volumetric H2 densities of the IRMOFs. The C60@IRMOFs revealed improved volumetric density when H2 was undersaturated but reduced gravimetric density under H2 saturation. The saturated gravimetric H2 density of the IRMOFs was decided by the free volume. At 77 K, C60@MOF-650 had a gravimetric H2 density of 5.3 wt% and volumetric H2 density of 42 g/L under 10 bar, and C60@IRMOF-10 had a gravimetric H2 density of 7.4 wt% and volumetric H2 density of 43 g/L under 18 bar. These values nearly meet the United States Department of Energy (DOE) gravimetric and volumetric H2 density ultimate targets (gravimetric H2 density, 6.5 wt%; volumetric H2 density, 50 g/L) under ambient pressures. Among the studied IRMOFs, C60@MOF-650 and C60@IRMOF-10 demonstrated the best H2 storage properties at 233 and 298 K.

(Invited) Atomic Layer Deposition for H2 Storage: Opportunities and Limitations

The transportation demands in our growing hydrogen (H2) economy requires robust storage systems. The current commercially implemented technology in fuel cell cars relies on the well-established technology of hydrogen gas compressed to 350–700 bar, depending on the application. The compressed gas tanks in use today are bulky and cost intensive. To address this challenge, material-based storage is one of the long-term alternatives considered and constitutes the focus of this talk.Material-based storage is broadly defined as hydrogen bound to solid materials, with its binding strength varying from physisorption to porous materials, such as zeolites and metal organic frameworks, to chemisorption in (complex) metal hydrides. The ultimate targets set by the U.S. Department of Energy for this technology include a system gravimetric capacity of 6.5 wt% and volumetric capacity of 40 g/L at 100 bar, operating temperatures ranging between -40 C and +40 C and adsorption/desorption timescales of < 5 min. Storage in the form of physisorbed or chemisorbed hydrogen has guided the materials research, which metal-organic framework and (complex) metal hydrides being the most promising materials classes. A variety of these materials have met one or more of the targets, but it has remained elusive for a single material system to meet all these stringent requirements. Nano-encapsulation and low-concentration chemical additives have previously been employed separately to overcome such challenges. Functionalization via atomic layer deposition (ALD), however, offers unique characteristics that make it suitable for both, nano-encapsulation and “doping” with low-concentration additives. This deposition technique has sub-monolayer thickness control, is highly conformal in high-surface area materials and is self-limiting, i.e., once the gas-phase precursor reacts with the available surface sites, the surface reactions stop.In this presentation, we will showcase examples where ALD, more generally vapor-phase functionalization, on (complex) metal hydrides and organic frameworks has improved the material properties for H2 storage. In our first study, Al2O3 was deposited on magnesium borohydride, Mg(BH4)2, at room temperature using trimethylaluminum (TMA) and water. From our findings, encouraging initial results were obtained: the H2 desorption temperature was lowered by 60–120 ˚C, the desorbed gravimetric H2 capacity at temperatures < 250 ˚C was doubled, and the desorption kinetics increased by a factor of ~6 compared to uncoated Mg(BH4)2. However, hydrolysis reactions caused by residual surface -OH groups from the ALD water-pulse degraded the sample substantially. Through this study, the use of TMA was observed to be highly reactive with the Mg(BH4)2 surface species, leading to the strategy of exposing the sample only to TMA. The relative mole fraction of the vapor-phase additive can be precisely controlled with the number of TMA pulses and pulse duration. By tuning these parameters, we show in our second study that 10 pulses of TMA at ambient conditions were able to decrease the H2 desorption temperature by ~100 ˚C while retaining <95 % of its H2 capacity. We applied this approach with other additives such as BBr3, TiCl4 and tetrahydrofuran, and demonstrate that this unique approach opens the door to a new class of molecular additives and catalysts which cannot easily be introduced with conventional mechano-chemical or solvent-based techniques for (complex) metal-hydrides. In the case of metal organic frameworks, ALD is a promising technique to functionalize the pores with metal atoms or functional groups able to tune the gas selectivity and binding energy, for which ~15 kJ/mol has been established as the optimal value for H2 storage in sorbent materials.Vapor-phase techniques such as ALD have numerous benefits over other functionalization tools for H2 storage materials opening innumerable opportunities to the field. To exploit these opportunities, the current limitations on room temperature and water-less ALD processes needs to be overcome which will greatly expand the possibilities of encapsulation and incorporation of additives for organic frameworks and (complex) metal hydrides.

Computational screening of zeolite templated carbons for hydrogen storage

Grand Canonical Monte Carlo (GCMC) simulations were used to evaluate the hydrogen storage performance of the 68 stable ZTCs which were recently identified. The relationship between the hydrogen storage capacities and densities, accessible pore volume, specific surface area, and helium void fraction of the 68 ZTC structures at 77 K and 298 K up to100 bar pressure has been investigated. The simulation results revealed that RHO has the highest gravimetric H2 uptake (9.23 wt%) under 77 K and 100 bar condition. The RHO structure also showed better deliverable capacity than other ZTCs under room temperature (1.25 wt%) and cryogenic conditions (8.83 wt%). These results show the high potential of the ZTCs for the future ultra-lightweight hydrogen storage media. The relationship between excess hydrogen capacity and specific surface area was investigated, and it was found that 10.3 mmol/g excess hydrogen capacity per 1000 m2/g specific surface area at 77 K. It was determined that the most effective parameters on the maximum excess hydrogen capacity at 77 K were accessible pore volume and specific surface area. A multiple linear regression model was also proposed to predict maximum excess hydrogen capacity at 77 K.

