Lithium decoration of boron-doped hybrid fullerenes and nanotubes as a novel 3D architecture for enhanced hydrogen storage: A DFT study

A three dimensional (3D) dumbbell-like nanostructure composed by interconnected fullerenes and nanotubes with Lithium decoration and boron-doping (37Li@C₁₃₉B₃₁) has been proposed in virtue of density functional theory (DFT) and first-principles molecular dynamics (MD) simulations which shows excellent geometric and thermal stability. First-principles calculations are performed to investigate the hydrogen adsorption onto the 37Li@C₁₃₉B₃₁. The results indicate that B substitution can improve the metal binding and the average binding energy of 37 adsorbed Li atoms on the C₁₃₉B₃₁ (2.79 eV) is higher than the cohesive energy of bulk Li (1.63 eV) suppressing the clustering. Meanwhile, the H₂ storage gravimetric density of 178H₂@37Li@C₁₃₉B₃₁ reaches up to 15.9 wt% higher than the year 2020 target from the US department of energy (DOE). The average adsorption energy of H₂ molecules falls in a desirable range of 0.18–0.27 eV. Moreover, grand canonical ensemble Monte Carlo (GCMC) simulations reveal that at room temperature the hydrogen gravimetric density (HGD) adsorbed on 37Li@C₁₃₉B₃₁ reaches up to 11.6 wt% at 100 bars higher than the DOE 2020 target. Our multiscale simulations indicate that our proposed nanostructure provides a promising medium for hydrogen storage.     

Synthesis and characterization of porous HKUST-1 metal organic frameworks for hydrogen storage

Hydrogen storage capacity has been investigated on a copper-based metal organic framework named HKUST-1 with fine structural analyses. The crystalline structure of HKUST-1 MOF has been confirmed from the powder X-ray diffraction and the average particle diameter has been found about 15–20 μm identified by FE-SEM. Nitrogen adsorption isotherms show that HKUST-1 MOF has approximately type-I isotherm with a BET specific surface area of 1055 m²g⁻¹. Hydrogen adsorption study shows that this material can store 0.47 wt.% of H₂ at 303 K and 35 bar. The existence of Cu (II) in crystalline framework of HKUST-1 MOF has been confirmed by pre-edge XANES spectra. The sharp feature at 8985.8 eV in XANES spectra represents the dipole-allowed electron transition from 1s to 4p_xy. In addition, EXAFS spectra indicate that HKUST-1 MOF structure has the Cu–O bond distance of 1.95 Å with a coordination number of 4.2.     

Li-decorated porous graphene as a high-performance hydrogen storage material: A first-principles study

Development of novel carbon-based nanoporous materials with high reversible capacity and excellent cycling stability is a hot topic in the field of hydrogen delivery and storage. In this work, first-principles calculations are carried out to discuss the hydrogen storage properties of Li-decorated porous graphene (Li-PG). The binding energies, electronic structures, storage capacities of hydrogen on different sites are investigated in details. The computational results show that with the increase of lithium doping concentration, the electron concentration of donor atoms exceeds the N_c value, and as a consequence, the PG changes from the p-type semiconductor to the n-type degenerate semiconductor. The maximum hydrogen adsorption configurations of H1a-H'1b and H2a-H'2b systems are obtained, and the average binding energy of per H₂ molecule is 0.245 eV and 0.263 eV, respectively. Furthermore, ab inito MD simulation results show that the H1-H'1 and H2-H'2 systems can hold up to sixteen and fifteen H₂ molecules, which corresponds to a hydrogen storage capacity of 10.89 wt% and 10.79 wt% at T = 300 K (no external pressure), respectively.     

Boron-doping effect on the enhanced hydrogen storage of titanium-decorated porous graphene: A first-principles study

The exploitation of solid hydrogen storage materials is an important part of the large-scale application of hydrogen energy. However, Metal agglomeration is one of the main reasons that restrict the hydrogen storage performance of carbon-based hydrogen storage materials. Herein, we develop Ti-decorated boron doped porous graphene as a novel hydrogen storage material based on first-principles calculations. The geometry and electronic structure of Ti-decorated porous graphene with and without boron doped are calculated. Doping boron in porous graphene (PG) can significantly increase the metal-substrate interaction and prevents the formation of Ti-metal clusters. The Ti atom-decorated boron-doped porous graphene (Ti–B/PG) system can stably adsorb sixteen hydrogen molecules with a gravimetric hydrogen uptake of 8.58 wt%. The thermodynamic calculations prove a high usable capacity of the material, at the adsorbing and desorbing conditions of 25 °C, 30 atm and 100 °C, 3 atm. The excellent hydrogen capacity, good recyclability, and desirable desorption capacity of Ti–B/PG make it a very prospective material for hydrogen storage.     

Polyacrylonitrile-based highly porous carbon materials for exceptional hydrogen storage

In this paper, a common low-cost chemical material-polyacrylonitrile (PAN) is transformed into porous carbon with excellent specific surface area (2564.6–3048.8 m² g⁻¹) and highly concentrated micropore size distribution (0.7–2.0 nm). Benefit to the unique structure, the as-prepared materials show appealing hydrogen adsorption capacity (4.70–5.94 wt % at 20 bar, 7.15–10.14 wt % at 50 bar), demonstrating a promising prospect of practical application. This work also confirmed that the narrow and deep ultramicropore (<0.7 nm) could facilitate adsorption of hydrogen molecules significantly at atmospheric pressure, and the volume increase of supermicropore (0.7–2.0 nm) could lead to hydrogen capacity promotion at relative high pressure (>20 bar), which provides valuable guidance for the construction of ideal porous adsorbent for efficiency hydrogen storage.     

Theoretical modelling of porous silicon decorated with metal atoms for hydrogen storage

There is experimental evidence suggesting that metal adatoms enhance the physisorption of hydrogen molecules in porous silicon. However, theoretical reports about the physical properties for this material to be suitable for hydrogen storage are scarce. Thus, in this work we employ Density Functional Theory to study the effects of decoration with metals on the hydrogen-adsorption properties on hydrogen-passivated porous silicon. The results indicate that lithium and palladium decorating atoms are strongly bonded to the porous silicon—preventing the adverse effects of clusterization—while beryllium is not. Lithium and palladium exhibit physisorption capacity up to 5 and 4 hydrogen molecules per adatom, respectively. In contrast, adsorption of hydrogen molecules in beryllium is too weak as the adatom is not chemisorbed on the surface of the pore. The hydrogen passivation of the pore surface proves to be beneficial for a strong chemisorption of the decorating atoms.     

Enhanced hydrogen storage performances of LiBH4 modified with three-dimensional porous fluorinated graphene

Novel fluorinated graphene (FG) nano-sheets with three-dimensional (3D) porous structure were synthesized by one-pot hydrothermal reaction, and then ball milled with LiBH₄ to prepare the hydrogen storage composite material. The LiBH₄ with 20 wt.% FG composite begins to release hydrogen at 204 °C, 120 °C lower than that of pure LiBH₄. Moreover, it can release 3.45 wt.% hydrogen at 400 °C within 1000 s, which is 2.57 times faster than pure LiBH₄. The reversibility of the LiBH₄–FG composite also has been enhanced, its absorption capacity still reaches 78.6% of initial hydrogen uptake at the 4th cycle. According to the phase composition analyses, F^– can partially substitute the anionic H in LiBH₄ or LiH, resulting in a favorable thermodynamic modification. Additionally, the activation energy (E_a) of hydrogen desorption of LiBH₄ is reduced from 181.80 kJ/mol to 130.87 kJ/mol. The remarkably improved hydrogen storage performances of LiBH₄ are largely attributed to the combined effects of the nano-modifying and the function of F anion of the FG.     