Nanoporous polymer-derived activated carbon for hydrogen adsorption and electrochemical energy storage

The development and in-depth characterization of multifunctional materials with versatile use in energy and environmental applications has been a topic of on-going investigations. In this work, a nanoporous polymer-/polyaniline-derived activated carbon (PDAC), with large surface area (~2200 m2/g) and large pore volume (~1 cm3/g), was thoroughly studied towards its applicability for H2 storage and supercapacitor energy storage. The PDAC demonstrated a superior H2 adsorption performance under cryogenic conditions, reaching a high and fully reversible excess gravimetric H2 uptake of ~5.5 wt% at 77 K and ~60 bar, along with a ~8.3 kJ/mol heat of adsorption at zero coverage. Furthermore, thin PDAC electrodes with an aqueous CsCl electrolyte were combined in a supercapacitor cell that exhibited a gravimetric capacitance of ~130 F/g for a 0.5 mV/s scanning rate along with a 99% coulombic efficiency and a 100% capacitance retention after 2500 charge/discharge cycles. The PDAC material showed substantially improved H2 and electrochemical energy storage performance compared to a well-established commercial activated carbon, which is attributed to the overall smaller pore sizes of the PDAC structure.

Recent advancement in consolidation of MOFs as absorbents for hydrogen storage

Metal-organic frameworks (MOF) have emerged as a promising material for green engineering applications due to their attractive properties. But the successful implementation of this material in the field of fuel cell technologies is still a challenge. Researchers have reported more than 50% reduction in experimental bulk density of compacted MOFs relatively to their theoretical crystal density. This has resulted in reduction of gravimetric and volumetric H2 storage capacities of MOFs. Significant experimental research should be directed toward the consolidation of MOFs to meet (6.5 wt%; 50 g/L) 2025 DoE target for onboard H2 storage systems. We present an overview of green engineering materials for hydrogen storage systems. The review also summarizes recent advancement in the consolidation of MOFs as absorbents for hydrogen storage. The influence of densification techniques on MOFs textural properties, mechanical stability were discussed. Hydrogen storage capacity of both powder and densified high-performance MOFs were presented.

Synopsis of Factors Affecting Hydrogen Storage in Biomass-Derived Activated Carbons

Hydrogen (H2) is largely regarded as a potential cost-efficient clean fuel primarily due to its beneficial properties, such as its high energy content and sustainability. With the rising demand for H2 in the past decades and its favorable characteristics as an energy carrier, the escalating USA consumption of pure H2 can be projected to reach 63 million tons by 2050. Despite the tremendous potential of H2 generation and its widespread application, transportation and storage of H2 have remained the major challenges of a sustainable H2 economy. Various efforts have been undertaken by storing H2 in activated carbons, metal organic frameworks (MOFs), covalent organic frameworks (COFs), etc. Recently, the literature has been stressing the need to develop biomass-based activated carbons as an effective H2 storage material, as these are inexpensive adsorbents with tunable chemical, mechanical, and morphological properties. This article reviews the current research trends and perspectives on the role of various properties of biomass-based activated carbons on its H2 uptake capacity. The critical aspects of the governing factors of H2 storage, namely, the surface morphology (specific surface area, pore volume, and pore size distribution), surface functionality (heteroatom and functional groups), physical condition of H2 storage (temperature and pressure), and thermodynamic properties (heat of adsorption and desorption), are discussed. A comprehensive survey of the literature showed that an “ideal” biomass-based activated carbon sorbent with a micropore size typically below 10 Å, micropore volume greater than 1.5 cm3/g, and high surface area of 4000 m2/g or more may help in substantial gravimetric H2 uptake of &gt;10 wt% at cryogenic conditions (−196 °C), as smaller pores benefit by stronger physisorption due to the high heat of adsorption.

H2 storage and equilibrium isotope effect for Be, Li, and Ti-doped closoborate complexes

This work reports hydrogen uptake capacity and equilibrium isotope effect (EIE) for the Be, Li, and Ti-doped closoborate (B6H6) complexes using first-principles calculations at MP2/6-311++G** level. The EIE was obtained using vibrational frequencies of H2 and D2-adsorbed B6H6M (M = Be, Li, and Ti) complexes at MP2/6-311++G** level. Two, three, and four H2/D2 molecules get adsorbed on B6H6Be, B6H6Li, and B6H6Ti respectively. The gravimetric H2(D2) uptake capacity of B6H6Be, B6H6Li, and B6H6Ti complexes is found to be 4.8(9.5), 7.2(13.44), and 6.3(11.94) wt% respectively. H2 adsorption is thermodynamically favorable on B6H6Ti at ambient conditions, whereas it is unfavorable on B6H6Li and B6H6Be complexes. Contribution from each vibrational mode in calculating the equilibrium isotope effect is obtained. The EIE calculated using vibrational frequencies for the B6H6Be(1H2/1D2), B6H6Be(2H2/2D2), B6H6Li(1H2/1D2), B6H6Li(2H2/2D2), B6H6Li(3H2/3D2), B6H6Ti(2H2/2D2), B6H6Ti(3H2/3D2), and B6H6Ti(4H2/4D2) complexes is found to be 0.56, 0.26, 0.76, 0.93, 1.05, 0.25, 0.05, and 0.75 respectively. In case of B6H6Ti(1H2) complex, the hydrogen is adsorbed in atomic form. It is found that D2 binds better than the H2 to the B6H6M (M = Be, Li, and Ti) complex.