Graphene pillared with hybrid fullerene and nanotube as a novel 3D framework for hydrogen storage: A DFT and GCMC study

A new-type 3D pillared graphene framework with hybrid fullerene and nanotube pillars (PGF-hFN) has been created depended on density functional theory (DFT) and first-principles molecular dynamics simulations (MD). It is proved to have excellent thermal structural stability. The average adsorption energy of Li is 2.77 eV much higher than the metal cohesive energy excluding lithium aggregation problem. From DFT calculations, for Li-decorated B-doped PGF-hFN, the hydrogen gravimetric density (HGD) is as high as 12.92 wt% and the according volumetric uptake is 96.4 g/L with an average adsorption energy of 0.195 eV per H₂. Further grand canonical Monte Carlo (GCMC) simulations predict 7.2 wt% in excess HGD and 53.8 g/L in excess volumetric hydrogen density at near ambient temperature (233 K) and 100 bars with the ideal adsorption enthalpy which have exceeded the 2020 the U.S. Department of Energy (DOE) ultimate target for mobile applications. Our multiscale theoretical simulations indicate this new pillared structure should be a promising carrier accessible for sorption of hydrogen molecules.     

Melaleuca bark based porous carbons for hydrogen storage

Typical porous carbons were obtained from waster biomass, melaleuca bark activated by potassium hydroxide (KOH), and characterized by XRD, SEM, TEM, FTIR, XPS and N₂-sorption. The different samples with tunable morphologies and texture were prepared by controlling synthesis reaction parameters. The resulting samples demonstrate both high surface area (up to 3170 m² g⁻¹) and large hydrogen storage capacity (4.08 wt% at 77 K and 10 bar), implying their great potential as hydrogen storage materials.     

Lithium hydrazide as a potential compound for hydrogen storage

The Metal–N–H system for hydrogen storage has been developed in recent years and is considered to be a promising solution. Here we report a potential compound for hydrogen storage, LiNHNH₂, which is a white solid with 8.0 mass% theoretical hydrogen content and can be synthesized from anhydrous hydrazine and n-butyllithium in diethyl ether. The thermodynamic behaviours and hydrogen storage properties of this compound were firstly investigated and are discussed in this paper. We demonstrate the decomposition pathway of LiNHNH₂ and reveal that an alkali metal hydride such as LiH can significantly increase the hydrogen desorption from LiNHNH₂. Moreover, LiNHNH₂ can also be used for destabilizing other hydrogen storage systems owing to its instability.     

Significant enhancement of the electrochemical hydrogen uptake of reduced graphene oxide via boron-doping and decoration with Pd nanoparticles

Development of advanced hydrogen storage materials with high capacity and stability is vital to achieve an envisaged hydrogen economy. Here, we report a uniformly dispersed Pd nanoparticles on the boron-doped reduced graphene oxide (Pd/B-rGO) as a novel nanocomposite for efficient hydrogen storage. The effects of the incorporation of Pd NPs and the substitution of boron atoms into the graphene-based nanomaterial matrix on the electrochemical hydrogen up-taking and releasing were comparatively studied using electrochemical techniques, and duly supported by density functional theory (DFT) calculations. The discharge capacities of the Pd-rGO and Pd/B-rGO nanocomposites were determined to be over 45 and 128 times higher than that of the Pd NPs, respectively, showing that the B doping and the rGO support played significant roles in the enhancement of the hydrogen storage capability. Moreover, the galvanostatic charging and discharging cycling tests demonstrated a high stability and efficient kinetics of the Pd/B-rGO nanocomposite in the H₂SO₄ electrolyte for hydrogen up-taking and release.     

Exfoliated MoS2 with porous graphene nanosheets for enhanced electrochemical hydrogen evolution

Porous graphene (P-rGO) was synthesized from graphene oxide (GO) via a one-pot calcination method with CO₂ as an activation agent at 800 °C. Due to the special porous structure, the surface area of P-rGO can be increased to ～759 m²/g. The P-rGO was then used as a support to incorporate with chemical exfoliated molybdenum disulfide (MoS₂) for the fabrication of MoS₂/P-rGO composite. Compared to bulk MoS₂, the exfoliated MoS₂ is in the 1T phase with a metallic property and smaller charge transfer resistance, thus has a better activity in electrochemical hydrogen evolution reaction (HER). The HER activity of 1T MoS₂ could be further increased after the combination with P-rGO. The overpotential of 1T MoS₂/P-rGO was only ～130 mV vs. RHE, and the corresponding Tafel slope was ～75 mV Dec^?1. The special porous structure and good electric conductivity of P-rGO decrease the charge transfer resistance of the composite without sheltering too many active sites of MoS₂, thus leading to the enhanced HER activity. As an efficient noble metal free HER catalyst, the 1T MoS₂/P-rGO has great potential for large-scale hydrogen production.     

Stabilized Li-decoration and enhanced hydrogen storage on reduced graphene oxides

Hydrogen storage properties of Li-decorated graphene oxides containing epoxy and hydroxyl groups are studied by using density functional theory. The Li atoms form Li₄O/Li₃OH clusters and are anchored strongly on the graphene surface with binding energies of −3.20 and −2.84 eV. The clusters transfer electrons to the graphene substrate, and the Li atoms exist as Li⁺ cations with strong adsorption ability for H₂ molecules. Each Li atom can adsorb at least 2H₂ molecules with adsorption energies greater than −0.20 eV/H₂. The hydrogen storage properties of Li-decorated graphene at different oxidation degrees are studied. The computations show that the adsorption energy of H₂ is −0.22 eV/H₂ and the hydrogen storage capacity is 6.04 wt% at the oxidation ratio O/C = 1/16. When the O/C ratio is 1:8, the storage capacity reaches 10.26 wt% and the adsorption energy is −0.15 eV/H₂. These results suggest that reversible hydrogen storage with high recycling capacities at ambient temperature can be realized through light-metal decoration on reduced graphene oxides.     

Novel porous carbons synthesized from polymeric precursors for hydrogen storage

In this work, porous carbons were prepared from polymeric ion-exchangeable resin by a chemical activation method in order to obtain novel hydrogen storage materials, and the adsorption characteristics of the porous carbons were investigated. The textural properties were studied by BET and D–R methods with adsorption isotherms. The hydrogen storage behaviors of the porous carbons at 298 K and 100 bar were studied using a PCT apparatus. In the observed post-activation result, the hydrogen storage capacity was markedly improved. However, it was also found that the total amount of adsorption was not proportional to the specific surface area of the adsorbates. This indicates that hydrogen storage could be a function not only of specific surface area or total pore volume but also of microporevolume fraction or the average pore size of adsorbents.     

Macroscale evaluation and testing of chemically hydrogenated graphene for hydrogen storage applications

The effective storage of H₂ gas represents one of the major challenges in the wide spread adoption of hydrogen powered fuel cells for light vehicle transportation. Here, we investigate the merits of chemically hydrogenated graphene (graphane) as a means to store high-density hydrogen fuel for on demand delivery. In order to evaluate hydrogen storage at the macroscale, 75 g of hydrogenated graphene was synthesized using a scaled up Birch reduction, representing the largest reported synthesis of this material to date. Covalent hydrogenation of the material was characterized via Raman spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). We go on to demonstrate the controlled release of H₂ gas from the bulk material using a sealed pressure reactor heated to 600 °C, identifying a bulk hydrogen storage capacity of 3.2 wt%. Additionally, we demonstrate for the first time, the successful operation of a hydrogen fuel cell using chemically hydrogenated graphene as a power source. This work demonstrates the utility of chemically hydrogenated graphene as a high-density hydrogen storage medium, and will be useful in the design of prototype hydrogen storage systems moving forward.     

Addition of transition metals to lithium intercalated fullerides enhances hydrogen storage properties

We report an innovative synthetic strategy based on the solid state reaction of fullerene C₆₀ with lithium-transition metals alloys (platinum and palladium), which provides transition metal-decorated lithium intercalated fullerides, with improved hydrogen storage properties. Compounds with Li₆Pt_0.11C₆₀ and Li₆Pd_0.07C₆₀ stoichiometry were obtained and investigated with manometric/calorimetric techniques which showed an 18% increase of the final H₂ absorbed amount with respect to pure Li₆C₆₀ (5.9 wt% H₂) and an improved absorption process kinetic. The absorption mechanism was investigated with X-rays diffraction which allowed to identify the formation of the hydrofullerides. Scanning Electron Microscopy was applied to gain information on transition metal distribution and detected the presence of platinum and palladium aggregates which are shown to perform a surface catalytic activity towards hydrogen molecule dissociation process.     

Novel metal graphene framework (MGF) structures for hydrogen storage

Hierarchical novel metal graphene framework (MGF) structures designed, constructed and used for hydrogen storage by adsorption. Three different amounts of pillars used for connecting carboxylate functionalized graphene layers. The three-dimensional atomistic models optimized and then the aqua molecules removed which are coordinated to metal between graphene layers as bridge. Hydrogen storage abilities of aqua free models also investigated. The aqua existence made the structures more effective to store hydrogen according to simulation results. The highest storage capacity calculated for 181C.Aq named structure that includes aqua molecules inside could store 7.745 wt percentage hydrogen at 77 K and 100 bars pressure conditions. Hydrogen storage capacity decreases almost to half by removing aqua molecules for same structure. It is clear the coordinated aqua existence around the bridging atoms provides the spaces between graphene layers. In other word, the spaces between the graphene layers collapse by aqua removal so the hydrogen storage capacities decrease dramatically. Finally, spacing between graphene layers by bridges makes them very effective for hydrogen storage.     

Improved design of metal-organic frameworks for efficient hydrogen storage at ambient temperature: A multiscale theoretical investigation

A multiscale theoretical technique is used to examine the combination of different approaches for hydrogen storage enhancement in metal-organic frameworks at room temperature and high pressure by implementation lithium atoms in linkers. Accurate MP2 calculations are performed to obtain the hydrogen binding sites and parameters for the following grand canonical Monte Carlo (GCMC) simulations. GCMC calculations are employed to obtain the hydrogen uptake at different thermodynamic conditions. The results obtained demonstrate that the combination of different approaches can improve the hydrogen uptake significantly. The hydrogen content reaches 6.6 wt% at 300 K and 100 bar satisfying DOE storage targets (5.5 wt%).     

Catenated metal-organic frameworks: Promising hydrogen purification materials and high hydrogen storage medium with further lithium doping

Based on the first-principles derived force fields and grand canonical Monte Carlo simulations, we find that the catenated metal-organic frameworks outperform the noncatenated structures, in terms of H₂ separation from other gases (CH₄, CO and CO₂) and H₂ adsorption by Li doping. A system utilizing IRMOF-11 (or IRMOF-13) for hydrogen separation and Li-doped IRMOF-9 for hydrogen storage is therefore proposed, with hydrogen uptake of 4.91 wt% and 36.6 g/L at 243 K and 100 bar for Li-doped IRMOF-9, which is close to the 2017 DOE target. It is promising to find appropriate microporous materials for hydrogen purification and storage at ambient conditions with structure catenated.     

SANS characterization of porous magnesium for hydrogen storage

Porous magnesium was produced through the thermal decomposition of various additives in an effort to increase hydrogen storage capacity. Samples were characterized using SANS and different theoretical models were applied to the results and discussed. The polydisperse self-assembled (PSA) model was found to best represent the scattering from these materials as this model incorporates the polydispersity of the pores and allows for variations in structure factor. Pure magnesium produced using the same thermal method absorbed a negligible amount of hydrogen, and hydrogen uptake was found to increase with increasing porosity as determined using the PSA model. Maximum hydrogen uptake (1.3%) was found when 0.3% Cs₂CO₃ and 0.5% Ni were combined as an additive during thermal treatment. In addition, the development of porosity was found to promote hydrogen desorption at lower temperatures. SANS represents an indispensible method by which to characterize materials and the PSA model described in this work has the potential to be extremely useful in the characterisation of porous metallic systems.